This is libc.info, produced by makeinfo version 7.1.1 from libc.texinfo. This is ‘The GNU C Library Reference Manual’, for version 2.41 (Buildroot). Copyright © 1993-2025 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "Free Software Needs Free Documentation" and "GNU Lesser General Public License", the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom." INFO-DIR-SECTION Software libraries START-INFO-DIR-ENTRY * Libc: (libc). C library. END-INFO-DIR-ENTRY INFO-DIR-SECTION GNU C library functions and macros START-INFO-DIR-ENTRY * ALTWERASE: (libc)Local Modes. * ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions. * ARG_MAX: (libc)General Limits. * BC_BASE_MAX: (libc)Utility Limits. * BC_DIM_MAX: (libc)Utility Limits. * BC_SCALE_MAX: (libc)Utility Limits. * BC_STRING_MAX: (libc)Utility Limits. * BRKINT: (libc)Input Modes. * BUFSIZ: (libc)Controlling Buffering. * CCTS_OFLOW: (libc)Control Modes. * CHAR_BIT: (libc)Width of Type. * CHILD_MAX: (libc)General Limits. * CIGNORE: (libc)Control Modes. * CLK_TCK: (libc)Processor Time. * CLOCAL: (libc)Control Modes. * CLOCKS_PER_SEC: (libc)CPU Time. * CLOCK_MONOTONIC: (libc)Getting the Time. * CLOCK_REALTIME: (libc)Getting the Time. * COLL_WEIGHTS_MAX: (libc)Utility Limits. * CPU_CLR: (libc)CPU Affinity. * CPU_FEATURE_ACTIVE: (libc)X86. * CPU_FEATURE_PRESENT: (libc)X86. * CPU_ISSET: (libc)CPU Affinity. * CPU_SET: (libc)CPU Affinity. * CPU_SETSIZE: (libc)CPU Affinity. * CPU_ZERO: (libc)CPU Affinity. * CREAD: (libc)Control Modes. * CRTS_IFLOW: (libc)Control Modes. * CS5: (libc)Control Modes. * CS6: (libc)Control Modes. * CS7: (libc)Control Modes. * CS8: (libc)Control Modes. * CSIZE: (libc)Control Modes. * CSTOPB: (libc)Control Modes. * DLFO_EH_SEGMENT_TYPE: (libc)Dynamic Linker Introspection. * DLFO_STRUCT_HAS_EH_COUNT: (libc)Dynamic Linker Introspection. * DLFO_STRUCT_HAS_EH_DBASE: (libc)Dynamic Linker Introspection. * DTTOIF: (libc)Directory Entries. * E2BIG: (libc)Error Codes. * EACCES: (libc)Error Codes. * EADDRINUSE: (libc)Error Codes. * EADDRNOTAVAIL: (libc)Error Codes. * EADV: (libc)Error Codes. * EAFNOSUPPORT: (libc)Error Codes. * EAGAIN: (libc)Error Codes. * EALREADY: (libc)Error Codes. * EAUTH: (libc)Error Codes. * EBACKGROUND: (libc)Error Codes. * EBADE: (libc)Error Codes. * EBADF: (libc)Error Codes. * EBADFD: (libc)Error Codes. * EBADMSG: (libc)Error Codes. * EBADR: (libc)Error Codes. * EBADRPC: (libc)Error Codes. * EBADRQC: (libc)Error Codes. * EBADSLT: (libc)Error Codes. * EBFONT: (libc)Error Codes. * EBUSY: (libc)Error Codes. * ECANCELED: (libc)Error Codes. * ECHILD: (libc)Error Codes. * ECHO: (libc)Local Modes. * ECHOCTL: (libc)Local Modes. * ECHOE: (libc)Local Modes. * ECHOK: (libc)Local Modes. * ECHOKE: (libc)Local Modes. * ECHONL: (libc)Local Modes. * ECHOPRT: (libc)Local Modes. * ECHRNG: (libc)Error Codes. * ECOMM: (libc)Error Codes. * ECONNABORTED: (libc)Error Codes. * ECONNREFUSED: (libc)Error Codes. * ECONNRESET: (libc)Error Codes. * ED: (libc)Error Codes. * EDEADLK: (libc)Error Codes. * EDEADLOCK: (libc)Error Codes. * EDESTADDRREQ: (libc)Error Codes. * EDIED: (libc)Error Codes. * EDOM: (libc)Error Codes. * EDOTDOT: (libc)Error Codes. * EDQUOT: (libc)Error Codes. * EEXIST: (libc)Error Codes. * EFAULT: (libc)Error Codes. * EFBIG: (libc)Error Codes. * EFTYPE: (libc)Error Codes. * EGRATUITOUS: (libc)Error Codes. * EGREGIOUS: (libc)Error Codes. * EHOSTDOWN: (libc)Error Codes. * EHOSTUNREACH: (libc)Error Codes. * EHWPOISON: (libc)Error Codes. * EIDRM: (libc)Error Codes. * EIEIO: (libc)Error Codes. * EILSEQ: (libc)Error Codes. * EINPROGRESS: (libc)Error Codes. * EINTR: (libc)Error Codes. * EINVAL: (libc)Error Codes. * EIO: (libc)Error Codes. * EISCONN: (libc)Error Codes. * EISDIR: (libc)Error Codes. * EISNAM: (libc)Error Codes. * EKEYEXPIRED: (libc)Error Codes. * EKEYREJECTED: (libc)Error Codes. * EKEYREVOKED: (libc)Error Codes. * EL2HLT: (libc)Error Codes. * EL2NSYNC: (libc)Error Codes. * EL3HLT: (libc)Error Codes. * EL3RST: (libc)Error Codes. * ELIBACC: (libc)Error Codes. * ELIBBAD: (libc)Error Codes. * ELIBEXEC: (libc)Error Codes. * ELIBMAX: (libc)Error Codes. * ELIBSCN: (libc)Error Codes. * ELNRNG: (libc)Error Codes. * ELOOP: (libc)Error Codes. * EMEDIUMTYPE: (libc)Error Codes. * EMFILE: (libc)Error Codes. * EMLINK: (libc)Error Codes. * EMSGSIZE: (libc)Error Codes. * EMULTIHOP: (libc)Error Codes. * ENAMETOOLONG: (libc)Error Codes. * ENAVAIL: (libc)Error Codes. * ENEEDAUTH: (libc)Error Codes. * ENETDOWN: (libc)Error Codes. * ENETRESET: (libc)Error Codes. * ENETUNREACH: (libc)Error Codes. * ENFILE: (libc)Error Codes. * ENOANO: (libc)Error Codes. * ENOBUFS: (libc)Error Codes. * ENOCSI: (libc)Error Codes. * ENODATA: (libc)Error Codes. * ENODEV: (libc)Error Codes. * ENOENT: (libc)Error Codes. * ENOEXEC: (libc)Error Codes. * ENOKEY: (libc)Error Codes. * ENOLCK: (libc)Error Codes. * ENOLINK: (libc)Error Codes. * ENOMEDIUM: (libc)Error Codes. * ENOMEM: (libc)Error Codes. * ENOMSG: (libc)Error Codes. * ENONET: (libc)Error Codes. * ENOPKG: (libc)Error Codes. * ENOPROTOOPT: (libc)Error Codes. * ENOSPC: (libc)Error Codes. * ENOSR: (libc)Error Codes. * ENOSTR: (libc)Error Codes. * ENOSYS: (libc)Error Codes. * ENOTBLK: (libc)Error Codes. * ENOTCONN: (libc)Error Codes. * ENOTDIR: (libc)Error Codes. * ENOTEMPTY: (libc)Error Codes. * ENOTNAM: (libc)Error Codes. * ENOTRECOVERABLE: (libc)Error Codes. * ENOTSOCK: (libc)Error Codes. * ENOTSUP: (libc)Error Codes. * ENOTTY: (libc)Error Codes. * ENOTUNIQ: (libc)Error Codes. * ENXIO: (libc)Error Codes. * EOF: (libc)EOF and Errors. * EOPNOTSUPP: (libc)Error Codes. * EOVERFLOW: (libc)Error Codes. * EOWNERDEAD: (libc)Error Codes. * EPERM: (libc)Error Codes. * EPFNOSUPPORT: (libc)Error Codes. * EPIPE: (libc)Error Codes. * EPROCLIM: (libc)Error Codes. * EPROCUNAVAIL: (libc)Error Codes. * EPROGMISMATCH: (libc)Error Codes. * EPROGUNAVAIL: (libc)Error Codes. * EPROTO: (libc)Error Codes. * EPROTONOSUPPORT: (libc)Error Codes. * EPROTOTYPE: (libc)Error Codes. * EQUIV_CLASS_MAX: (libc)Utility Limits. * ERANGE: (libc)Error Codes. * EREMCHG: (libc)Error Codes. * EREMOTE: (libc)Error Codes. * EREMOTEIO: (libc)Error Codes. * ERESTART: (libc)Error Codes. * ERFKILL: (libc)Error Codes. * EROFS: (libc)Error Codes. * ERPCMISMATCH: (libc)Error Codes. * ESHUTDOWN: (libc)Error Codes. * ESOCKTNOSUPPORT: (libc)Error Codes. * ESPIPE: (libc)Error Codes. * ESRCH: (libc)Error Codes. * ESRMNT: (libc)Error Codes. * ESTALE: (libc)Error Codes. * ESTRPIPE: (libc)Error Codes. * ETIME: (libc)Error Codes. * ETIMEDOUT: (libc)Error Codes. * ETOOMANYREFS: (libc)Error Codes. * ETXTBSY: (libc)Error Codes. * EUCLEAN: (libc)Error Codes. * EUNATCH: (libc)Error Codes. * EUSERS: (libc)Error Codes. * EWOULDBLOCK: (libc)Error Codes. * EXDEV: (libc)Error Codes. * EXFULL: (libc)Error Codes. * EXIT_FAILURE: (libc)Exit Status. * EXIT_SUCCESS: (libc)Exit Status. * EXPR_NEST_MAX: (libc)Utility Limits. * FD_CLOEXEC: (libc)Descriptor Flags. * FD_CLR: (libc)Waiting for I/O. * FD_ISSET: (libc)Waiting for I/O. * FD_SET: (libc)Waiting for I/O. * FD_SETSIZE: (libc)Waiting for I/O. * FD_ZERO: (libc)Waiting for I/O. * FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN. * FILENAME_MAX: (libc)Limits for Files. * FLUSHO: (libc)Local Modes. * FOPEN_MAX: (libc)Opening Streams. * FP_ILOGB0: (libc)Exponents and Logarithms. * FP_ILOGBNAN: (libc)Exponents and Logarithms. * FP_LLOGB0: (libc)Exponents and Logarithms. * FP_LLOGBNAN: (libc)Exponents and Logarithms. * F_DUPFD: (libc)Duplicating Descriptors. * F_GETFD: (libc)Descriptor Flags. * F_GETFL: (libc)Getting File Status Flags. * F_GETLK: (libc)File Locks. * F_GETOWN: (libc)Interrupt Input. * F_OFD_GETLK: (libc)Open File Description Locks. * F_OFD_SETLK: (libc)Open File Description Locks. * F_OFD_SETLKW: (libc)Open File Description Locks. * F_OK: (libc)Testing File Access. * F_SETFD: (libc)Descriptor Flags. * F_SETFL: (libc)Getting File Status Flags. * F_SETLK: (libc)File Locks. * F_SETLKW: (libc)File Locks. * F_SETOWN: (libc)Interrupt Input. * HUGE_VAL: (libc)Math Error Reporting. * HUGE_VALF: (libc)Math Error Reporting. * HUGE_VALL: (libc)Math Error Reporting. * HUGE_VAL_FN: (libc)Math Error Reporting. * HUGE_VAL_FNx: (libc)Math Error Reporting. * HUPCL: (libc)Control Modes. * I: (libc)Complex Numbers. * ICANON: (libc)Local Modes. * ICRNL: (libc)Input Modes. * IEXTEN: (libc)Local Modes. * IFNAMSIZ: (libc)Interface Naming. * IFTODT: (libc)Directory Entries. * IGNBRK: (libc)Input Modes. * IGNCR: (libc)Input Modes. * IGNPAR: (libc)Input Modes. * IMAXBEL: (libc)Input Modes. * INADDR_ANY: (libc)Host Address Data Type. * INADDR_BROADCAST: (libc)Host Address Data Type. * INADDR_LOOPBACK: (libc)Host Address Data Type. * INADDR_NONE: (libc)Host Address Data Type. * INFINITY: (libc)Infinity and NaN. * INLCR: (libc)Input Modes. * INPCK: (libc)Input Modes. * IPPORT_RESERVED: (libc)Ports. * IPPORT_USERRESERVED: (libc)Ports. * ISIG: (libc)Local Modes. * ISTRIP: (libc)Input Modes. * IXANY: (libc)Input Modes. * IXOFF: (libc)Input Modes. * IXON: (libc)Input Modes. * LINE_MAX: (libc)Utility Limits. * LINK_MAX: (libc)Limits for Files. * L_ctermid: (libc)Identifying the Terminal. * L_cuserid: (libc)Who Logged In. * L_tmpnam: (libc)Temporary Files. * MAXNAMLEN: (libc)Limits for Files. * MAXSYMLINKS: (libc)Symbolic Links. * MAX_CANON: (libc)Limits for Files. * MAX_INPUT: (libc)Limits for Files. * MB_CUR_MAX: (libc)Selecting the Conversion. * MB_LEN_MAX: (libc)Selecting the Conversion. * MDMBUF: (libc)Control Modes. * MSG_DONTROUTE: (libc)Socket Data Options. * MSG_OOB: (libc)Socket Data Options. * MSG_PEEK: (libc)Socket Data Options. * NAME_MAX: (libc)Limits for Files. * NAN: (libc)Infinity and NaN. * NCCS: (libc)Mode Data Types. * NGROUPS_MAX: (libc)General Limits. * NOFLSH: (libc)Local Modes. * NOKERNINFO: (libc)Local Modes. * NSIG: (libc)Standard Signals. * NULL: (libc)Null Pointer Constant. * ONLCR: (libc)Output Modes. * ONOEOT: (libc)Output Modes. * OPEN_MAX: (libc)General Limits. * OPOST: (libc)Output Modes. * OXTABS: (libc)Output Modes. * O_ACCMODE: (libc)Access Modes. * O_APPEND: (libc)Operating Modes. * O_ASYNC: (libc)Operating Modes. * O_CREAT: (libc)Open-time Flags. * O_DIRECTORY: (libc)Open-time Flags. * O_EXCL: (libc)Open-time Flags. * O_EXEC: (libc)Access Modes. * O_EXLOCK: (libc)Open-time Flags. * O_FSYNC: (libc)Operating Modes. * O_IGNORE_CTTY: (libc)Open-time Flags. * O_NDELAY: (libc)Operating Modes. * O_NOATIME: (libc)Operating Modes. * O_NOCTTY: (libc)Open-time Flags. * O_NOFOLLOW: (libc)Open-time Flags. * O_NOLINK: (libc)Open-time Flags. * O_NONBLOCK: (libc)Open-time Flags. * O_NONBLOCK: (libc)Operating Modes. * O_NOTRANS: (libc)Open-time Flags. * O_PATH: (libc)Access Modes. * O_RDONLY: (libc)Access Modes. * O_RDWR: (libc)Access Modes. * O_READ: (libc)Access Modes. * O_SHLOCK: (libc)Open-time Flags. * O_SYNC: (libc)Operating Modes. * O_TMPFILE: (libc)Open-time Flags. * O_TRUNC: (libc)Open-time Flags. * O_WRITE: (libc)Access Modes. * O_WRONLY: (libc)Access Modes. * PARENB: (libc)Control Modes. * PARMRK: (libc)Input Modes. * PARODD: (libc)Control Modes. * PATH_MAX: (libc)Limits for Files. * PA_FLAG_MASK: (libc)Parsing a Template String. * PENDIN: (libc)Local Modes. * PF_FILE: (libc)Local Namespace Details. * PF_INET6: (libc)Internet Namespace. * PF_INET: (libc)Internet Namespace. * PF_LOCAL: (libc)Local Namespace Details. * PF_UNIX: (libc)Local Namespace Details. * PIPE_BUF: (libc)Limits for Files. * PTHREAD_ATTR_NO_SIGMASK_NP: (libc)Initial Thread Signal Mask. * P_tmpdir: (libc)Temporary Files. * RAND_MAX: (libc)ISO Random. * RE_DUP_MAX: (libc)General Limits. * RLIM_INFINITY: (libc)Limits on Resources. * RSEQ_SIG: (libc)Restartable Sequences. * R_OK: (libc)Testing File Access. * SA_NOCLDSTOP: (libc)Flags for Sigaction. * SA_NOCLDWAIT: (libc)Flags for Sigaction. * SA_NODEFER: (libc)Flags for Sigaction. * SA_ONSTACK: (libc)Flags for Sigaction. * SA_RESETHAND: (libc)Flags for Sigaction. * SA_RESTART: (libc)Flags for Sigaction. * SA_SIGINFO: (libc)Flags for Sigaction. * SEEK_CUR: (libc)File Positioning. * SEEK_END: (libc)File Positioning. * SEEK_SET: (libc)File Positioning. * SIGABRT: (libc)Program Error Signals. * SIGALRM: (libc)Alarm Signals. * SIGBUS: (libc)Program Error Signals. * SIGCHLD: (libc)Job Control Signals. * SIGCLD: (libc)Job Control Signals. * SIGCONT: (libc)Job Control Signals. * SIGEMT: (libc)Program Error Signals. * SIGFPE: (libc)Program Error Signals. * SIGHUP: (libc)Termination Signals. * SIGILL: (libc)Program Error Signals. * SIGINFO: (libc)Miscellaneous Signals. * SIGINT: (libc)Termination Signals. * SIGIO: (libc)Asynchronous I/O Signals. * SIGIOT: (libc)Program Error Signals. * SIGKILL: (libc)Termination Signals. * SIGLOST: (libc)Operation Error Signals. * SIGPIPE: (libc)Operation Error Signals. * SIGPOLL: (libc)Asynchronous I/O Signals. * SIGPROF: (libc)Alarm Signals. * SIGQUIT: (libc)Termination Signals. * SIGSEGV: (libc)Program Error Signals. * SIGSTOP: (libc)Job Control Signals. * SIGSYS: (libc)Program Error Signals. * SIGTERM: (libc)Termination Signals. * SIGTRAP: (libc)Program Error Signals. * SIGTSTP: (libc)Job Control Signals. * SIGTTIN: (libc)Job Control Signals. * SIGTTOU: (libc)Job Control Signals. * SIGURG: (libc)Asynchronous I/O Signals. * SIGUSR1: (libc)Miscellaneous Signals. * SIGUSR2: (libc)Miscellaneous Signals. * SIGVTALRM: (libc)Alarm Signals. * SIGWINCH: (libc)Miscellaneous Signals. * SIGXCPU: (libc)Operation Error Signals. * SIGXFSZ: (libc)Operation Error Signals. * SIG_ERR: (libc)Basic Signal Handling. * SNAN: (libc)Infinity and NaN. * SNANF: (libc)Infinity and NaN. * SNANFN: (libc)Infinity and NaN. * SNANFNx: (libc)Infinity and NaN. * SNANL: (libc)Infinity and NaN. * SOCK_DGRAM: (libc)Communication Styles. * SOCK_RAW: (libc)Communication Styles. * SOCK_RDM: (libc)Communication Styles. * SOCK_SEQPACKET: (libc)Communication Styles. * SOCK_STREAM: (libc)Communication Styles. * SOL_SOCKET: (libc)Socket-Level Options. * SSIZE_MAX: (libc)General Limits. * STREAM_MAX: (libc)General Limits. * SUN_LEN: (libc)Local Namespace Details. * S_IFMT: (libc)Testing File Type. * S_ISBLK: (libc)Testing File Type. * S_ISCHR: (libc)Testing File Type. * S_ISDIR: (libc)Testing File Type. * S_ISFIFO: (libc)Testing File Type. * S_ISLNK: (libc)Testing File Type. * S_ISREG: (libc)Testing File Type. * S_ISSOCK: (libc)Testing File Type. * S_TYPEISMQ: (libc)Testing File Type. * S_TYPEISSEM: (libc)Testing File Type. * S_TYPEISSHM: (libc)Testing File Type. * TIME_UTC: (libc)Getting the Time. * TMP_MAX: (libc)Temporary Files. * TOSTOP: (libc)Local Modes. * TZNAME_MAX: (libc)General Limits. * VDISCARD: (libc)Other Special. * VDSUSP: (libc)Signal Characters. * VEOF: (libc)Editing Characters. * VEOL2: (libc)Editing Characters. * VEOL: (libc)Editing Characters. * VERASE: (libc)Editing Characters. * VINTR: (libc)Signal Characters. * VKILL: (libc)Editing Characters. * VLNEXT: (libc)Other Special. * VMIN: (libc)Noncanonical Input. * VQUIT: (libc)Signal Characters. * VREPRINT: (libc)Editing Characters. * VSTART: (libc)Start/Stop Characters. * VSTATUS: (libc)Other Special. * VSTOP: (libc)Start/Stop Characters. * VSUSP: (libc)Signal Characters. * VTIME: (libc)Noncanonical Input. * VWERASE: (libc)Editing Characters. * WCHAR_MAX: (libc)Extended Char Intro. * WCHAR_MIN: (libc)Extended Char Intro. * WCOREDUMP: (libc)Process Completion Status. * WEOF: (libc)EOF and Errors. * WEOF: (libc)Extended Char Intro. * WEXITSTATUS: (libc)Process Completion Status. * WIFEXITED: (libc)Process Completion Status. * WIFSIGNALED: (libc)Process Completion Status. * WIFSTOPPED: (libc)Process Completion Status. * WSTOPSIG: (libc)Process Completion Status. * WTERMSIG: (libc)Process Completion Status. * W_OK: (libc)Testing File Access. * X_OK: (libc)Testing File Access. * _Complex_I: (libc)Complex Numbers. * _Exit: (libc)Termination Internals. * _Fork: (libc)Creating a Process. * _IOFBF: (libc)Controlling Buffering. * _IOLBF: (libc)Controlling Buffering. * _IONBF: (libc)Controlling Buffering. * _Imaginary_I: (libc)Complex Numbers. * _PATH_UTMP: (libc)Manipulating the Database. * _PATH_WTMP: (libc)Manipulating the Database. * _POSIX2_C_DEV: (libc)System Options. * _POSIX2_C_VERSION: (libc)Version Supported. * _POSIX2_FORT_DEV: (libc)System Options. * _POSIX2_FORT_RUN: (libc)System Options. * _POSIX2_LOCALEDEF: (libc)System Options. * _POSIX2_SW_DEV: (libc)System Options. * _POSIX_CHOWN_RESTRICTED: (libc)Options for Files. * _POSIX_JOB_CONTROL: (libc)System Options. * _POSIX_NO_TRUNC: (libc)Options for Files. * _POSIX_SAVED_IDS: (libc)System Options. * _POSIX_VDISABLE: (libc)Options for Files. * _POSIX_VERSION: (libc)Version Supported. * __fbufsize: (libc)Controlling Buffering. * __flbf: (libc)Controlling Buffering. * __fpending: (libc)Controlling Buffering. * __fpurge: (libc)Flushing Buffers. * __freadable: (libc)Opening Streams. * __freading: (libc)Opening Streams. * __fsetlocking: (libc)Streams and Threads. * __fwritable: (libc)Opening Streams. * __fwriting: (libc)Opening Streams. * __gconv_end_fct: (libc)glibc iconv Implementation. * __gconv_fct: (libc)glibc iconv Implementation. * __gconv_init_fct: (libc)glibc iconv Implementation. * __ppc_get_timebase: (libc)PowerPC. * __ppc_get_timebase_freq: (libc)PowerPC. * __ppc_mdoio: (libc)PowerPC. * __ppc_mdoom: (libc)PowerPC. * __ppc_set_ppr_low: (libc)PowerPC. * __ppc_set_ppr_med: (libc)PowerPC. * __ppc_set_ppr_med_high: (libc)PowerPC. * __ppc_set_ppr_med_low: (libc)PowerPC. * __ppc_set_ppr_very_low: (libc)PowerPC. * __ppc_yield: (libc)PowerPC. * __riscv_flush_icache: (libc)RISC-V. * __va_copy: (libc)Argument Macros. * __x86_get_cpuid_feature_leaf: (libc)X86. * _dl_find_object: (libc)Dynamic Linker Introspection. * _exit: (libc)Termination Internals. * _flushlbf: (libc)Flushing Buffers. * _tolower: (libc)Case Conversion. * _toupper: (libc)Case Conversion. * a64l: (libc)Encode Binary Data. * abort: (libc)Aborting a Program. * abs: (libc)Absolute Value. * accept: (libc)Accepting Connections. * access: (libc)Testing File Access. * acos: (libc)Inverse Trig Functions. * acosf: (libc)Inverse Trig Functions. * acosfN: (libc)Inverse Trig Functions. * acosfNx: (libc)Inverse Trig Functions. * acosh: (libc)Hyperbolic Functions. * acoshf: (libc)Hyperbolic Functions. * acoshfN: (libc)Hyperbolic Functions. * acoshfNx: (libc)Hyperbolic Functions. * acoshl: (libc)Hyperbolic Functions. * acosl: (libc)Inverse Trig Functions. * acospi: (libc)Inverse Trig Functions. * acospif: (libc)Inverse Trig Functions. * acospifN: (libc)Inverse Trig Functions. * acospifNx: (libc)Inverse Trig Functions. * acospil: (libc)Inverse Trig Functions. * addmntent: (libc)mtab. * addseverity: (libc)Adding Severity Classes. * adjtime: (libc)Setting and Adjusting the Time. * adjtimex: (libc)Setting and Adjusting the Time. * aio_cancel64: (libc)Cancel AIO Operations. * aio_cancel: (libc)Cancel AIO Operations. * aio_error64: (libc)Status of AIO Operations. * aio_error: (libc)Status of AIO Operations. * aio_fsync64: (libc)Synchronizing AIO Operations. * aio_fsync: (libc)Synchronizing AIO Operations. * aio_init: (libc)Configuration of AIO. * aio_read64: (libc)Asynchronous Reads/Writes. * aio_read: (libc)Asynchronous Reads/Writes. * aio_return64: (libc)Status of AIO Operations. * aio_return: (libc)Status of AIO Operations. * aio_suspend64: (libc)Synchronizing AIO Operations. * aio_suspend: (libc)Synchronizing AIO Operations. * aio_write64: (libc)Asynchronous Reads/Writes. * aio_write: (libc)Asynchronous Reads/Writes. * alarm: (libc)Setting an Alarm. * aligned_alloc: (libc)Aligned Memory Blocks. * alloca: (libc)Variable Size Automatic. * alphasort64: (libc)Scanning Directory Content. * alphasort: (libc)Scanning Directory Content. * arc4random: (libc)High Quality Random. * arc4random_buf: (libc)High Quality Random. * arc4random_uniform: (libc)High Quality Random. * argp_error: (libc)Argp Helper Functions. * argp_failure: (libc)Argp Helper Functions. * argp_help: (libc)Argp Help. * argp_parse: (libc)Argp. * argp_state_help: (libc)Argp Helper Functions. * argp_usage: (libc)Argp Helper Functions. * argz_add: (libc)Argz Functions. * argz_add_sep: (libc)Argz Functions. * argz_append: (libc)Argz Functions. * argz_count: (libc)Argz Functions. * argz_create: (libc)Argz Functions. * argz_create_sep: (libc)Argz Functions. * argz_delete: (libc)Argz Functions. * argz_extract: (libc)Argz Functions. * argz_insert: (libc)Argz Functions. * argz_next: (libc)Argz Functions. * argz_replace: (libc)Argz Functions. * argz_stringify: (libc)Argz Functions. * asctime: (libc)Formatting Calendar Time. * asctime_r: (libc)Formatting Calendar Time. * asin: (libc)Inverse Trig Functions. * asinf: (libc)Inverse Trig Functions. * asinfN: (libc)Inverse Trig Functions. * asinfNx: (libc)Inverse Trig Functions. * asinh: (libc)Hyperbolic Functions. * asinhf: (libc)Hyperbolic Functions. * asinhfN: (libc)Hyperbolic Functions. * asinhfNx: (libc)Hyperbolic Functions. * asinhl: (libc)Hyperbolic Functions. * asinl: (libc)Inverse Trig Functions. * asinpi: (libc)Inverse Trig Functions. * asinpif: (libc)Inverse Trig Functions. * asinpifN: (libc)Inverse Trig Functions. * asinpifNx: (libc)Inverse Trig Functions. * asinpil: (libc)Inverse Trig Functions. * asprintf: (libc)Dynamic Output. * assert: (libc)Consistency Checking. * assert_perror: (libc)Consistency Checking. * atan2: (libc)Inverse Trig Functions. * atan2f: (libc)Inverse Trig Functions. * atan2fN: (libc)Inverse Trig Functions. * atan2fNx: (libc)Inverse Trig Functions. * atan2l: (libc)Inverse Trig Functions. * atan2pi: (libc)Inverse Trig Functions. * atan2pif: (libc)Inverse Trig Functions. * atan2pifN: (libc)Inverse Trig Functions. * atan2pifNx: (libc)Inverse Trig Functions. * atan2pil: (libc)Inverse Trig Functions. * atan: (libc)Inverse Trig Functions. * atanf: (libc)Inverse Trig Functions. * atanfN: (libc)Inverse Trig Functions. * atanfNx: (libc)Inverse Trig Functions. * atanh: (libc)Hyperbolic Functions. * atanhf: (libc)Hyperbolic Functions. * atanhfN: (libc)Hyperbolic Functions. * atanhfNx: (libc)Hyperbolic Functions. * atanhl: (libc)Hyperbolic Functions. * atanl: (libc)Inverse Trig Functions. * atanpi: (libc)Inverse Trig Functions. * atanpif: (libc)Inverse Trig Functions. * atanpifN: (libc)Inverse Trig Functions. * atanpifNx: (libc)Inverse Trig Functions. * atanpil: (libc)Inverse Trig Functions. * atexit: (libc)Cleanups on Exit. * atof: (libc)Parsing of Floats. * atoi: (libc)Parsing of Integers. * atol: (libc)Parsing of Integers. * atoll: (libc)Parsing of Integers. * backtrace: (libc)Backtraces. * backtrace_symbols: (libc)Backtraces. * backtrace_symbols_fd: (libc)Backtraces. * basename: (libc)Finding Tokens in a String. * basename: (libc)Finding Tokens in a String. * bcmp: (libc)String/Array Comparison. * bcopy: (libc)Copying Strings and Arrays. * bind: (libc)Setting Address. * bind_textdomain_codeset: (libc)Charset conversion in gettext. * bindtextdomain: (libc)Locating gettext catalog. * brk: (libc)Resizing the Data Segment. * bsearch: (libc)Array Search Function. * btowc: (libc)Converting a Character. * bzero: (libc)Copying Strings and Arrays. * cabs: (libc)Absolute Value. * cabsf: (libc)Absolute Value. * cabsfN: (libc)Absolute Value. * cabsfNx: (libc)Absolute Value. * cabsl: (libc)Absolute Value. * cacos: (libc)Inverse Trig Functions. * cacosf: (libc)Inverse Trig Functions. * cacosfN: (libc)Inverse Trig Functions. * cacosfNx: (libc)Inverse Trig Functions. * cacosh: (libc)Hyperbolic Functions. * cacoshf: (libc)Hyperbolic Functions. * cacoshfN: (libc)Hyperbolic Functions. * cacoshfNx: (libc)Hyperbolic Functions. * cacoshl: (libc)Hyperbolic Functions. * cacosl: (libc)Inverse Trig Functions. * call_once: (libc)Call Once. * calloc: (libc)Allocating Cleared Space. * canonicalize: (libc)FP Bit Twiddling. * canonicalize_file_name: (libc)Symbolic Links. * canonicalizef: (libc)FP Bit Twiddling. * canonicalizefN: (libc)FP Bit Twiddling. * canonicalizefNx: (libc)FP Bit Twiddling. * canonicalizel: (libc)FP Bit Twiddling. * carg: (libc)Operations on Complex. * cargf: (libc)Operations on Complex. * cargfN: (libc)Operations on Complex. * cargfNx: (libc)Operations on Complex. * cargl: (libc)Operations on Complex. * casin: (libc)Inverse Trig Functions. * casinf: (libc)Inverse Trig Functions. * casinfN: (libc)Inverse Trig Functions. * casinfNx: (libc)Inverse Trig Functions. * casinh: (libc)Hyperbolic Functions. * casinhf: (libc)Hyperbolic Functions. * casinhfN: (libc)Hyperbolic Functions. * casinhfNx: (libc)Hyperbolic Functions. * casinhl: (libc)Hyperbolic Functions. * casinl: (libc)Inverse Trig Functions. * catan: (libc)Inverse Trig Functions. * catanf: (libc)Inverse Trig Functions. * catanfN: (libc)Inverse Trig Functions. * catanfNx: (libc)Inverse Trig Functions. * catanh: (libc)Hyperbolic Functions. * catanhf: (libc)Hyperbolic Functions. * catanhfN: (libc)Hyperbolic Functions. * catanhfNx: (libc)Hyperbolic Functions. * catanhl: (libc)Hyperbolic Functions. * catanl: (libc)Inverse Trig Functions. * catclose: (libc)The catgets Functions. * catgets: (libc)The catgets Functions. * catopen: (libc)The catgets Functions. * cbrt: (libc)Exponents and Logarithms. * cbrtf: (libc)Exponents and Logarithms. * cbrtfN: (libc)Exponents and Logarithms. * cbrtfNx: (libc)Exponents and Logarithms. * cbrtl: (libc)Exponents and Logarithms. * ccos: (libc)Trig Functions. * ccosf: (libc)Trig Functions. * ccosfN: (libc)Trig Functions. * ccosfNx: (libc)Trig Functions. * ccosh: (libc)Hyperbolic Functions. * ccoshf: (libc)Hyperbolic Functions. * ccoshfN: (libc)Hyperbolic Functions. * ccoshfNx: (libc)Hyperbolic Functions. * ccoshl: (libc)Hyperbolic Functions. * ccosl: (libc)Trig Functions. * ceil: (libc)Rounding Functions. * ceilf: (libc)Rounding Functions. * ceilfN: (libc)Rounding Functions. * ceilfNx: (libc)Rounding Functions. * ceill: (libc)Rounding Functions. * cexp: (libc)Exponents and Logarithms. * cexpf: (libc)Exponents and Logarithms. * cexpfN: (libc)Exponents and Logarithms. * cexpfNx: (libc)Exponents and Logarithms. * cexpl: (libc)Exponents and Logarithms. * cfgetispeed: (libc)Line Speed. * cfgetospeed: (libc)Line Speed. * cfmakeraw: (libc)Noncanonical Input. * cfsetispeed: (libc)Line Speed. * cfsetospeed: (libc)Line Speed. * cfsetspeed: (libc)Line Speed. * chdir: (libc)Working Directory. * chmod: (libc)Setting Permissions. * chown: (libc)File Owner. * cimag: (libc)Operations on Complex. * cimagf: (libc)Operations on Complex. * cimagfN: (libc)Operations on Complex. * cimagfNx: (libc)Operations on Complex. * cimagl: (libc)Operations on Complex. * clearenv: (libc)Environment Access. * clearerr: (libc)Error Recovery. * clearerr_unlocked: (libc)Error Recovery. * clock: (libc)CPU Time. * clock_getres: (libc)Getting the Time. * clock_gettime: (libc)Getting the Time. * clock_settime: (libc)Setting and Adjusting the Time. * clog10: (libc)Exponents and Logarithms. * clog10f: (libc)Exponents and Logarithms. * clog10fN: (libc)Exponents and Logarithms. * clog10fNx: (libc)Exponents and Logarithms. * clog10l: (libc)Exponents and Logarithms. * clog: (libc)Exponents and Logarithms. * clogf: (libc)Exponents and Logarithms. * clogfN: (libc)Exponents and Logarithms. * clogfNx: (libc)Exponents and Logarithms. * clogl: (libc)Exponents and Logarithms. * close: (libc)Opening and Closing Files. * close_range: (libc)Opening and Closing Files. * closedir: (libc)Reading/Closing Directory. * closefrom: (libc)Opening and Closing Files. * closelog: (libc)closelog. * cnd_broadcast: (libc)ISO C Condition Variables. * cnd_destroy: (libc)ISO C Condition Variables. * cnd_init: (libc)ISO C Condition Variables. * cnd_signal: (libc)ISO C Condition Variables. * cnd_timedwait: (libc)ISO C Condition Variables. * cnd_wait: (libc)ISO C Condition Variables. * confstr: (libc)String Parameters. * conj: (libc)Operations on Complex. * conjf: (libc)Operations on Complex. * conjfN: (libc)Operations on Complex. * conjfNx: (libc)Operations on Complex. * conjl: (libc)Operations on Complex. * connect: (libc)Connecting. * copy_file_range: (libc)Copying File Data. * copysign: (libc)FP Bit Twiddling. * copysignf: (libc)FP Bit Twiddling. * copysignfN: (libc)FP Bit Twiddling. * copysignfNx: (libc)FP Bit Twiddling. * copysignl: (libc)FP Bit Twiddling. * cos: (libc)Trig Functions. * cosf: (libc)Trig Functions. * cosfN: (libc)Trig Functions. * cosfNx: (libc)Trig Functions. * cosh: (libc)Hyperbolic Functions. * coshf: (libc)Hyperbolic Functions. * coshfN: (libc)Hyperbolic Functions. * coshfNx: (libc)Hyperbolic Functions. * coshl: (libc)Hyperbolic Functions. * cosl: (libc)Trig Functions. * cospi: (libc)Trig Functions. * cospif: (libc)Trig Functions. * cospifN: (libc)Trig Functions. * cospifNx: (libc)Trig Functions. * cospil: (libc)Trig Functions. * cpow: (libc)Exponents and Logarithms. * cpowf: (libc)Exponents and Logarithms. * cpowfN: (libc)Exponents and Logarithms. * cpowfNx: (libc)Exponents and Logarithms. * cpowl: (libc)Exponents and Logarithms. * cproj: (libc)Operations on Complex. * cprojf: (libc)Operations on Complex. * cprojfN: (libc)Operations on Complex. * cprojfNx: (libc)Operations on Complex. * cprojl: (libc)Operations on Complex. * creal: (libc)Operations on Complex. * crealf: (libc)Operations on Complex. * crealfN: (libc)Operations on Complex. * crealfNx: (libc)Operations on Complex. * creall: (libc)Operations on Complex. * creat64: (libc)Opening and Closing Files. * creat: (libc)Opening and Closing Files. * csin: (libc)Trig Functions. * csinf: (libc)Trig Functions. * csinfN: (libc)Trig Functions. * csinfNx: (libc)Trig Functions. * csinh: (libc)Hyperbolic Functions. * csinhf: (libc)Hyperbolic Functions. * csinhfN: (libc)Hyperbolic Functions. * csinhfNx: (libc)Hyperbolic Functions. * csinhl: (libc)Hyperbolic Functions. * csinl: (libc)Trig Functions. * csqrt: (libc)Exponents and Logarithms. * csqrtf: (libc)Exponents and Logarithms. * csqrtfN: (libc)Exponents and Logarithms. * csqrtfNx: (libc)Exponents and Logarithms. * csqrtl: (libc)Exponents and Logarithms. * ctan: (libc)Trig Functions. * ctanf: (libc)Trig Functions. * ctanfN: (libc)Trig Functions. * ctanfNx: (libc)Trig Functions. * ctanh: (libc)Hyperbolic Functions. * ctanhf: (libc)Hyperbolic Functions. * ctanhfN: (libc)Hyperbolic Functions. * ctanhfNx: (libc)Hyperbolic Functions. * ctanhl: (libc)Hyperbolic Functions. * ctanl: (libc)Trig Functions. * ctermid: (libc)Identifying the Terminal. * ctime: (libc)Formatting Calendar Time. * ctime_r: (libc)Formatting Calendar Time. * cuserid: (libc)Who Logged In. * daddl: (libc)Misc FP Arithmetic. * dcgettext: (libc)Translation with gettext. * dcngettext: (libc)Advanced gettext functions. * ddivl: (libc)Misc FP Arithmetic. * dfmal: (libc)Misc FP Arithmetic. * dgettext: (libc)Translation with gettext. * difftime: (libc)Calculating Elapsed Time. * dirfd: (libc)Opening a Directory. * dirname: (libc)Finding Tokens in a String. * div: (libc)Integer Division. * dlinfo: (libc)Dynamic Linker Introspection. * dmull: (libc)Misc FP Arithmetic. * dngettext: (libc)Advanced gettext functions. * dprintf: (libc)Formatted Output Functions. * drand48: (libc)SVID Random. * drand48_r: (libc)SVID Random. * drem: (libc)Remainder Functions. * dremf: (libc)Remainder Functions. * dreml: (libc)Remainder Functions. * dsqrtl: (libc)Misc FP Arithmetic. * dsubl: (libc)Misc FP Arithmetic. * dup2: (libc)Duplicating Descriptors. * dup3: (libc)Duplicating Descriptors. * dup: (libc)Duplicating Descriptors. * ecvt: (libc)System V Number Conversion. * ecvt_r: (libc)System V Number Conversion. * endfsent: (libc)fstab. * endgrent: (libc)Scanning All Groups. * endhostent: (libc)Host Names. * endmntent: (libc)mtab. * endnetent: (libc)Networks Database. * endnetgrent: (libc)Lookup Netgroup. * endprotoent: (libc)Protocols Database. * endpwent: (libc)Scanning All Users. * endservent: (libc)Services Database. * endutent: (libc)Manipulating the Database. * endutxent: (libc)XPG Functions. * envz_add: (libc)Envz Functions. * envz_entry: (libc)Envz Functions. * envz_get: (libc)Envz Functions. * envz_merge: (libc)Envz Functions. * envz_remove: (libc)Envz Functions. * envz_strip: (libc)Envz Functions. * epoll_create: (libc)Other Low-Level I/O APIs. * epoll_wait: (libc)Other Low-Level I/O APIs. * erand48: (libc)SVID Random. * erand48_r: (libc)SVID Random. * erf: (libc)Special Functions. * erfc: (libc)Special Functions. * erfcf: (libc)Special Functions. * erfcfN: (libc)Special Functions. * erfcfNx: (libc)Special Functions. * erfcl: (libc)Special Functions. * erff: (libc)Special Functions. * erffN: (libc)Special Functions. * erffNx: (libc)Special Functions. * erfl: (libc)Special Functions. * err: (libc)Error Messages. * errno: (libc)Checking for Errors. * error: (libc)Error Messages. * error_at_line: (libc)Error Messages. * errx: (libc)Error Messages. * execl: (libc)Executing a File. * execle: (libc)Executing a File. * execlp: (libc)Executing a File. * execv: (libc)Executing a File. * execve: (libc)Executing a File. * execvp: (libc)Executing a File. * exit: (libc)Normal Termination. * exp10: (libc)Exponents and Logarithms. * exp10f: (libc)Exponents and Logarithms. * exp10fN: (libc)Exponents and Logarithms. * exp10fNx: (libc)Exponents and Logarithms. * exp10l: (libc)Exponents and Logarithms. * exp10m1: (libc)Exponents and Logarithms. * exp10m1f: (libc)Exponents and Logarithms. * exp10m1fN: (libc)Exponents and Logarithms. * exp10m1fNx: (libc)Exponents and Logarithms. * exp10m1l: (libc)Exponents and Logarithms. * exp2: (libc)Exponents and Logarithms. * exp2f: (libc)Exponents and Logarithms. * exp2fN: (libc)Exponents and Logarithms. * exp2fNx: (libc)Exponents and Logarithms. * exp2l: (libc)Exponents and Logarithms. * exp2m1: (libc)Exponents and Logarithms. * exp2m1f: (libc)Exponents and Logarithms. * exp2m1fN: (libc)Exponents and Logarithms. * exp2m1fNx: (libc)Exponents and Logarithms. * exp2m1l: (libc)Exponents and Logarithms. * exp: (libc)Exponents and Logarithms. * expf: (libc)Exponents and Logarithms. * expfN: (libc)Exponents and Logarithms. * expfNx: (libc)Exponents and Logarithms. * expl: (libc)Exponents and Logarithms. * explicit_bzero: (libc)Erasing Sensitive Data. * expm1: (libc)Exponents and Logarithms. * expm1f: (libc)Exponents and Logarithms. * expm1fN: (libc)Exponents and Logarithms. * expm1fNx: (libc)Exponents and Logarithms. * expm1l: (libc)Exponents and Logarithms. * fMaddfN: (libc)Misc FP Arithmetic. * fMaddfNx: (libc)Misc FP Arithmetic. * fMdivfN: (libc)Misc FP Arithmetic. * fMdivfNx: (libc)Misc FP Arithmetic. * fMfmafN: (libc)Misc FP Arithmetic. * fMfmafNx: (libc)Misc FP Arithmetic. * fMmulfN: (libc)Misc FP Arithmetic. * fMmulfNx: (libc)Misc FP Arithmetic. * fMsqrtfN: (libc)Misc FP Arithmetic. * fMsqrtfNx: (libc)Misc FP Arithmetic. * fMsubfN: (libc)Misc FP Arithmetic. * fMsubfNx: (libc)Misc FP Arithmetic. * fMxaddfN: (libc)Misc FP Arithmetic. * fMxaddfNx: (libc)Misc FP Arithmetic. * fMxdivfN: (libc)Misc FP Arithmetic. * fMxdivfNx: (libc)Misc FP Arithmetic. * fMxfmafN: (libc)Misc FP Arithmetic. * fMxfmafNx: (libc)Misc FP Arithmetic. * fMxmulfN: (libc)Misc FP Arithmetic. * fMxmulfNx: (libc)Misc FP Arithmetic. * fMxsqrtfN: (libc)Misc FP Arithmetic. * fMxsqrtfNx: (libc)Misc FP Arithmetic. * fMxsubfN: (libc)Misc FP Arithmetic. * fMxsubfNx: (libc)Misc FP Arithmetic. * fabs: (libc)Absolute Value. * fabsf: (libc)Absolute Value. * fabsfN: (libc)Absolute Value. * fabsfNx: (libc)Absolute Value. * fabsl: (libc)Absolute Value. * fadd: (libc)Misc FP Arithmetic. * faddl: (libc)Misc FP Arithmetic. * fchdir: (libc)Working Directory. * fchmod: (libc)Setting Permissions. * fchown: (libc)File Owner. * fclose: (libc)Closing Streams. * fcloseall: (libc)Closing Streams. * fcntl: (libc)Control Operations. * fcvt: (libc)System V Number Conversion. * fcvt_r: (libc)System V Number Conversion. * fdatasync: (libc)Synchronizing I/O. * fdim: (libc)Misc FP Arithmetic. * fdimf: (libc)Misc FP Arithmetic. * fdimfN: (libc)Misc FP Arithmetic. * fdimfNx: (libc)Misc FP Arithmetic. * fdiml: (libc)Misc FP Arithmetic. * fdiv: (libc)Misc FP Arithmetic. * fdivl: (libc)Misc FP Arithmetic. * fdopen: (libc)Descriptors and Streams. * fdopendir: (libc)Opening a Directory. * feclearexcept: (libc)Status bit operations. * fedisableexcept: (libc)Control Functions. * feenableexcept: (libc)Control Functions. * fegetenv: (libc)Control Functions. * fegetexcept: (libc)Control Functions. * fegetexceptflag: (libc)Status bit operations. * fegetmode: (libc)Control Functions. * fegetround: (libc)Rounding. * feholdexcept: (libc)Control Functions. * feof: (libc)EOF and Errors. * feof_unlocked: (libc)EOF and Errors. * feraiseexcept: (libc)Status bit operations. * ferror: (libc)EOF and Errors. * ferror_unlocked: (libc)EOF and Errors. * fesetenv: (libc)Control Functions. * fesetexcept: (libc)Status bit operations. * fesetexceptflag: (libc)Status bit operations. * fesetmode: (libc)Control Functions. * fesetround: (libc)Rounding. * fetestexcept: (libc)Status bit operations. * fetestexceptflag: (libc)Status bit operations. * feupdateenv: (libc)Control Functions. * fexecve: (libc)Executing a File. * fflush: (libc)Flushing Buffers. * fflush_unlocked: (libc)Flushing Buffers. * ffma: (libc)Misc FP Arithmetic. * ffmal: (libc)Misc FP Arithmetic. * fgetc: (libc)Character Input. * fgetc_unlocked: (libc)Character Input. * fgetgrent: (libc)Scanning All Groups. * fgetgrent_r: (libc)Scanning All Groups. * fgetpos64: (libc)Portable Positioning. * fgetpos: (libc)Portable Positioning. * fgetpwent: (libc)Scanning All Users. * fgetpwent_r: (libc)Scanning All Users. * fgets: (libc)Line Input. * fgets_unlocked: (libc)Line Input. * fgetwc: (libc)Character Input. * fgetwc_unlocked: (libc)Character Input. * fgetws: (libc)Line Input. * fgetws_unlocked: (libc)Line Input. * fileno: (libc)Descriptors and Streams. * fileno_unlocked: (libc)Descriptors and Streams. * finite: (libc)Floating Point Classes. * finitef: (libc)Floating Point Classes. * finitel: (libc)Floating Point Classes. * flockfile: (libc)Streams and Threads. * floor: (libc)Rounding Functions. * floorf: (libc)Rounding Functions. * floorfN: (libc)Rounding Functions. * floorfNx: (libc)Rounding Functions. * floorl: (libc)Rounding Functions. * fma: (libc)Misc FP Arithmetic. * fmaf: (libc)Misc FP Arithmetic. * fmafN: (libc)Misc FP Arithmetic. * fmafNx: (libc)Misc FP Arithmetic. * fmal: (libc)Misc FP Arithmetic. * fmax: (libc)Misc FP Arithmetic. * fmaxf: (libc)Misc FP Arithmetic. * fmaxfN: (libc)Misc FP Arithmetic. * fmaxfNx: (libc)Misc FP Arithmetic. * fmaximum: (libc)Misc FP Arithmetic. * fmaximum_mag: (libc)Misc FP Arithmetic. * fmaximum_mag_num: (libc)Misc FP Arithmetic. * fmaximum_mag_numf: (libc)Misc FP Arithmetic. * fmaximum_mag_numfN: (libc)Misc FP Arithmetic. * fmaximum_mag_numfNx: (libc)Misc FP Arithmetic. * fmaximum_mag_numl: (libc)Misc FP Arithmetic. * fmaximum_magf: (libc)Misc FP Arithmetic. * fmaximum_magfN: (libc)Misc FP Arithmetic. * fmaximum_magfNx: (libc)Misc FP Arithmetic. * fmaximum_magl: (libc)Misc FP Arithmetic. * fmaximum_num: (libc)Misc FP Arithmetic. * fmaximum_numf: (libc)Misc FP Arithmetic. * fmaximum_numfN: (libc)Misc FP Arithmetic. * fmaximum_numfNx: (libc)Misc FP Arithmetic. * fmaximum_numl: (libc)Misc FP Arithmetic. * fmaximumf: (libc)Misc FP Arithmetic. * fmaximumfN: (libc)Misc FP Arithmetic. * fmaximumfNx: (libc)Misc FP Arithmetic. * fmaximuml: (libc)Misc FP Arithmetic. * fmaxl: (libc)Misc FP Arithmetic. * fmaxmag: (libc)Misc FP Arithmetic. * fmaxmagf: (libc)Misc FP Arithmetic. * fmaxmagfN: (libc)Misc FP Arithmetic. * fmaxmagfNx: (libc)Misc FP Arithmetic. * fmaxmagl: (libc)Misc FP Arithmetic. * fmemopen: (libc)String Streams. * fmin: (libc)Misc FP Arithmetic. * fminf: (libc)Misc FP Arithmetic. * fminfN: (libc)Misc FP Arithmetic. * fminfNx: (libc)Misc FP Arithmetic. * fminimum: (libc)Misc FP Arithmetic. * fminimum_mag: (libc)Misc FP Arithmetic. * fminimum_mag_num: (libc)Misc FP Arithmetic. * fminimum_mag_numf: (libc)Misc FP Arithmetic. * fminimum_mag_numfN: (libc)Misc FP Arithmetic. * fminimum_mag_numfNx: (libc)Misc FP Arithmetic. * fminimum_mag_numl: (libc)Misc FP Arithmetic. * fminimum_magf: (libc)Misc FP Arithmetic. * fminimum_magfN: (libc)Misc FP Arithmetic. * fminimum_magfNx: (libc)Misc FP Arithmetic. * fminimum_magl: (libc)Misc FP Arithmetic. * fminimum_num: (libc)Misc FP Arithmetic. * fminimum_numf: (libc)Misc FP Arithmetic. * fminimum_numfN: (libc)Misc FP Arithmetic. * fminimum_numfNx: (libc)Misc FP Arithmetic. * fminimum_numl: (libc)Misc FP Arithmetic. * fminimumf: (libc)Misc FP Arithmetic. * fminimumfN: (libc)Misc FP Arithmetic. * fminimumfNx: (libc)Misc FP Arithmetic. * fminimuml: (libc)Misc FP Arithmetic. * fminl: (libc)Misc FP Arithmetic. * fminmag: (libc)Misc FP Arithmetic. * fminmagf: (libc)Misc FP Arithmetic. * fminmagfN: (libc)Misc FP Arithmetic. * fminmagfNx: (libc)Misc FP Arithmetic. * fminmagl: (libc)Misc FP Arithmetic. * fmod: (libc)Remainder Functions. * fmodf: (libc)Remainder Functions. * fmodfN: (libc)Remainder Functions. * fmodfNx: (libc)Remainder Functions. * fmodl: (libc)Remainder Functions. * fmtmsg: (libc)Printing Formatted Messages. * fmul: (libc)Misc FP Arithmetic. * fmull: (libc)Misc FP Arithmetic. * fnmatch: (libc)Wildcard Matching. * fopen64: (libc)Opening Streams. * fopen: (libc)Opening Streams. * fopencookie: (libc)Streams and Cookies. * fork: (libc)Creating a Process. * forkpty: (libc)Pseudo-Terminal Pairs. * fpathconf: (libc)Pathconf. * fpclassify: (libc)Floating Point Classes. * fprintf: (libc)Formatted Output Functions. * fputc: (libc)Simple Output. * fputc_unlocked: (libc)Simple Output. * fputs: (libc)Simple Output. * fputs_unlocked: (libc)Simple Output. * fputwc: (libc)Simple Output. * fputwc_unlocked: (libc)Simple Output. * fputws: (libc)Simple Output. * fputws_unlocked: (libc)Simple Output. * fread: (libc)Block Input/Output. * fread_unlocked: (libc)Block Input/Output. * free: (libc)Freeing after Malloc. * freopen64: (libc)Opening Streams. * freopen: (libc)Opening Streams. * frexp: (libc)Normalization Functions. * frexpf: (libc)Normalization Functions. * frexpfN: (libc)Normalization Functions. * frexpfNx: (libc)Normalization Functions. * frexpl: (libc)Normalization Functions. * fromfp: (libc)Rounding Functions. * fromfpf: (libc)Rounding Functions. * fromfpfN: (libc)Rounding Functions. * fromfpfNx: (libc)Rounding Functions. * fromfpl: (libc)Rounding Functions. * fromfpx: (libc)Rounding Functions. * fromfpxf: (libc)Rounding Functions. * fromfpxfN: (libc)Rounding Functions. * fromfpxfNx: (libc)Rounding Functions. * fromfpxl: (libc)Rounding Functions. * fscanf: (libc)Formatted Input Functions. * fseek: (libc)File Positioning. * fseeko64: (libc)File Positioning. * fseeko: (libc)File Positioning. * fsetpos64: (libc)Portable Positioning. * fsetpos: (libc)Portable Positioning. * fsqrt: (libc)Misc FP Arithmetic. * fsqrtl: (libc)Misc FP Arithmetic. * fstat64: (libc)Reading Attributes. * fstat: (libc)Reading Attributes. * fstatat64: (libc)Reading Attributes. * fstatat: (libc)Reading Attributes. * fsub: (libc)Misc FP Arithmetic. * fsubl: (libc)Misc FP Arithmetic. * fsync: (libc)Synchronizing I/O. * ftell: (libc)File Positioning. * ftello64: (libc)File Positioning. * ftello: (libc)File Positioning. * ftruncate64: (libc)File Size. * ftruncate: (libc)File Size. * ftrylockfile: (libc)Streams and Threads. * ftw64: (libc)Working with Directory Trees. * ftw: (libc)Working with Directory Trees. * funlockfile: (libc)Streams and Threads. * futimes: (libc)File Times. * fwide: (libc)Streams and I18N. * fwprintf: (libc)Formatted Output Functions. * fwrite: (libc)Block Input/Output. * fwrite_unlocked: (libc)Block Input/Output. * fwscanf: (libc)Formatted Input Functions. * gamma: (libc)Special Functions. * gammaf: (libc)Special Functions. * gammal: (libc)Special Functions. * gcvt: (libc)System V Number Conversion. * get_avphys_pages: (libc)Query Memory Parameters. * get_current_dir_name: (libc)Working Directory. * get_nprocs: (libc)Processor Resources. * get_nprocs_conf: (libc)Processor Resources. * get_phys_pages: (libc)Query Memory Parameters. * getauxval: (libc)Auxiliary Vector. * getc: (libc)Character Input. * getc_unlocked: (libc)Character Input. * getchar: (libc)Character Input. * getchar_unlocked: (libc)Character Input. * getcontext: (libc)System V contexts. * getcpu: (libc)CPU Affinity. * getcwd: (libc)Working Directory. * getdate: (libc)General Time String Parsing. * getdate_r: (libc)General Time String Parsing. * getdelim: (libc)Line Input. * getdents64: (libc)Low-level Directory Access. * getdomainnname: (libc)Host Identification. * getegid: (libc)Reading Persona. * getentropy: (libc)Unpredictable Bytes. * getenv: (libc)Environment Access. * geteuid: (libc)Reading Persona. * getfsent: (libc)fstab. * getfsfile: (libc)fstab. * getfsspec: (libc)fstab. * getgid: (libc)Reading Persona. * getgrent: (libc)Scanning All Groups. * getgrent_r: (libc)Scanning All Groups. * getgrgid: (libc)Lookup Group. * getgrgid_r: (libc)Lookup Group. * getgrnam: (libc)Lookup Group. * getgrnam_r: (libc)Lookup Group. * getgrouplist: (libc)Setting Groups. * getgroups: (libc)Reading Persona. * gethostbyaddr: (libc)Host Names. * gethostbyaddr_r: (libc)Host Names. * gethostbyname2: (libc)Host Names. * gethostbyname2_r: (libc)Host Names. * gethostbyname: (libc)Host Names. * gethostbyname_r: (libc)Host Names. * gethostent: (libc)Host Names. * gethostid: (libc)Host Identification. * gethostname: (libc)Host Identification. * getitimer: (libc)Setting an Alarm. * getline: (libc)Line Input. * getloadavg: (libc)Processor Resources. * getlogin: (libc)Who Logged In. * getmntent: (libc)mtab. * getmntent_r: (libc)mtab. * getnetbyaddr: (libc)Networks Database. * getnetbyname: (libc)Networks Database. * getnetent: (libc)Networks Database. * getnetgrent: (libc)Lookup Netgroup. * getnetgrent_r: (libc)Lookup Netgroup. * getopt: (libc)Using Getopt. * getopt_long: (libc)Getopt Long Options. * getopt_long_only: (libc)Getopt Long Options. * getpagesize: (libc)Query Memory Parameters. * getpass: (libc)getpass. * getpayload: (libc)FP Bit Twiddling. * getpayloadf: (libc)FP Bit Twiddling. * getpayloadfN: (libc)FP Bit Twiddling. * getpayloadfNx: (libc)FP Bit Twiddling. * getpayloadl: (libc)FP Bit Twiddling. * getpeername: (libc)Who is Connected. * getpgid: (libc)Process Group Functions. * getpgrp: (libc)Process Group Functions. * getpid: (libc)Process Identification. * getppid: (libc)Process Identification. * getpriority: (libc)Traditional Scheduling Functions. * getprotobyname: (libc)Protocols Database. * getprotobynumber: (libc)Protocols Database. * getprotoent: (libc)Protocols Database. * getpt: (libc)Allocation. * getpwent: (libc)Scanning All Users. * getpwent_r: (libc)Scanning All Users. * getpwnam: (libc)Lookup User. * getpwnam_r: (libc)Lookup User. * getpwuid: (libc)Lookup User. * getpwuid_r: (libc)Lookup User. * getrandom: (libc)Unpredictable Bytes. * getrlimit64: (libc)Limits on Resources. * getrlimit: (libc)Limits on Resources. * getrusage: (libc)Resource Usage. * gets: (libc)Line Input. * getservbyname: (libc)Services Database. * getservbyport: (libc)Services Database. * getservent: (libc)Services Database. * getsid: (libc)Process Group Functions. * getsockname: (libc)Reading Address. * getsockopt: (libc)Socket Option Functions. * getsubopt: (libc)Suboptions. * gettext: (libc)Translation with gettext. * gettid: (libc)Process Identification. * gettimeofday: (libc)Getting the Time. * getuid: (libc)Reading Persona. * getumask: (libc)Setting Permissions. * getutent: (libc)Manipulating the Database. * getutent_r: (libc)Manipulating the Database. * getutid: (libc)Manipulating the Database. * getutid_r: (libc)Manipulating the Database. * getutline: (libc)Manipulating the Database. * getutline_r: (libc)Manipulating the Database. * getutmp: (libc)XPG Functions. * getutmpx: (libc)XPG Functions. * getutxent: (libc)XPG Functions. * getutxid: (libc)XPG Functions. * getutxline: (libc)XPG Functions. * getw: (libc)Character Input. * getwc: (libc)Character Input. * getwc_unlocked: (libc)Character Input. * getwchar: (libc)Character Input. * getwchar_unlocked: (libc)Character Input. * getwd: (libc)Working Directory. * glob64: (libc)Calling Glob. * glob: (libc)Calling Glob. * globfree64: (libc)More Flags for Globbing. * globfree: (libc)More Flags for Globbing. * gmtime: (libc)Broken-down Time. * gmtime_r: (libc)Broken-down Time. * grantpt: (libc)Allocation. * gsignal: (libc)Signaling Yourself. * gtty: (libc)BSD Terminal Modes. * hasmntopt: (libc)mtab. * hcreate: (libc)Hash Search Function. * hcreate_r: (libc)Hash Search Function. * hdestroy: (libc)Hash Search Function. * hdestroy_r: (libc)Hash Search Function. * hsearch: (libc)Hash Search Function. * hsearch_r: (libc)Hash Search Function. * htonl: (libc)Byte Order. * htons: (libc)Byte Order. * hypot: (libc)Exponents and Logarithms. * hypotf: (libc)Exponents and Logarithms. * hypotfN: (libc)Exponents and Logarithms. * hypotfNx: (libc)Exponents and Logarithms. * hypotl: (libc)Exponents and Logarithms. * iconv: (libc)Generic Conversion Interface. * iconv_close: (libc)Generic Conversion Interface. * iconv_open: (libc)Generic Conversion Interface. * if_freenameindex: (libc)Interface Naming. * if_indextoname: (libc)Interface Naming. * if_nameindex: (libc)Interface Naming. * if_nametoindex: (libc)Interface Naming. * ilogb: (libc)Exponents and Logarithms. * ilogbf: (libc)Exponents and Logarithms. * ilogbfN: (libc)Exponents and Logarithms. * ilogbfNx: (libc)Exponents and Logarithms. * ilogbl: (libc)Exponents and Logarithms. * imaxabs: (libc)Absolute Value. * imaxdiv: (libc)Integer Division. * in6addr_any: (libc)Host Address Data Type. * in6addr_loopback: (libc)Host Address Data Type. * index: (libc)Search Functions. * inet_addr: (libc)Host Address Functions. * inet_aton: (libc)Host Address Functions. * inet_lnaof: (libc)Host Address Functions. * inet_makeaddr: (libc)Host Address Functions. * inet_netof: (libc)Host Address Functions. * inet_network: (libc)Host Address Functions. * inet_ntoa: (libc)Host Address Functions. * inet_ntop: (libc)Host Address Functions. * inet_pton: (libc)Host Address Functions. * initgroups: (libc)Setting Groups. * initstate: (libc)BSD Random. * initstate_r: (libc)BSD Random. * innetgr: (libc)Netgroup Membership. * ioctl: (libc)IOCTLs. * isalnum: (libc)Classification of Characters. * isalpha: (libc)Classification of Characters. * isascii: (libc)Classification of Characters. * isatty: (libc)Is It a Terminal. * isblank: (libc)Classification of Characters. * iscanonical: (libc)Floating Point Classes. * iscntrl: (libc)Classification of Characters. * isdigit: (libc)Classification of Characters. * iseqsig: (libc)FP Comparison Functions. * isfinite: (libc)Floating Point Classes. * isgraph: (libc)Classification of Characters. * isgreater: (libc)FP Comparison Functions. * isgreaterequal: (libc)FP Comparison Functions. * isinf: (libc)Floating Point Classes. * isinff: (libc)Floating Point Classes. * isinfl: (libc)Floating Point Classes. * isless: (libc)FP Comparison Functions. * islessequal: (libc)FP Comparison Functions. * islessgreater: (libc)FP Comparison Functions. * islower: (libc)Classification of Characters. * isnan: (libc)Floating Point Classes. * isnan: (libc)Floating Point Classes. * isnanf: (libc)Floating Point Classes. * isnanl: (libc)Floating Point Classes. * isnormal: (libc)Floating Point Classes. * isprint: (libc)Classification of Characters. * ispunct: (libc)Classification of Characters. * issignaling: (libc)Floating Point Classes. * isspace: (libc)Classification of Characters. * issubnormal: (libc)Floating Point Classes. * isunordered: (libc)FP Comparison Functions. * isupper: (libc)Classification of Characters. * iswalnum: (libc)Classification of Wide Characters. * iswalpha: (libc)Classification of Wide Characters. * iswblank: (libc)Classification of Wide Characters. * iswcntrl: (libc)Classification of Wide Characters. * iswctype: (libc)Classification of Wide Characters. * iswdigit: (libc)Classification of Wide Characters. * iswgraph: (libc)Classification of Wide Characters. * iswlower: (libc)Classification of Wide Characters. * iswprint: (libc)Classification of Wide Characters. * iswpunct: (libc)Classification of Wide Characters. * iswspace: (libc)Classification of Wide Characters. * iswupper: (libc)Classification of Wide Characters. * iswxdigit: (libc)Classification of Wide Characters. * isxdigit: (libc)Classification of Characters. * iszero: (libc)Floating Point Classes. * j0: (libc)Special Functions. * j0f: (libc)Special Functions. * j0fN: (libc)Special Functions. * j0fNx: (libc)Special Functions. * j0l: (libc)Special Functions. * j1: (libc)Special Functions. * j1f: (libc)Special Functions. * j1fN: (libc)Special Functions. * j1fNx: (libc)Special Functions. * j1l: (libc)Special Functions. * jn: (libc)Special Functions. * jnf: (libc)Special Functions. * jnfN: (libc)Special Functions. * jnfNx: (libc)Special Functions. * jnl: (libc)Special Functions. * jrand48: (libc)SVID Random. * jrand48_r: (libc)SVID Random. * kill: (libc)Signaling Another Process. * killpg: (libc)Signaling Another Process. * l64a: (libc)Encode Binary Data. * labs: (libc)Absolute Value. * lcong48: (libc)SVID Random. * lcong48_r: (libc)SVID Random. * ldexp: (libc)Normalization Functions. * ldexpf: (libc)Normalization Functions. * ldexpfN: (libc)Normalization Functions. * ldexpfNx: (libc)Normalization Functions. * ldexpl: (libc)Normalization Functions. * ldiv: (libc)Integer Division. * lfind: (libc)Array Search Function. * lgamma: (libc)Special Functions. * lgamma_r: (libc)Special Functions. * lgammaf: (libc)Special Functions. * lgammafN: (libc)Special Functions. * lgammafN_r: (libc)Special Functions. * lgammafNx: (libc)Special Functions. * lgammafNx_r: (libc)Special Functions. * lgammaf_r: (libc)Special Functions. * lgammal: (libc)Special Functions. * lgammal_r: (libc)Special Functions. * link: (libc)Hard Links. * linkat: (libc)Hard Links. * lio_listio64: (libc)Asynchronous Reads/Writes. * lio_listio: (libc)Asynchronous Reads/Writes. * listen: (libc)Listening. * llabs: (libc)Absolute Value. * lldiv: (libc)Integer Division. * llogb: (libc)Exponents and Logarithms. * llogbf: (libc)Exponents and Logarithms. * llogbfN: (libc)Exponents and Logarithms. * llogbfNx: (libc)Exponents and Logarithms. * llogbl: (libc)Exponents and Logarithms. * llrint: (libc)Rounding Functions. * llrintf: (libc)Rounding Functions. * llrintfN: (libc)Rounding Functions. * llrintfNx: (libc)Rounding Functions. * llrintl: (libc)Rounding Functions. * llround: (libc)Rounding Functions. * llroundf: (libc)Rounding Functions. * llroundfN: (libc)Rounding Functions. * llroundfNx: (libc)Rounding Functions. * llroundl: (libc)Rounding Functions. * localeconv: (libc)The Lame Way to Locale Data. * localtime: (libc)Broken-down Time. * localtime_r: (libc)Broken-down Time. * log10: (libc)Exponents and Logarithms. * log10f: (libc)Exponents and Logarithms. * log10fN: (libc)Exponents and Logarithms. * log10fNx: (libc)Exponents and Logarithms. * log10l: (libc)Exponents and Logarithms. * log10p1: (libc)Exponents and Logarithms. * log10p1f: (libc)Exponents and Logarithms. * log10p1fN: (libc)Exponents and Logarithms. * log10p1fNx: (libc)Exponents and Logarithms. * log10p1l: (libc)Exponents and Logarithms. * log1p: (libc)Exponents and Logarithms. * log1pf: (libc)Exponents and Logarithms. * log1pfN: (libc)Exponents and Logarithms. * log1pfNx: (libc)Exponents and Logarithms. * log1pl: (libc)Exponents and Logarithms. * log2: (libc)Exponents and Logarithms. * log2f: (libc)Exponents and Logarithms. * log2fN: (libc)Exponents and Logarithms. * log2fNx: (libc)Exponents and Logarithms. * log2l: (libc)Exponents and Logarithms. * log2p1: (libc)Exponents and Logarithms. * log2p1f: (libc)Exponents and Logarithms. * log2p1fN: (libc)Exponents and Logarithms. * log2p1fNx: (libc)Exponents and Logarithms. * log2p1l: (libc)Exponents and Logarithms. * log: (libc)Exponents and Logarithms. * logb: (libc)Exponents and Logarithms. * logbf: (libc)Exponents and Logarithms. * logbfN: (libc)Exponents and Logarithms. * logbfNx: (libc)Exponents and Logarithms. * logbl: (libc)Exponents and Logarithms. * logf: (libc)Exponents and Logarithms. * logfN: (libc)Exponents and Logarithms. * logfNx: (libc)Exponents and Logarithms. * login: (libc)Logging In and Out. * login_tty: (libc)Logging In and Out. * logl: (libc)Exponents and Logarithms. * logout: (libc)Logging In and Out. * logp1: (libc)Exponents and Logarithms. * logp1f: (libc)Exponents and Logarithms. * logp1fN: (libc)Exponents and Logarithms. * logp1fNx: (libc)Exponents and Logarithms. * logp1l: (libc)Exponents and Logarithms. * logwtmp: (libc)Logging In and Out. * longjmp: (libc)Non-Local Details. * lrand48: (libc)SVID Random. * lrand48_r: (libc)SVID Random. * lrint: (libc)Rounding Functions. * lrintf: (libc)Rounding Functions. * lrintfN: (libc)Rounding Functions. * lrintfNx: (libc)Rounding Functions. * lrintl: (libc)Rounding Functions. * lround: (libc)Rounding Functions. * lroundf: (libc)Rounding Functions. * lroundfN: (libc)Rounding Functions. * lroundfNx: (libc)Rounding Functions. * lroundl: (libc)Rounding Functions. * lsearch: (libc)Array Search Function. * lseek64: (libc)File Position Primitive. * lseek: (libc)File Position Primitive. * lstat64: (libc)Reading Attributes. * lstat: (libc)Reading Attributes. * lutimes: (libc)File Times. * madvise: (libc)Memory-mapped I/O. * makecontext: (libc)System V contexts. * mallinfo2: (libc)Statistics of Malloc. * malloc: (libc)Basic Allocation. * mallopt: (libc)Malloc Tunable Parameters. * mblen: (libc)Non-reentrant Character Conversion. * mbrlen: (libc)Converting a Character. * mbrtowc: (libc)Converting a Character. * mbsinit: (libc)Keeping the state. * mbsnrtowcs: (libc)Converting Strings. * mbsrtowcs: (libc)Converting Strings. * mbstowcs: (libc)Non-reentrant String Conversion. * mbtowc: (libc)Non-reentrant Character Conversion. * mcheck: (libc)Heap Consistency Checking. * memalign: (libc)Aligned Memory Blocks. * memccpy: (libc)Copying Strings and Arrays. * memchr: (libc)Search Functions. * memcmp: (libc)String/Array Comparison. * memcpy: (libc)Copying Strings and Arrays. * memfd_create: (libc)Memory-mapped I/O. * memfrob: (libc)Obfuscating Data. * memmem: (libc)Search Functions. * memmove: (libc)Copying Strings and Arrays. * mempcpy: (libc)Copying Strings and Arrays. * memrchr: (libc)Search Functions. * memset: (libc)Copying Strings and Arrays. * mkdir: (libc)Creating Directories. * mkdtemp: (libc)Temporary Files. * mkfifo: (libc)FIFO Special Files. * mknod: (libc)Making Special Files. * mkstemp: (libc)Temporary Files. * mktemp: (libc)Temporary Files. * mktime: (libc)Broken-down Time. * mlock2: (libc)Page Lock Functions. * mlock: (libc)Page Lock Functions. * mlockall: (libc)Page Lock Functions. * mmap64: (libc)Memory-mapped I/O. * mmap: (libc)Memory-mapped I/O. * modf: (libc)Rounding Functions. * modff: (libc)Rounding Functions. * modffN: (libc)Rounding Functions. * modffNx: (libc)Rounding Functions. * modfl: (libc)Rounding Functions. * mount: (libc)Mount-Unmount-Remount. * mprobe: (libc)Heap Consistency Checking. * mprotect: (libc)Memory Protection. * mrand48: (libc)SVID Random. * mrand48_r: (libc)SVID Random. * mremap: (libc)Memory-mapped I/O. * msync: (libc)Memory-mapped I/O. * mtrace: (libc)Tracing malloc. * mtx_destroy: (libc)ISO C Mutexes. * mtx_init: (libc)ISO C Mutexes. * mtx_lock: (libc)ISO C Mutexes. * mtx_timedlock: (libc)ISO C Mutexes. * mtx_trylock: (libc)ISO C Mutexes. * mtx_unlock: (libc)ISO C Mutexes. * munlock: (libc)Page Lock Functions. * munlockall: (libc)Page Lock Functions. * munmap: (libc)Memory-mapped I/O. * muntrace: (libc)Tracing malloc. * nan: (libc)FP Bit Twiddling. * nanf: (libc)FP Bit Twiddling. * nanfN: (libc)FP Bit Twiddling. * nanfNx: (libc)FP Bit Twiddling. * nanl: (libc)FP Bit Twiddling. * nanosleep: (libc)Sleeping. * nearbyint: (libc)Rounding Functions. * nearbyintf: (libc)Rounding Functions. * nearbyintfN: (libc)Rounding Functions. * nearbyintfNx: (libc)Rounding Functions. * nearbyintl: (libc)Rounding Functions. * nextafter: (libc)FP Bit Twiddling. * nextafterf: (libc)FP Bit Twiddling. * nextafterfN: (libc)FP Bit Twiddling. * nextafterfNx: (libc)FP Bit Twiddling. * nextafterl: (libc)FP Bit Twiddling. * nextdown: (libc)FP Bit Twiddling. * nextdownf: (libc)FP Bit Twiddling. * nextdownfN: (libc)FP Bit Twiddling. * nextdownfNx: (libc)FP Bit Twiddling. * nextdownl: (libc)FP Bit Twiddling. * nexttoward: (libc)FP Bit Twiddling. * nexttowardf: (libc)FP Bit Twiddling. * nexttowardl: (libc)FP Bit Twiddling. * nextup: (libc)FP Bit Twiddling. * nextupf: (libc)FP Bit Twiddling. * nextupfN: (libc)FP Bit Twiddling. * nextupfNx: (libc)FP Bit Twiddling. * nextupl: (libc)FP Bit Twiddling. * nftw64: (libc)Working with Directory Trees. * nftw: (libc)Working with Directory Trees. * ngettext: (libc)Advanced gettext functions. * nice: (libc)Traditional Scheduling Functions. * nl_langinfo: (libc)The Elegant and Fast Way. * nrand48: (libc)SVID Random. * nrand48_r: (libc)SVID Random. * ntohl: (libc)Byte Order. * ntohs: (libc)Byte Order. * ntp_adjtime: (libc)Setting and Adjusting the Time. * ntp_gettime: (libc)Setting and Adjusting the Time. * obstack_1grow: (libc)Growing Objects. * obstack_1grow_fast: (libc)Extra Fast Growing. * obstack_alignment_mask: (libc)Obstacks Data Alignment. * obstack_alloc: (libc)Allocation in an Obstack. * obstack_base: (libc)Status of an Obstack. * obstack_blank: (libc)Growing Objects. * obstack_blank_fast: (libc)Extra Fast Growing. * obstack_chunk_size: (libc)Obstack Chunks. * obstack_copy0: (libc)Allocation in an Obstack. * obstack_copy: (libc)Allocation in an Obstack. * obstack_finish: (libc)Growing Objects. * obstack_free: (libc)Freeing Obstack Objects. * obstack_grow0: (libc)Growing Objects. * obstack_grow: (libc)Growing Objects. * obstack_init: (libc)Preparing for Obstacks. * obstack_int_grow: (libc)Growing Objects. * obstack_int_grow_fast: (libc)Extra Fast Growing. * obstack_next_free: (libc)Status of an Obstack. * obstack_object_size: (libc)Growing Objects. * obstack_object_size: (libc)Status of an Obstack. * obstack_printf: (libc)Dynamic Output. * obstack_ptr_grow: (libc)Growing Objects. * obstack_ptr_grow_fast: (libc)Extra Fast Growing. * obstack_room: (libc)Extra Fast Growing. * obstack_vprintf: (libc)Variable Arguments Output. * offsetof: (libc)Structure Measurement. * on_exit: (libc)Cleanups on Exit. * open64: (libc)Opening and Closing Files. * open: (libc)Opening and Closing Files. * open_memstream: (libc)String Streams. * openat64: (libc)Opening and Closing Files. * openat: (libc)Opening and Closing Files. * opendir: (libc)Opening a Directory. * openlog: (libc)openlog. * openpty: (libc)Pseudo-Terminal Pairs. * parse_printf_format: (libc)Parsing a Template String. * pathconf: (libc)Pathconf. * pause: (libc)Using Pause. * pclose: (libc)Pipe to a Subprocess. * perror: (libc)Error Messages. * pidfd_getpid: (libc)Querying a Process. * pipe: (libc)Creating a Pipe. * pkey_alloc: (libc)Memory Protection. * pkey_free: (libc)Memory Protection. * pkey_get: (libc)Memory Protection. * pkey_mprotect: (libc)Memory Protection. * pkey_set: (libc)Memory Protection. * poll: (libc)Other Low-Level I/O APIs. * popen: (libc)Pipe to a Subprocess. * posix_fallocate64: (libc)Storage Allocation. * posix_fallocate: (libc)Storage Allocation. * posix_memalign: (libc)Aligned Memory Blocks. * posix_openpt: (libc)Allocation. * pow: (libc)Exponents and Logarithms. * powf: (libc)Exponents and Logarithms. * powfN: (libc)Exponents and Logarithms. * powfNx: (libc)Exponents and Logarithms. * powl: (libc)Exponents and Logarithms. * pread64: (libc)I/O Primitives. * pread: (libc)I/O Primitives. * preadv2: (libc)Scatter-Gather. * preadv64: (libc)Scatter-Gather. * preadv64v2: (libc)Scatter-Gather. * preadv: (libc)Scatter-Gather. * printf: (libc)Formatted Output Functions. * printf_size: (libc)Predefined Printf Handlers. * printf_size_info: (libc)Predefined Printf Handlers. * psignal: (libc)Signal Messages. * pthread_attr_getsigmask_np: (libc)Initial Thread Signal Mask. * pthread_attr_setsigmask_np: (libc)Initial Thread Signal Mask. * pthread_clockjoin_np: (libc)Waiting with Explicit Clocks. * pthread_cond_clockwait: (libc)Waiting with Explicit Clocks. * pthread_getattr_default_np: (libc)Default Thread Attributes. * pthread_getspecific: (libc)Thread-specific Data. * pthread_key_create: (libc)Thread-specific Data. * pthread_key_delete: (libc)Thread-specific Data. * pthread_rwlock_clockrdlock: (libc)Waiting with Explicit Clocks. * pthread_rwlock_clockwrlock: (libc)Waiting with Explicit Clocks. * pthread_setattr_default_np: (libc)Default Thread Attributes. * pthread_setspecific: (libc)Thread-specific Data. * pthread_timedjoin_np: (libc)Waiting with Explicit Clocks. * pthread_tryjoin_np: (libc)Waiting with Explicit Clocks. * ptsname: (libc)Allocation. * ptsname_r: (libc)Allocation. * putc: (libc)Simple Output. * putc_unlocked: (libc)Simple Output. * putchar: (libc)Simple Output. * putchar_unlocked: (libc)Simple Output. * putenv: (libc)Environment Access. * putpwent: (libc)Writing a User Entry. * puts: (libc)Simple Output. * pututline: (libc)Manipulating the Database. * pututxline: (libc)XPG Functions. * putw: (libc)Simple Output. * putwc: (libc)Simple Output. * putwc_unlocked: (libc)Simple Output. * putwchar: (libc)Simple Output. * putwchar_unlocked: (libc)Simple Output. * pwrite64: (libc)I/O Primitives. * pwrite: (libc)I/O Primitives. * pwritev2: (libc)Scatter-Gather. * pwritev64: (libc)Scatter-Gather. * pwritev64v2: (libc)Scatter-Gather. * pwritev: (libc)Scatter-Gather. * qecvt: (libc)System V Number Conversion. * qecvt_r: (libc)System V Number Conversion. * qfcvt: (libc)System V Number Conversion. * qfcvt_r: (libc)System V Number Conversion. * qgcvt: (libc)System V Number Conversion. * qsort: (libc)Array Sort Function. * raise: (libc)Signaling Yourself. * rand: (libc)ISO Random. * rand_r: (libc)ISO Random. * random: (libc)BSD Random. * random_r: (libc)BSD Random. * rawmemchr: (libc)Search Functions. * read: (libc)I/O Primitives. * readdir64: (libc)Reading/Closing Directory. * readdir64_r: (libc)Reading/Closing Directory. * readdir: (libc)Reading/Closing Directory. * readdir_r: (libc)Reading/Closing Directory. * readlink: (libc)Symbolic Links. * readv: (libc)Scatter-Gather. * realloc: (libc)Changing Block Size. * reallocarray: (libc)Changing Block Size. * realpath: (libc)Symbolic Links. * recv: (libc)Receiving Data. * recvfrom: (libc)Receiving Datagrams. * recvmsg: (libc)Other Socket APIs. * regcomp: (libc)POSIX Regexp Compilation. * regerror: (libc)Regexp Cleanup. * regexec: (libc)Matching POSIX Regexps. * regfree: (libc)Regexp Cleanup. * register_printf_function: (libc)Registering New Conversions. * remainder: (libc)Remainder Functions. * remainderf: (libc)Remainder Functions. * remainderfN: (libc)Remainder Functions. * remainderfNx: (libc)Remainder Functions. * remainderl: (libc)Remainder Functions. * remove: (libc)Deleting Files. * rename: (libc)Renaming Files. * rewind: (libc)File Positioning. * rewinddir: (libc)Random Access Directory. * rindex: (libc)Search Functions. * rint: (libc)Rounding Functions. * rintf: (libc)Rounding Functions. * rintfN: (libc)Rounding Functions. * rintfNx: (libc)Rounding Functions. * rintl: (libc)Rounding Functions. * rmdir: (libc)Deleting Files. * round: (libc)Rounding Functions. * roundeven: (libc)Rounding Functions. * roundevenf: (libc)Rounding Functions. * roundevenfN: (libc)Rounding Functions. * roundevenfNx: (libc)Rounding Functions. * roundevenl: (libc)Rounding Functions. * roundf: (libc)Rounding Functions. * roundfN: (libc)Rounding Functions. * roundfNx: (libc)Rounding Functions. * roundl: (libc)Rounding Functions. * rpmatch: (libc)Yes-or-No Questions. * sbrk: (libc)Resizing the Data Segment. * scalb: (libc)Normalization Functions. * scalbf: (libc)Normalization Functions. * scalbl: (libc)Normalization Functions. * scalbln: (libc)Normalization Functions. * scalblnf: (libc)Normalization Functions. * scalblnfN: (libc)Normalization Functions. * scalblnfNx: (libc)Normalization Functions. * scalblnl: (libc)Normalization Functions. * scalbn: (libc)Normalization Functions. * scalbnf: (libc)Normalization Functions. * scalbnfN: (libc)Normalization Functions. * scalbnfNx: (libc)Normalization Functions. * scalbnl: (libc)Normalization Functions. * scandir64: (libc)Scanning Directory Content. * scandir: (libc)Scanning Directory Content. * scanf: (libc)Formatted Input Functions. * sched_get_priority_max: (libc)Basic Scheduling Functions. * sched_get_priority_min: (libc)Basic Scheduling Functions. * sched_getaddr: (libc)Extensible Scheduling. * sched_getaffinity: (libc)CPU Affinity. * sched_getparam: (libc)Basic Scheduling Functions. * sched_getscheduler: (libc)Basic Scheduling Functions. * sched_rr_get_interval: (libc)Basic Scheduling Functions. * sched_setaddr: (libc)Extensible Scheduling. * sched_setaffinity: (libc)CPU Affinity. * sched_setparam: (libc)Basic Scheduling Functions. * sched_setscheduler: (libc)Basic Scheduling Functions. * sched_yield: (libc)Basic Scheduling Functions. * secure_getenv: (libc)Environment Access. * seed48: (libc)SVID Random. * seed48_r: (libc)SVID Random. * seekdir: (libc)Random Access Directory. * select: (libc)Waiting for I/O. * sem_clockwait: (libc)Waiting with Explicit Clocks. * sem_close: (libc)Semaphores. * sem_destroy: (libc)Semaphores. * sem_getvalue: (libc)Semaphores. * sem_init: (libc)Semaphores. * sem_open: (libc)Semaphores. * sem_post: (libc)Semaphores. * sem_timedwait: (libc)Semaphores. * sem_trywait: (libc)Semaphores. * sem_unlink: (libc)Semaphores. * sem_wait: (libc)Semaphores. * semctl: (libc)Semaphores. * semget: (libc)Semaphores. * semop: (libc)Semaphores. * semtimedop: (libc)Semaphores. * send: (libc)Sending Data. * sendmsg: (libc)Other Socket APIs. * sendto: (libc)Sending Datagrams. * setbuf: (libc)Controlling Buffering. * setbuffer: (libc)Controlling Buffering. * setcontext: (libc)System V contexts. * setdomainname: (libc)Host Identification. * setegid: (libc)Setting Groups. * setenv: (libc)Environment Access. * seteuid: (libc)Setting User ID. * setfsent: (libc)fstab. * setgid: (libc)Setting Groups. * setgrent: (libc)Scanning All Groups. * setgroups: (libc)Setting Groups. * sethostent: (libc)Host Names. * sethostid: (libc)Host Identification. * sethostname: (libc)Host Identification. * setitimer: (libc)Setting an Alarm. * setjmp: (libc)Non-Local Details. * setlinebuf: (libc)Controlling Buffering. * setlocale: (libc)Setting the Locale. * setlogmask: (libc)setlogmask. * setmntent: (libc)mtab. * setnetent: (libc)Networks Database. * setnetgrent: (libc)Lookup Netgroup. * setpayload: (libc)FP Bit Twiddling. * setpayloadf: (libc)FP Bit Twiddling. * setpayloadfN: (libc)FP Bit Twiddling. * setpayloadfNx: (libc)FP Bit Twiddling. * setpayloadl: (libc)FP Bit Twiddling. * setpayloadsig: (libc)FP Bit Twiddling. * setpayloadsigf: (libc)FP Bit Twiddling. * setpayloadsigfN: (libc)FP Bit Twiddling. * setpayloadsigfNx: (libc)FP Bit Twiddling. * setpayloadsigl: (libc)FP Bit Twiddling. * setpgid: (libc)Process Group Functions. * setpgrp: (libc)Process Group Functions. * setpriority: (libc)Traditional Scheduling Functions. * setprotoent: (libc)Protocols Database. * setpwent: (libc)Scanning All Users. * setregid: (libc)Setting Groups. * setreuid: (libc)Setting User ID. * setrlimit64: (libc)Limits on Resources. * setrlimit: (libc)Limits on Resources. * setservent: (libc)Services Database. * setsid: (libc)Process Group Functions. * setsockopt: (libc)Socket Option Functions. * setstate: (libc)BSD Random. * setstate_r: (libc)BSD Random. * settimeofday: (libc)Setting and Adjusting the Time. * setuid: (libc)Setting User ID. * setutent: (libc)Manipulating the Database. * setutxent: (libc)XPG Functions. * setvbuf: (libc)Controlling Buffering. * shm_open: (libc)Memory-mapped I/O. * shm_unlink: (libc)Memory-mapped I/O. * shutdown: (libc)Closing a Socket. * sigabbrev_np: (libc)Signal Messages. * sigaction: (libc)Advanced Signal Handling. * sigaddset: (libc)Signal Sets. * sigaltstack: (libc)Signal Stack. * sigblock: (libc)BSD Signal Handling. * sigdelset: (libc)Signal Sets. * sigdescr_np: (libc)Signal Messages. * sigemptyset: (libc)Signal Sets. * sigfillset: (libc)Signal Sets. * siginterrupt: (libc)BSD Signal Handling. * sigismember: (libc)Signal Sets. * siglongjmp: (libc)Non-Local Exits and Signals. * sigmask: (libc)BSD Signal Handling. * signal: (libc)Basic Signal Handling. * signbit: (libc)FP Bit Twiddling. * significand: (libc)Normalization Functions. * significandf: (libc)Normalization Functions. * significandl: (libc)Normalization Functions. * sigpause: (libc)BSD Signal Handling. * sigpending: (libc)Checking for Pending Signals. * sigprocmask: (libc)Process Signal Mask. * sigsetjmp: (libc)Non-Local Exits and Signals. * sigsetmask: (libc)BSD Signal Handling. * sigstack: (libc)Signal Stack. * sigsuspend: (libc)Sigsuspend. * sin: (libc)Trig Functions. * sincos: (libc)Trig Functions. * sincosf: (libc)Trig Functions. * sincosfN: (libc)Trig Functions. * sincosfNx: (libc)Trig Functions. * sincosl: (libc)Trig Functions. * sinf: (libc)Trig Functions. * sinfN: (libc)Trig Functions. * sinfNx: (libc)Trig Functions. * sinh: (libc)Hyperbolic Functions. * sinhf: (libc)Hyperbolic Functions. * sinhfN: (libc)Hyperbolic Functions. * sinhfNx: (libc)Hyperbolic Functions. * sinhl: (libc)Hyperbolic Functions. * sinl: (libc)Trig Functions. * sinpi: (libc)Trig Functions. * sinpif: (libc)Trig Functions. * sinpifN: (libc)Trig Functions. * sinpifNx: (libc)Trig Functions. * sinpil: (libc)Trig Functions. * sleep: (libc)Sleeping. * snprintf: (libc)Formatted Output Functions. * socket: (libc)Creating a Socket. * socketpair: (libc)Socket Pairs. * sprintf: (libc)Formatted Output Functions. * sqrt: (libc)Exponents and Logarithms. * sqrtf: (libc)Exponents and Logarithms. * sqrtfN: (libc)Exponents and Logarithms. * sqrtfNx: (libc)Exponents and Logarithms. * sqrtl: (libc)Exponents and Logarithms. * srand48: (libc)SVID Random. * srand48_r: (libc)SVID Random. * srand: (libc)ISO Random. * srandom: (libc)BSD Random. * srandom_r: (libc)BSD Random. * sscanf: (libc)Formatted Input Functions. * ssignal: (libc)Basic Signal Handling. * stat64: (libc)Reading Attributes. * stat: (libc)Reading Attributes. * stdc_bit_ceil_uc: (libc)Bit Manipulation. * stdc_bit_ceil_ui: (libc)Bit Manipulation. * stdc_bit_ceil_ul: (libc)Bit Manipulation. * stdc_bit_ceil_ull: (libc)Bit Manipulation. * stdc_bit_ceil_us: (libc)Bit Manipulation. * stdc_bit_floor_uc: (libc)Bit Manipulation. * stdc_bit_floor_ui: (libc)Bit Manipulation. * stdc_bit_floor_ul: (libc)Bit Manipulation. * stdc_bit_floor_ull: (libc)Bit Manipulation. * stdc_bit_floor_us: (libc)Bit Manipulation. * stdc_bit_width_uc: (libc)Bit Manipulation. * stdc_bit_width_ui: (libc)Bit Manipulation. * stdc_bit_width_ul: (libc)Bit Manipulation. * stdc_bit_width_ull: (libc)Bit Manipulation. * stdc_bit_width_us: (libc)Bit Manipulation. * stdc_count_ones_uc: (libc)Bit Manipulation. * stdc_count_ones_ui: (libc)Bit Manipulation. * stdc_count_ones_ul: (libc)Bit Manipulation. * stdc_count_ones_ull: (libc)Bit Manipulation. * stdc_count_ones_us: (libc)Bit Manipulation. * stdc_count_zeros_uc: (libc)Bit Manipulation. * stdc_count_zeros_ui: (libc)Bit Manipulation. * stdc_count_zeros_ul: (libc)Bit Manipulation. * stdc_count_zeros_ull: (libc)Bit Manipulation. * stdc_count_zeros_us: (libc)Bit Manipulation. * stdc_first_leading_one_uc: (libc)Bit Manipulation. * stdc_first_leading_one_ui: (libc)Bit Manipulation. * stdc_first_leading_one_ul: (libc)Bit Manipulation. * stdc_first_leading_one_ull: (libc)Bit Manipulation. * stdc_first_leading_one_us: (libc)Bit Manipulation. * stdc_first_leading_zero_uc: (libc)Bit Manipulation. * stdc_first_leading_zero_ui: (libc)Bit Manipulation. * stdc_first_leading_zero_ul: (libc)Bit Manipulation. * stdc_first_leading_zero_ull: (libc)Bit Manipulation. * stdc_first_leading_zero_us: (libc)Bit Manipulation. * stdc_first_trailing_one_uc: (libc)Bit Manipulation. * stdc_first_trailing_one_ui: (libc)Bit Manipulation. * stdc_first_trailing_one_ul: (libc)Bit Manipulation. * stdc_first_trailing_one_ull: (libc)Bit Manipulation. * stdc_first_trailing_one_us: (libc)Bit Manipulation. * stdc_first_trailing_zero_uc: (libc)Bit Manipulation. * stdc_first_trailing_zero_ui: (libc)Bit Manipulation. * stdc_first_trailing_zero_ul: (libc)Bit Manipulation. * stdc_first_trailing_zero_ull: (libc)Bit Manipulation. * stdc_first_trailing_zero_us: (libc)Bit Manipulation. * stdc_has_single_bit_uc: (libc)Bit Manipulation. * stdc_has_single_bit_ui: (libc)Bit Manipulation. * stdc_has_single_bit_ul: (libc)Bit Manipulation. * stdc_has_single_bit_ull: (libc)Bit Manipulation. * stdc_has_single_bit_us: (libc)Bit Manipulation. * stdc_leading_ones_uc: (libc)Bit Manipulation. * stdc_leading_ones_ui: (libc)Bit Manipulation. * stdc_leading_ones_ul: (libc)Bit Manipulation. * stdc_leading_ones_ull: (libc)Bit Manipulation. * stdc_leading_ones_us: (libc)Bit Manipulation. * stdc_leading_zeros_uc: (libc)Bit Manipulation. * stdc_leading_zeros_ui: (libc)Bit Manipulation. * stdc_leading_zeros_ul: (libc)Bit Manipulation. * stdc_leading_zeros_ull: (libc)Bit Manipulation. * stdc_leading_zeros_us: (libc)Bit Manipulation. * stdc_trailing_ones_uc: (libc)Bit Manipulation. * stdc_trailing_ones_ui: (libc)Bit Manipulation. * stdc_trailing_ones_ul: (libc)Bit Manipulation. * stdc_trailing_ones_ull: (libc)Bit Manipulation. * stdc_trailing_ones_us: (libc)Bit Manipulation. * stdc_trailing_zeros_uc: (libc)Bit Manipulation. * stdc_trailing_zeros_ui: (libc)Bit Manipulation. * stdc_trailing_zeros_ul: (libc)Bit Manipulation. * stdc_trailing_zeros_ull: (libc)Bit Manipulation. * stdc_trailing_zeros_us: (libc)Bit Manipulation. * stime: (libc)Setting and Adjusting the Time. * stpcpy: (libc)Copying Strings and Arrays. * stpncpy: (libc)Truncating Strings. * strcasecmp: (libc)String/Array Comparison. * strcasestr: (libc)Search Functions. * strcat: (libc)Concatenating Strings. * strchr: (libc)Search Functions. * strchrnul: (libc)Search Functions. * strcmp: (libc)String/Array Comparison. * strcoll: (libc)Collation Functions. * strcpy: (libc)Copying Strings and Arrays. * strcspn: (libc)Search Functions. * strdup: (libc)Copying Strings and Arrays. * strdupa: (libc)Copying Strings and Arrays. * strerror: (libc)Error Messages. * strerror_l: (libc)Error Messages. * strerror_r: (libc)Error Messages. * strerror_r: (libc)Error Messages. * strerrordesc_np: (libc)Error Messages. * strerrorname_np: (libc)Error Messages. * strfmon: (libc)Formatting Numbers. * strfromd: (libc)Printing of Floats. * strfromf: (libc)Printing of Floats. * strfromfN: (libc)Printing of Floats. * strfromfNx: (libc)Printing of Floats. * strfroml: (libc)Printing of Floats. * strfry: (libc)Shuffling Bytes. * strftime: (libc)Formatting Calendar Time. * strftime_l: (libc)Formatting Calendar Time. * strlcat: (libc)Truncating Strings. * strlcpy: (libc)Truncating Strings. * strlen: (libc)String Length. * strncasecmp: (libc)String/Array Comparison. * strncat: (libc)Truncating Strings. * strncmp: (libc)String/Array Comparison. * strncpy: (libc)Truncating Strings. * strndup: (libc)Truncating Strings. * strndupa: (libc)Truncating Strings. * strnlen: (libc)String Length. * strpbrk: (libc)Search Functions. * strptime: (libc)Low-Level Time String Parsing. * strrchr: (libc)Search Functions. * strsep: (libc)Finding Tokens in a String. * strsignal: (libc)Signal Messages. * strspn: (libc)Search Functions. * strstr: (libc)Search Functions. * strtod: (libc)Parsing of Floats. * strtof: (libc)Parsing of Floats. * strtofN: (libc)Parsing of Floats. * strtofNx: (libc)Parsing of Floats. * strtoimax: (libc)Parsing of Integers. * strtok: (libc)Finding Tokens in a String. * strtok_r: (libc)Finding Tokens in a String. * strtol: (libc)Parsing of Integers. * strtold: (libc)Parsing of Floats. * strtoll: (libc)Parsing of Integers. * strtoq: (libc)Parsing of Integers. * strtoul: (libc)Parsing of Integers. * strtoull: (libc)Parsing of Integers. * strtoumax: (libc)Parsing of Integers. * strtouq: (libc)Parsing of Integers. * strverscmp: (libc)String/Array Comparison. * strxfrm: (libc)Collation Functions. * stty: (libc)BSD Terminal Modes. * swapcontext: (libc)System V contexts. * swprintf: (libc)Formatted Output Functions. * swscanf: (libc)Formatted Input Functions. * symlink: (libc)Symbolic Links. * sync: (libc)Synchronizing I/O. * syscall: (libc)System Calls. * sysconf: (libc)Sysconf Definition. * syslog: (libc)syslog; vsyslog. * system: (libc)Running a Command. * sysv_signal: (libc)Basic Signal Handling. * tan: (libc)Trig Functions. * tanf: (libc)Trig Functions. * tanfN: (libc)Trig Functions. * tanfNx: (libc)Trig Functions. * tanh: (libc)Hyperbolic Functions. * tanhf: (libc)Hyperbolic Functions. * tanhfN: (libc)Hyperbolic Functions. * tanhfNx: (libc)Hyperbolic Functions. * tanhl: (libc)Hyperbolic Functions. * tanl: (libc)Trig Functions. * tanpi: (libc)Trig Functions. * tanpif: (libc)Trig Functions. * tanpifN: (libc)Trig Functions. * tanpifNx: (libc)Trig Functions. * tanpil: (libc)Trig Functions. * tcdrain: (libc)Line Control. * tcflow: (libc)Line Control. * tcflush: (libc)Line Control. * tcgetattr: (libc)Mode Functions. * tcgetpgrp: (libc)Terminal Access Functions. * tcgetsid: (libc)Terminal Access Functions. * tcsendbreak: (libc)Line Control. * tcsetattr: (libc)Mode Functions. * tcsetpgrp: (libc)Terminal Access Functions. * tdelete: (libc)Tree Search Function. * tdestroy: (libc)Tree Search Function. * telldir: (libc)Random Access Directory. * tempnam: (libc)Temporary Files. * textdomain: (libc)Locating gettext catalog. * tfind: (libc)Tree Search Function. * tgamma: (libc)Special Functions. * tgammaf: (libc)Special Functions. * tgammafN: (libc)Special Functions. * tgammafNx: (libc)Special Functions. * tgammal: (libc)Special Functions. * tgkill: (libc)Signaling Another Process. * thrd_create: (libc)ISO C Thread Management. * thrd_current: (libc)ISO C Thread Management. * thrd_detach: (libc)ISO C Thread Management. * thrd_equal: (libc)ISO C Thread Management. * thrd_exit: (libc)ISO C Thread Management. * thrd_join: (libc)ISO C Thread Management. * thrd_sleep: (libc)ISO C Thread Management. * thrd_yield: (libc)ISO C Thread Management. * time: (libc)Getting the Time. * timegm: (libc)Broken-down Time. * timelocal: (libc)Broken-down Time. * times: (libc)Processor Time. * timespec_get: (libc)Getting the Time. * timespec_getres: (libc)Getting the Time. * tmpfile64: (libc)Temporary Files. * tmpfile: (libc)Temporary Files. * tmpnam: (libc)Temporary Files. * tmpnam_r: (libc)Temporary Files. * toascii: (libc)Case Conversion. * tolower: (libc)Case Conversion. * totalorder: (libc)FP Comparison Functions. * totalorderf: (libc)FP Comparison Functions. * totalorderfN: (libc)FP Comparison Functions. * totalorderfNx: (libc)FP Comparison Functions. * totalorderl: (libc)FP Comparison Functions. * totalordermag: (libc)FP Comparison Functions. * totalordermagf: (libc)FP Comparison Functions. * totalordermagfN: (libc)FP Comparison Functions. * totalordermagfNx: (libc)FP Comparison Functions. * totalordermagl: (libc)FP Comparison Functions. * toupper: (libc)Case Conversion. * towctrans: (libc)Wide Character Case Conversion. * towlower: (libc)Wide Character Case Conversion. * towupper: (libc)Wide Character Case Conversion. * trunc: (libc)Rounding Functions. * truncate64: (libc)File Size. * truncate: (libc)File Size. * truncf: (libc)Rounding Functions. * truncfN: (libc)Rounding Functions. * truncfNx: (libc)Rounding Functions. * truncl: (libc)Rounding Functions. * tsearch: (libc)Tree Search Function. * tss_create: (libc)ISO C Thread-local Storage. * tss_delete: (libc)ISO C Thread-local Storage. * tss_get: (libc)ISO C Thread-local Storage. * tss_set: (libc)ISO C Thread-local Storage. * ttyname: (libc)Is It a Terminal. * ttyname_r: (libc)Is It a Terminal. * twalk: (libc)Tree Search Function. * twalk_r: (libc)Tree Search Function. * tzset: (libc)Time Zone State. * ufromfp: (libc)Rounding Functions. * ufromfpf: (libc)Rounding Functions. * ufromfpfN: (libc)Rounding Functions. * ufromfpfNx: (libc)Rounding Functions. * ufromfpl: (libc)Rounding Functions. * ufromfpx: (libc)Rounding Functions. * ufromfpxf: (libc)Rounding Functions. * ufromfpxfN: (libc)Rounding Functions. * ufromfpxfNx: (libc)Rounding Functions. * ufromfpxl: (libc)Rounding Functions. * ulimit: (libc)Limits on Resources. * umask: (libc)Setting Permissions. * umount2: (libc)Mount-Unmount-Remount. * umount: (libc)Mount-Unmount-Remount. * uname: (libc)Platform Type. * ungetc: (libc)How Unread. * ungetwc: (libc)How Unread. * unlink: (libc)Deleting Files. * unlockpt: (libc)Allocation. * unsetenv: (libc)Environment Access. * updwtmp: (libc)Manipulating the Database. * utime: (libc)File Times. * utimes: (libc)File Times. * utmpname: (libc)Manipulating the Database. * utmpxname: (libc)XPG Functions. * va_arg: (libc)Argument Macros. * va_copy: (libc)Argument Macros. * va_end: (libc)Argument Macros. * va_start: (libc)Argument Macros. * valloc: (libc)Aligned Memory Blocks. * vasprintf: (libc)Variable Arguments Output. * vdprintf: (libc)Variable Arguments Output. * verr: (libc)Error Messages. * verrx: (libc)Error Messages. * versionsort64: (libc)Scanning Directory Content. * versionsort: (libc)Scanning Directory Content. * vfork: (libc)Creating a Process. * vfprintf: (libc)Variable Arguments Output. * vfscanf: (libc)Variable Arguments Input. * vfwprintf: (libc)Variable Arguments Output. * vfwscanf: (libc)Variable Arguments Input. * vlimit: (libc)Limits on Resources. * vprintf: (libc)Variable Arguments Output. * vscanf: (libc)Variable Arguments Input. * vsnprintf: (libc)Variable Arguments Output. * vsprintf: (libc)Variable Arguments Output. * vsscanf: (libc)Variable Arguments Input. * vswprintf: (libc)Variable Arguments Output. * vswscanf: (libc)Variable Arguments Input. * vsyslog: (libc)syslog; vsyslog. * vwarn: (libc)Error Messages. * vwarnx: (libc)Error Messages. * vwprintf: (libc)Variable Arguments Output. * vwscanf: (libc)Variable Arguments Input. * wait3: (libc)BSD Wait Functions. * wait4: (libc)Process Completion. * wait: (libc)Process Completion. * waitpid: (libc)Process Completion. * warn: (libc)Error Messages. * warnx: (libc)Error Messages. * wcpcpy: (libc)Copying Strings and Arrays. * wcpncpy: (libc)Truncating Strings. * wcrtomb: (libc)Converting a Character. * wcscasecmp: (libc)String/Array Comparison. * wcscat: (libc)Concatenating Strings. * wcschr: (libc)Search Functions. * wcschrnul: (libc)Search Functions. * wcscmp: (libc)String/Array Comparison. * wcscoll: (libc)Collation Functions. * wcscpy: (libc)Copying Strings and Arrays. * wcscspn: (libc)Search Functions. * wcsdup: (libc)Copying Strings and Arrays. * wcsftime: (libc)Formatting Calendar Time. * wcslcat: (libc)Truncating Strings. * wcslcpy: (libc)Truncating Strings. * wcslen: (libc)String Length. * wcsncasecmp: (libc)String/Array Comparison. * wcsncat: (libc)Truncating Strings. * wcsncmp: (libc)String/Array Comparison. * wcsncpy: (libc)Truncating Strings. * wcsnlen: (libc)String Length. * wcsnrtombs: (libc)Converting Strings. * wcspbrk: (libc)Search Functions. * wcsrchr: (libc)Search Functions. * wcsrtombs: (libc)Converting Strings. * wcsspn: (libc)Search Functions. * wcsstr: (libc)Search Functions. * wcstod: (libc)Parsing of Floats. * wcstof: (libc)Parsing of Floats. * wcstofN: (libc)Parsing of Floats. * wcstofNx: (libc)Parsing of Floats. * wcstoimax: (libc)Parsing of Integers. * wcstok: (libc)Finding Tokens in a String. * wcstol: (libc)Parsing of Integers. * wcstold: (libc)Parsing of Floats. * wcstoll: (libc)Parsing of Integers. * wcstombs: (libc)Non-reentrant String Conversion. * wcstoq: (libc)Parsing of Integers. * wcstoul: (libc)Parsing of Integers. * wcstoull: (libc)Parsing of Integers. * wcstoumax: (libc)Parsing of Integers. * wcstouq: (libc)Parsing of Integers. * wcswcs: (libc)Search Functions. * wcsxfrm: (libc)Collation Functions. * wctob: (libc)Converting a Character. * wctomb: (libc)Non-reentrant Character Conversion. * wctrans: (libc)Wide Character Case Conversion. * wctype: (libc)Classification of Wide Characters. * wmemchr: (libc)Search Functions. * wmemcmp: (libc)String/Array Comparison. * wmemcpy: (libc)Copying Strings and Arrays. * wmemmove: (libc)Copying Strings and Arrays. * wmempcpy: (libc)Copying Strings and Arrays. * wmemset: (libc)Copying Strings and Arrays. * wordexp: (libc)Calling Wordexp. * wordfree: (libc)Calling Wordexp. * wprintf: (libc)Formatted Output Functions. * write: (libc)I/O Primitives. * writev: (libc)Scatter-Gather. * wscanf: (libc)Formatted Input Functions. * y0: (libc)Special Functions. * y0f: (libc)Special Functions. * y0fN: (libc)Special Functions. * y0fNx: (libc)Special Functions. * y0l: (libc)Special Functions. * y1: (libc)Special Functions. * y1f: (libc)Special Functions. * y1fN: (libc)Special Functions. * y1fNx: (libc)Special Functions. * y1l: (libc)Special Functions. * yn: (libc)Special Functions. * ynf: (libc)Special Functions. * ynfN: (libc)Special Functions. * ynfNx: (libc)Special Functions. * ynl: (libc)Special Functions. END-INFO-DIR-ENTRY  File: libc.info, Node: Internet Address Formats, Next: Host Addresses, Up: Internet Namespace 16.6.1 Internet Socket Address Formats -------------------------------------- In the Internet namespace, for both IPv4 (‘AF_INET’) and IPv6 (‘AF_INET6’), a socket address consists of a host address and a port on that host. In addition, the protocol you choose serves effectively as a part of the address because local port numbers are meaningful only within a particular protocol. The data types for representing socket addresses in the Internet namespace are defined in the header file ‘netinet/in.h’. -- Data Type: struct sockaddr_in This is the data type used to represent socket addresses in the Internet namespace. It has the following members: ‘sa_family_t sin_family’ This identifies the address family or format of the socket address. You should store the value ‘AF_INET’ in this member. The address family is stored in host byte order. *Note Socket Addresses::. ‘struct in_addr sin_addr’ This is the IPv4 address. *Note Host Addresses::, and *note Host Names::, for how to get a value to store here. The IPv4 address is stored in network byte order. ‘unsigned short int sin_port’ This is the port number. *Note Ports::. The port number is stored in network byte order. When you call ‘bind’ or ‘getsockname’, you should specify ‘sizeof (struct sockaddr_in)’ as the LENGTH parameter if you are using an IPv4 Internet namespace socket address. -- Data Type: struct sockaddr_in6 This is the data type used to represent socket addresses in the IPv6 namespace. It has the following members: ‘sa_family_t sin6_family’ This identifies the address family or format of the socket address. You should store the value of ‘AF_INET6’ in this member. *Note Socket Addresses::. The address family is stored in host byte order. ‘struct in6_addr sin6_addr’ This is the IPv6 address of the host machine. *Note Host Addresses::, and *note Host Names::, for how to get a value to store here. The address is stored in network byte order. ‘uint32_t sin6_flowinfo’ This combines the IPv6 traffic class and flow label values, as found in the IPv6 header. This field is stored in network byte order. Only the 28 lower bits (of the number in network byte order) are used; the remaining bits must be zero. The lower 20 bits are the flow label, and bits 20 to 27 are the the traffic class. Typically, this field is zero. ‘uint32_t sin6_scope_id’ For link-local addresses, this identifies the interface on which this address is valid. The scope ID is stored in host byte order. Typically, this field is zero. ‘uint16_t sin6_port’ This is the port number. *Note Ports::. The port number is stored in network byte order.  File: libc.info, Node: Host Addresses, Next: Ports, Prev: Internet Address Formats, Up: Internet Namespace 16.6.2 Host Addresses --------------------- Each computer on the Internet has one or more “Internet addresses”, numbers which identify that computer among all those on the Internet. Users typically write IPv4 numeric host addresses as sequences of four numbers, separated by periods, as in ‘128.52.46.32’, and IPv6 numeric host addresses as sequences of up to eight numbers separated by colons, as in ‘5f03:1200:836f:c100::1’. Each computer also has one or more “host names”, which are strings of words separated by periods, as in ‘www.gnu.org’. Programs that let the user specify a host typically accept both numeric addresses and host names. To open a connection a program needs a numeric address, and so must convert a host name to the numeric address it stands for. * Menu: * Abstract Host Addresses:: What a host number consists of. * Data type: Host Address Data Type. Data type for a host number. * Functions: Host Address Functions. Functions to operate on them. * Names: Host Names. Translating host names to host numbers.  File: libc.info, Node: Abstract Host Addresses, Next: Host Address Data Type, Up: Host Addresses 16.6.2.1 Internet Host Addresses ................................ Each computer on the Internet has one or more Internet addresses, numbers which identify that computer among all those on the Internet. An IPv4 Internet host address is a number containing four bytes of data. Historically these are divided into two parts, a “network number” and a “local network address number” within that network. In the mid-1990s classless addresses were introduced which changed this behavior. Since some functions implicitly expect the old definitions, we first describe the class-based network and will then describe classless addresses. IPv6 uses only classless addresses and therefore the following paragraphs don't apply. The class-based IPv4 network number consists of the first one, two or three bytes; the rest of the bytes are the local address. IPv4 network numbers are registered with the Network Information Center (NIC), and are divided into three classes--A, B and C. The local network address numbers of individual machines are registered with the administrator of the particular network. Class A networks have single-byte numbers in the range 0 to 127. There are only a small number of Class A networks, but they can each support a very large number of hosts. Medium-sized Class B networks have two-byte network numbers, with the first byte in the range 128 to 191. Class C networks are the smallest; they have three-byte network numbers, with the first byte in the range 192-255. Thus, the first 1, 2, or 3 bytes of an Internet address specify a network. The remaining bytes of the Internet address specify the address within that network. The Class A network 0 is reserved for broadcast to all networks. In addition, the host number 0 within each network is reserved for broadcast to all hosts in that network. These uses are obsolete now but for compatibility reasons you shouldn't use network 0 and host number 0. The Class A network 127 is reserved for loopback; you can always use the Internet address ‘127.0.0.1’ to refer to the host machine. Since a single machine can be a member of multiple networks, it can have multiple Internet host addresses. However, there is never supposed to be more than one machine with the same host address. There are four forms of the “standard numbers-and-dots notation” for Internet addresses: ‘A.B.C.D’ This specifies all four bytes of the address individually and is the commonly used representation. ‘A.B.C’ The last part of the address, C, is interpreted as a 2-byte quantity. This is useful for specifying host addresses in a Class B network with network address number ‘A.B’. ‘A.B’ The last part of the address, B, is interpreted as a 3-byte quantity. This is useful for specifying host addresses in a Class A network with network address number A. ‘A’ If only one part is given, this corresponds directly to the host address number. Within each part of the address, the usual C conventions for specifying the radix apply. In other words, a leading ‘0x’ or ‘0X’ implies hexadecimal radix; a leading ‘0’ implies octal; and otherwise decimal radix is assumed. Classless Addresses ................... IPv4 addresses (and IPv6 addresses also) are now considered classless; the distinction between classes A, B and C can be ignored. Instead an IPv4 host address consists of a 32-bit address and a 32-bit mask. The mask contains set bits for the network part and cleared bits for the host part. The network part is contiguous from the left, with the remaining bits representing the host. As a consequence, the netmask can simply be specified as the number of set bits. Classes A, B and C are just special cases of this general rule. For example, class A addresses have a netmask of ‘255.0.0.0’ or a prefix length of 8. Classless IPv4 network addresses are written in numbers-and-dots notation with the prefix length appended and a slash as separator. For example the class A network 10 is written as ‘10.0.0.0/8’. IPv6 Addresses .............. IPv6 addresses contain 128 bits (IPv4 has 32 bits) of data. A host address is usually written as eight 16-bit hexadecimal numbers that are separated by colons. Two colons are used to abbreviate strings of consecutive zeros. For example, the IPv6 loopback address ‘0:0:0:0:0:0:0:1’ can just be written as ‘::1’.  File: libc.info, Node: Host Address Data Type, Next: Host Address Functions, Prev: Abstract Host Addresses, Up: Host Addresses 16.6.2.2 Host Address Data Type ............................... IPv4 Internet host addresses are represented in some contexts as integers (type ‘uint32_t’). In other contexts, the integer is packaged inside a structure of type ‘struct in_addr’. It would be better if the usage were made consistent, but it is not hard to extract the integer from the structure or put the integer into a structure. You will find older code that uses ‘unsigned long int’ for IPv4 Internet host addresses instead of ‘uint32_t’ or ‘struct in_addr’. Historically ‘unsigned long int’ was a 32-bit number but with 64-bit machines this has changed. Using ‘unsigned long int’ might break the code if it is used on machines where this type doesn't have 32 bits. ‘uint32_t’ is specified by Unix98 and guaranteed to have 32 bits. IPv6 Internet host addresses have 128 bits and are packaged inside a structure of type ‘struct in6_addr’. The following basic definitions for Internet addresses are declared in the header file ‘netinet/in.h’: -- Data Type: struct in_addr This data type is used in certain contexts to contain an IPv4 Internet host address. It has just one field, named ‘s_addr’, which records the host address number as an ‘uint32_t’. -- Macro: uint32_t INADDR_LOOPBACK You can use this constant to stand for "the address of this machine," instead of finding its actual address. It is the IPv4 Internet address ‘127.0.0.1’, which is usually called ‘localhost’. This special constant saves you the trouble of looking up the address of your own machine. Also, the system usually implements ‘INADDR_LOOPBACK’ specially, avoiding any network traffic for the case of one machine talking to itself. -- Macro: uint32_t INADDR_ANY You can use this constant to stand for "any incoming address" when binding to an address. *Note Setting Address::. This is the usual address to give in the ‘sin_addr’ member of ‘struct sockaddr_in’ when you want to accept Internet connections. -- Macro: uint32_t INADDR_BROADCAST This constant is the address you use to send a broadcast message. -- Macro: uint32_t INADDR_NONE This constant is returned by some functions to indicate an error. -- Data Type: struct in6_addr This data type is used to store an IPv6 address. It stores 128 bits of data, which can be accessed (via a union) in a variety of ways. -- Constant: struct in6_addr in6addr_loopback This constant is the IPv6 address ‘::1’, the loopback address. See above for a description of what this means. The macro ‘IN6ADDR_LOOPBACK_INIT’ is provided to allow you to initialize your own variables to this value. -- Constant: struct in6_addr in6addr_any This constant is the IPv6 address ‘::’, the unspecified address. See above for a description of what this means. The macro ‘IN6ADDR_ANY_INIT’ is provided to allow you to initialize your own variables to this value.  File: libc.info, Node: Host Address Functions, Next: Host Names, Prev: Host Address Data Type, Up: Host Addresses 16.6.2.3 Host Address Functions ............................... These additional functions for manipulating Internet addresses are declared in the header file ‘arpa/inet.h’. They represent Internet addresses in network byte order, and network numbers and local-address-within-network numbers in host byte order. *Note Byte Order::, for an explanation of network and host byte order. -- Function: int inet_aton (const char *NAME, struct in_addr *ADDR) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts the IPv4 Internet host address NAME from the standard numbers-and-dots notation into binary data and stores it in the ‘struct in_addr’ that ADDR points to. ‘inet_aton’ returns nonzero if the address is valid, zero if not. -- Function: uint32_t inet_addr (const char *NAME) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts the IPv4 Internet host address NAME from the standard numbers-and-dots notation into binary data. If the input is not valid, ‘inet_addr’ returns ‘INADDR_NONE’. This is an obsolete interface to ‘inet_aton’, described immediately above. It is obsolete because ‘INADDR_NONE’ is a valid address (255.255.255.255), and ‘inet_aton’ provides a cleaner way to indicate error return. -- Function: uint32_t inet_network (const char *NAME) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function extracts the network number from the address NAME, given in the standard numbers-and-dots notation. The returned address is in host order. If the input is not valid, ‘inet_network’ returns ‘-1’. The function works only with traditional IPv4 class A, B and C network types. It doesn't work with classless addresses and shouldn't be used anymore. -- Function: char * inet_ntoa (struct in_addr ADDR) Preliminary: | MT-Safe locale | AS-Unsafe race | AC-Safe | *Note POSIX Safety Concepts::. This function converts the IPv4 Internet host address ADDR to a string in the standard numbers-and-dots notation. The return value is a pointer into a statically-allocated buffer. Subsequent calls will overwrite the same buffer, so you should copy the string if you need to save it. In multi-threaded programs each thread has its own statically-allocated buffer. But still subsequent calls of ‘inet_ntoa’ in the same thread will overwrite the result of the last call. Instead of ‘inet_ntoa’ the newer function ‘inet_ntop’ which is described below should be used since it handles both IPv4 and IPv6 addresses. -- Function: struct in_addr inet_makeaddr (uint32_t NET, uint32_t LOCAL) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function makes an IPv4 Internet host address by combining the network number NET with the local-address-within-network number LOCAL. -- Function: uint32_t inet_lnaof (struct in_addr ADDR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the local-address-within-network part of the Internet host address ADDR. The function works only with traditional IPv4 class A, B and C network types. It doesn't work with classless addresses and shouldn't be used anymore. -- Function: uint32_t inet_netof (struct in_addr ADDR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the network number part of the Internet host address ADDR. The function works only with traditional IPv4 class A, B and C network types. It doesn't work with classless addresses and shouldn't be used anymore. -- Function: int inet_pton (int AF, const char *CP, void *BUF) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts an Internet address (either IPv4 or IPv6) from presentation (textual) to network (binary) format. AF should be either ‘AF_INET’ or ‘AF_INET6’, as appropriate for the type of address being converted. CP is a pointer to the input string, and BUF is a pointer to a buffer for the result. It is the caller's responsibility to make sure the buffer is large enough. -- Function: const char * inet_ntop (int AF, const void *CP, char *BUF, socklen_t LEN) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts an Internet address (either IPv4 or IPv6) from network (binary) to presentation (textual) form. AF should be either ‘AF_INET’ or ‘AF_INET6’, as appropriate. CP is a pointer to the address to be converted. BUF should be a pointer to a buffer to hold the result, and LEN is the length of this buffer. The return value from the function will be this buffer address.  File: libc.info, Node: Host Names, Prev: Host Address Functions, Up: Host Addresses 16.6.2.4 Host Names ................... Besides the standard numbers-and-dots notation for Internet addresses, you can also refer to a host by a symbolic name. The advantage of a symbolic name is that it is usually easier to remember. For example, the machine with Internet address ‘158.121.106.19’ is also known as ‘alpha.gnu.org’; and other machines in the ‘gnu.org’ domain can refer to it simply as ‘alpha’. Internally, the system uses a database to keep track of the mapping between host names and host numbers. This database is usually either the file ‘/etc/hosts’ or an equivalent provided by a name server. The functions and other symbols for accessing this database are declared in ‘netdb.h’. They are BSD features, defined unconditionally if you include ‘netdb.h’. -- Data Type: struct hostent This data type is used to represent an entry in the hosts database. It has the following members: ‘char *h_name’ This is the "official" name of the host. ‘char **h_aliases’ These are alternative names for the host, represented as a null-terminated vector of strings. ‘int h_addrtype’ This is the host address type; in practice, its value is always either ‘AF_INET’ or ‘AF_INET6’, with the latter being used for IPv6 hosts. In principle other kinds of addresses could be represented in the database as well as Internet addresses; if this were done, you might find a value in this field other than ‘AF_INET’ or ‘AF_INET6’. *Note Socket Addresses::. ‘int h_length’ This is the length, in bytes, of each address. ‘char **h_addr_list’ This is the vector of addresses for the host. (Recall that the host might be connected to multiple networks and have different addresses on each one.) The vector is terminated by a null pointer. ‘char *h_addr’ This is a synonym for ‘h_addr_list[0]’; in other words, it is the first host address. As far as the host database is concerned, each address is just a block of memory ‘h_length’ bytes long. But in other contexts there is an implicit assumption that you can convert IPv4 addresses to a ‘struct in_addr’ or an ‘uint32_t’. Host addresses in a ‘struct hostent’ structure are always given in network byte order; see *note Byte Order::. You can use ‘gethostbyname’, ‘gethostbyname2’ or ‘gethostbyaddr’ to search the hosts database for information about a particular host. The information is returned in a statically-allocated structure; you must copy the information if you need to save it across calls. You can also use ‘getaddrinfo’ and ‘getnameinfo’ to obtain this information. -- Function: struct hostent * gethostbyname (const char *NAME) Preliminary: | MT-Unsafe race:hostbyname env locale | AS-Unsafe dlopen plugin corrupt heap lock | AC-Unsafe lock corrupt mem fd | *Note POSIX Safety Concepts::. The ‘gethostbyname’ function returns information about the host named NAME. If the lookup fails, it returns a null pointer. -- Function: struct hostent * gethostbyname2 (const char *NAME, int AF) Preliminary: | MT-Unsafe race:hostbyname2 env locale | AS-Unsafe dlopen plugin corrupt heap lock | AC-Unsafe lock corrupt mem fd | *Note POSIX Safety Concepts::. The ‘gethostbyname2’ function is like ‘gethostbyname’, but allows the caller to specify the desired address family (e.g. ‘AF_INET’ or ‘AF_INET6’) of the result. -- Function: struct hostent * gethostbyaddr (const void *ADDR, socklen_t LENGTH, int FORMAT) Preliminary: | MT-Unsafe race:hostbyaddr env locale | AS-Unsafe dlopen plugin corrupt heap lock | AC-Unsafe lock corrupt mem fd | *Note POSIX Safety Concepts::. The ‘gethostbyaddr’ function returns information about the host with Internet address ADDR. The parameter ADDR is not really a pointer to char - it can be a pointer to an IPv4 or an IPv6 address. The LENGTH argument is the size (in bytes) of the address at ADDR. FORMAT specifies the address format; for an IPv4 Internet address, specify a value of ‘AF_INET’; for an IPv6 Internet address, use ‘AF_INET6’. If the lookup fails, ‘gethostbyaddr’ returns a null pointer. If the name lookup by ‘gethostbyname’ or ‘gethostbyaddr’ fails, you can find out the reason by looking at the value of the variable ‘h_errno’. (It would be cleaner design for these functions to set ‘errno’, but use of ‘h_errno’ is compatible with other systems.) Here are the error codes that you may find in ‘h_errno’: ‘HOST_NOT_FOUND’ No such host is known in the database. ‘TRY_AGAIN’ This condition happens when the name server could not be contacted. If you try again later, you may succeed then. ‘NO_RECOVERY’ A non-recoverable error occurred. ‘NO_ADDRESS’ The host database contains an entry for the name, but it doesn't have an associated Internet address. The lookup functions above all have one thing in common: they are not reentrant and therefore unusable in multi-threaded applications. Therefore provides the GNU C Library a new set of functions which can be used in this context. -- Function: int gethostbyname_r (const char *restrict NAME, struct hostent *restrict RESULT_BUF, char *restrict BUF, size_t BUFLEN, struct hostent **restrict RESULT, int *restrict H_ERRNOP) Preliminary: | MT-Safe env locale | AS-Unsafe dlopen plugin corrupt heap lock | AC-Unsafe lock corrupt mem fd | *Note POSIX Safety Concepts::. The ‘gethostbyname_r’ function returns information about the host named NAME. The caller must pass a pointer to an object of type ‘struct hostent’ in the RESULT_BUF parameter. In addition the function may need extra buffer space and the caller must pass a pointer and the size of the buffer in the BUF and BUFLEN parameters. A pointer to the buffer, in which the result is stored, is available in ‘*RESULT’ after the function call successfully returned. The buffer passed as the BUF parameter can be freed only once the caller has finished with the result hostent struct, or has copied it including all the other memory that it points to. If an error occurs or if no entry is found, the pointer ‘*RESULT’ is a null pointer. Success is signalled by a zero return value. If the function failed the return value is an error number. In addition to the errors defined for ‘gethostbyname’ it can also be ‘ERANGE’. In this case the call should be repeated with a larger buffer. Additional error information is not stored in the global variable ‘h_errno’ but instead in the object pointed to by H_ERRNOP. Here's a small example: struct hostent * gethostname (char *host) { struct hostent *hostbuf, *hp; size_t hstbuflen; char *tmphstbuf; int res; int herr; hostbuf = malloc (sizeof (struct hostent)); hstbuflen = 1024; tmphstbuf = malloc (hstbuflen); while ((res = gethostbyname_r (host, hostbuf, tmphstbuf, hstbuflen, &hp, &herr)) == ERANGE) { /* Enlarge the buffer. */ tmphstbuf = reallocarray (tmphstbuf, hstbuflen, 2); hstbuflen *= 2; } free (tmphstbuf); /* Check for errors. */ if (res || hp == NULL) return NULL; return hp; } -- Function: int gethostbyname2_r (const char *NAME, int AF, struct hostent *restrict RESULT_BUF, char *restrict BUF, size_t BUFLEN, struct hostent **restrict RESULT, int *restrict H_ERRNOP) Preliminary: | MT-Safe env locale | AS-Unsafe dlopen plugin corrupt heap lock | AC-Unsafe lock corrupt mem fd | *Note POSIX Safety Concepts::. The ‘gethostbyname2_r’ function is like ‘gethostbyname_r’, but allows the caller to specify the desired address family (e.g. ‘AF_INET’ or ‘AF_INET6’) for the result. -- Function: int gethostbyaddr_r (const void *ADDR, socklen_t LENGTH, int FORMAT, struct hostent *restrict RESULT_BUF, char *restrict BUF, size_t BUFLEN, struct hostent **restrict RESULT, int *restrict H_ERRNOP) Preliminary: | MT-Safe env locale | AS-Unsafe dlopen plugin corrupt heap lock | AC-Unsafe lock corrupt mem fd | *Note POSIX Safety Concepts::. The ‘gethostbyaddr_r’ function returns information about the host with Internet address ADDR. The parameter ADDR is not really a pointer to char - it can be a pointer to an IPv4 or an IPv6 address. The LENGTH argument is the size (in bytes) of the address at ADDR. FORMAT specifies the address format; for an IPv4 Internet address, specify a value of ‘AF_INET’; for an IPv6 Internet address, use ‘AF_INET6’. Similar to the ‘gethostbyname_r’ function, the caller must provide buffers for the result and memory used internally. In case of success the function returns zero. Otherwise the value is an error number where ‘ERANGE’ has the special meaning that the caller-provided buffer is too small. You can also scan the entire hosts database one entry at a time using ‘sethostent’, ‘gethostent’ and ‘endhostent’. Be careful when using these functions because they are not reentrant. -- Function: void sethostent (int STAYOPEN) Preliminary: | MT-Unsafe race:hostent env locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function opens the hosts database to begin scanning it. You can then call ‘gethostent’ to read the entries. If the STAYOPEN argument is nonzero, this sets a flag so that subsequent calls to ‘gethostbyname’ or ‘gethostbyaddr’ will not close the database (as they usually would). This makes for more efficiency if you call those functions several times, by avoiding reopening the database for each call. -- Function: struct hostent * gethostent (void) Preliminary: | MT-Unsafe race:hostent race:hostentbuf env locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function returns the next entry in the hosts database. It returns a null pointer if there are no more entries. -- Function: void endhostent (void) Preliminary: | MT-Unsafe race:hostent env locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function closes the hosts database.  File: libc.info, Node: Ports, Next: Services Database, Prev: Host Addresses, Up: Internet Namespace 16.6.3 Internet Ports --------------------- A socket address in the Internet namespace consists of a machine's Internet address plus a “port number” which distinguishes the sockets on a given machine (for a given protocol). Port numbers range from 0 to 65,535. Port numbers less than ‘IPPORT_RESERVED’ are reserved for standard servers, such as ‘finger’ and ‘telnet’. There is a database that keeps track of these, and you can use the ‘getservbyname’ function to map a service name onto a port number; see *note Services Database::. If you write a server that is not one of the standard ones defined in the database, you must choose a port number for it. Use a number greater than ‘IPPORT_USERRESERVED’; such numbers are reserved for servers and won't ever be generated automatically by the system. Avoiding conflicts with servers being run by other users is up to you. When you use a socket without specifying its address, the system generates a port number for it. This number is between ‘IPPORT_RESERVED’ and ‘IPPORT_USERRESERVED’. On the Internet, it is actually legitimate to have two different sockets with the same port number, as long as they never both try to communicate with the same socket address (host address plus port number). You shouldn't duplicate a port number except in special circumstances where a higher-level protocol requires it. Normally, the system won't let you do it; ‘bind’ normally insists on distinct port numbers. To reuse a port number, you must set the socket option ‘SO_REUSEADDR’. *Note Socket-Level Options::. These macros are defined in the header file ‘netinet/in.h’. -- Macro: int IPPORT_RESERVED Port numbers less than ‘IPPORT_RESERVED’ are reserved for superuser use. -- Macro: int IPPORT_USERRESERVED Port numbers greater than or equal to ‘IPPORT_USERRESERVED’ are reserved for explicit use; they will never be allocated automatically.  File: libc.info, Node: Services Database, Next: Byte Order, Prev: Ports, Up: Internet Namespace 16.6.4 The Services Database ---------------------------- The database that keeps track of "well-known" services is usually either the file ‘/etc/services’ or an equivalent from a name server. You can use these utilities, declared in ‘netdb.h’, to access the services database. -- Data Type: struct servent This data type holds information about entries from the services database. It has the following members: ‘char *s_name’ This is the "official" name of the service. ‘char **s_aliases’ These are alternate names for the service, represented as an array of strings. A null pointer terminates the array. ‘int s_port’ This is the port number for the service. Port numbers are given in network byte order; see *note Byte Order::. ‘char *s_proto’ This is the name of the protocol to use with this service. *Note Protocols Database::. To get information about a particular service, use the ‘getservbyname’ or ‘getservbyport’ functions. The information is returned in a statically-allocated structure; you must copy the information if you need to save it across calls. -- Function: struct servent * getservbyname (const char *NAME, const char *PROTO) Preliminary: | MT-Unsafe race:servbyname locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘getservbyname’ function returns information about the service named NAME using protocol PROTO. If it can't find such a service, it returns a null pointer. This function is useful for servers as well as for clients; servers use it to determine which port they should listen on (*note Listening::). -- Function: struct servent * getservbyport (int PORT, const char *PROTO) Preliminary: | MT-Unsafe race:servbyport locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘getservbyport’ function returns information about the service at port PORT using protocol PROTO. If it can't find such a service, it returns a null pointer. You can also scan the services database using ‘setservent’, ‘getservent’ and ‘endservent’. Be careful when using these functions because they are not reentrant. -- Function: void setservent (int STAYOPEN) Preliminary: | MT-Unsafe race:servent locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function opens the services database to begin scanning it. If the STAYOPEN argument is nonzero, this sets a flag so that subsequent calls to ‘getservbyname’ or ‘getservbyport’ will not close the database (as they usually would). This makes for more efficiency if you call those functions several times, by avoiding reopening the database for each call. -- Function: struct servent * getservent (void) Preliminary: | MT-Unsafe race:servent race:serventbuf locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function returns the next entry in the services database. If there are no more entries, it returns a null pointer. -- Function: void endservent (void) Preliminary: | MT-Unsafe race:servent locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function closes the services database.  File: libc.info, Node: Byte Order, Next: Protocols Database, Prev: Services Database, Up: Internet Namespace 16.6.5 Byte Order Conversion ---------------------------- Different kinds of computers use different conventions for the ordering of bytes within a word. Some computers put the most significant byte within a word first (this is called "big-endian" order), and others put it last ("little-endian" order). So that machines with different byte order conventions can communicate, the Internet protocols specify a canonical byte order convention for data transmitted over the network. This is known as “network byte order”. When establishing an Internet socket connection, you must make sure that the data in the ‘sin_port’ and ‘sin_addr’ members of the ‘sockaddr_in’ structure are represented in network byte order. If you are encoding integer data in the messages sent through the socket, you should convert this to network byte order too. If you don't do this, your program may fail when running on or talking to other kinds of machines. If you use ‘getservbyname’ and ‘gethostbyname’ or ‘inet_addr’ to get the port number and host address, the values are already in network byte order, and you can copy them directly into the ‘sockaddr_in’ structure. Otherwise, you have to convert the values explicitly. Use ‘htons’ and ‘ntohs’ to convert values for the ‘sin_port’ member. Use ‘htonl’ and ‘ntohl’ to convert IPv4 addresses for the ‘sin_addr’ member. (Remember, ‘struct in_addr’ is equivalent to ‘uint32_t’.) These functions are declared in ‘netinet/in.h’. -- Function: uint16_t htons (uint16_t HOSTSHORT) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts the ‘uint16_t’ integer HOSTSHORT from host byte order to network byte order. -- Function: uint16_t ntohs (uint16_t NETSHORT) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts the ‘uint16_t’ integer NETSHORT from network byte order to host byte order. -- Function: uint32_t htonl (uint32_t HOSTLONG) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts the ‘uint32_t’ integer HOSTLONG from host byte order to network byte order. This is used for IPv4 Internet addresses. -- Function: uint32_t ntohl (uint32_t NETLONG) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function converts the ‘uint32_t’ integer NETLONG from network byte order to host byte order. This is used for IPv4 Internet addresses.  File: libc.info, Node: Protocols Database, Next: Inet Example, Prev: Byte Order, Up: Internet Namespace 16.6.6 Protocols Database ------------------------- The communications protocol used with a socket controls low-level details of how data are exchanged. For example, the protocol implements things like checksums to detect errors in transmissions, and routing instructions for messages. Normal user programs have little reason to mess with these details directly. The default communications protocol for the Internet namespace depends on the communication style. For stream communication, the default is TCP ("transmission control protocol"). For datagram communication, the default is UDP ("user datagram protocol"). For reliable datagram communication, the default is RDP ("reliable datagram protocol"). You should nearly always use the default. Internet protocols are generally specified by a name instead of a number. The network protocols that a host knows about are stored in a database. This is usually either derived from the file ‘/etc/protocols’, or it may be an equivalent provided by a name server. You look up the protocol number associated with a named protocol in the database using the ‘getprotobyname’ function. Here are detailed descriptions of the utilities for accessing the protocols database. These are declared in ‘netdb.h’. -- Data Type: struct protoent This data type is used to represent entries in the network protocols database. It has the following members: ‘char *p_name’ This is the official name of the protocol. ‘char **p_aliases’ These are alternate names for the protocol, specified as an array of strings. The last element of the array is a null pointer. ‘int p_proto’ This is the protocol number (in host byte order); use this member as the PROTOCOL argument to ‘socket’. You can use ‘getprotobyname’ and ‘getprotobynumber’ to search the protocols database for a specific protocol. The information is returned in a statically-allocated structure; you must copy the information if you need to save it across calls. -- Function: struct protoent * getprotobyname (const char *NAME) Preliminary: | MT-Unsafe race:protobyname locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘getprotobyname’ function returns information about the network protocol named NAME. If there is no such protocol, it returns a null pointer. -- Function: struct protoent * getprotobynumber (int PROTOCOL) Preliminary: | MT-Unsafe race:protobynumber locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘getprotobynumber’ function returns information about the network protocol with number PROTOCOL. If there is no such protocol, it returns a null pointer. You can also scan the whole protocols database one protocol at a time by using ‘setprotoent’, ‘getprotoent’ and ‘endprotoent’. Be careful when using these functions because they are not reentrant. -- Function: void setprotoent (int STAYOPEN) Preliminary: | MT-Unsafe race:protoent locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function opens the protocols database to begin scanning it. If the STAYOPEN argument is nonzero, this sets a flag so that subsequent calls to ‘getprotobyname’ or ‘getprotobynumber’ will not close the database (as they usually would). This makes for more efficiency if you call those functions several times, by avoiding reopening the database for each call. -- Function: struct protoent * getprotoent (void) Preliminary: | MT-Unsafe race:protoent race:protoentbuf locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function returns the next entry in the protocols database. It returns a null pointer if there are no more entries. -- Function: void endprotoent (void) Preliminary: | MT-Unsafe race:protoent locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function closes the protocols database.  File: libc.info, Node: Inet Example, Prev: Protocols Database, Up: Internet Namespace 16.6.7 Internet Socket Example ------------------------------ Here is an example showing how to create and name a socket in the Internet namespace. The newly created socket exists on the machine that the program is running on. Rather than finding and using the machine's Internet address, this example specifies ‘INADDR_ANY’ as the host address; the system replaces that with the machine's actual address. #include #include #include #include int make_socket (uint16_t port) { int sock; struct sockaddr_in name; /* Create the socket. */ sock = socket (PF_INET, SOCK_STREAM, 0); if (sock < 0) { perror ("socket"); exit (EXIT_FAILURE); } /* Give the socket a name. */ name.sin_family = AF_INET; name.sin_port = htons (port); name.sin_addr.s_addr = htonl (INADDR_ANY); if (bind (sock, (struct sockaddr *) &name, sizeof (name)) < 0) { perror ("bind"); exit (EXIT_FAILURE); } return sock; } Here is another example, showing how you can fill in a ‘sockaddr_in’ structure, given a host name string and a port number: #include #include #include #include #include void init_sockaddr (struct sockaddr_in *name, const char *hostname, uint16_t port) { struct hostent *hostinfo; name->sin_family = AF_INET; name->sin_port = htons (port); hostinfo = gethostbyname (hostname); if (hostinfo == NULL) { fprintf (stderr, "Unknown host %s.\n", hostname); exit (EXIT_FAILURE); } name->sin_addr = *(struct in_addr *) hostinfo->h_addr; }  File: libc.info, Node: Misc Namespaces, Next: Open/Close Sockets, Prev: Internet Namespace, Up: Sockets 16.7 Other Namespaces ===================== Certain other namespaces and associated protocol families are supported but not documented yet because they are not often used. ‘PF_NS’ refers to the Xerox Network Software protocols. ‘PF_ISO’ stands for Open Systems Interconnect. ‘PF_CCITT’ refers to protocols from CCITT. ‘socket.h’ defines these symbols and others naming protocols not actually implemented. ‘PF_IMPLINK’ is used for communicating between hosts and Internet Message Processors. For information on this and ‘PF_ROUTE’, an occasionally-used local area routing protocol, see the GNU Hurd Manual (to appear in the future).  File: libc.info, Node: Open/Close Sockets, Next: Connections, Prev: Misc Namespaces, Up: Sockets 16.8 Opening and Closing Sockets ================================ This section describes the actual library functions for opening and closing sockets. The same functions work for all namespaces and connection styles. * Menu: * Creating a Socket:: How to open a socket. * Closing a Socket:: How to close a socket. * Socket Pairs:: These are created like pipes.  File: libc.info, Node: Creating a Socket, Next: Closing a Socket, Up: Open/Close Sockets 16.8.1 Creating a Socket ------------------------ The primitive for creating a socket is the ‘socket’ function, declared in ‘sys/socket.h’. -- Function: int socket (int NAMESPACE, int STYLE, int PROTOCOL) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. This function creates a socket and specifies communication style STYLE, which should be one of the socket styles listed in *note Communication Styles::. The NAMESPACE argument specifies the namespace; it must be ‘PF_LOCAL’ (*note Local Namespace::) or ‘PF_INET’ (*note Internet Namespace::). PROTOCOL designates the specific protocol (*note Socket Concepts::); zero is usually right for PROTOCOL. The return value from ‘socket’ is the file descriptor for the new socket, or ‘-1’ in case of error. The following ‘errno’ error conditions are defined for this function: ‘EPROTONOSUPPORT’ The PROTOCOL or STYLE is not supported by the NAMESPACE specified. ‘EMFILE’ The process already has too many file descriptors open. ‘ENFILE’ The system already has too many file descriptors open. ‘EACCES’ The process does not have the privilege to create a socket of the specified STYLE or PROTOCOL. ‘ENOBUFS’ The system ran out of internal buffer space. The file descriptor returned by the ‘socket’ function supports both read and write operations. However, like pipes, sockets do not support file positioning operations. For examples of how to call the ‘socket’ function, see *note Local Socket Example::, or *note Inet Example::.  File: libc.info, Node: Closing a Socket, Next: Socket Pairs, Prev: Creating a Socket, Up: Open/Close Sockets 16.8.2 Closing a Socket ----------------------- When you have finished using a socket, you can simply close its file descriptor with ‘close’; see *note Opening and Closing Files::. If there is still data waiting to be transmitted over the connection, normally ‘close’ tries to complete this transmission. You can control this behavior using the ‘SO_LINGER’ socket option to specify a timeout period; see *note Socket Options::. You can also shut down only reception or transmission on a connection by calling ‘shutdown’, which is declared in ‘sys/socket.h’. -- Function: int shutdown (int SOCKET, int HOW) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘shutdown’ function shuts down the connection of socket SOCKET. The argument HOW specifies what action to perform: ‘0’ Stop receiving data for this socket. If further data arrives, reject it. ‘1’ Stop trying to transmit data from this socket. Discard any data waiting to be sent. Stop looking for acknowledgement of data already sent; don't retransmit it if it is lost. ‘2’ Stop both reception and transmission. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ SOCKET is not a valid file descriptor. ‘ENOTSOCK’ SOCKET is not a socket. ‘ENOTCONN’ SOCKET is not connected.  File: libc.info, Node: Socket Pairs, Prev: Closing a Socket, Up: Open/Close Sockets 16.8.3 Socket Pairs ------------------- A “socket pair” consists of a pair of connected (but unnamed) sockets. It is very similar to a pipe and is used in much the same way. Socket pairs are created with the ‘socketpair’ function, declared in ‘sys/socket.h’. A socket pair is much like a pipe; the main difference is that the socket pair is bidirectional, whereas the pipe has one input-only end and one output-only end (*note Pipes and FIFOs::). -- Function: int socketpair (int NAMESPACE, int STYLE, int PROTOCOL, int FILEDES[2]) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. This function creates a socket pair, returning the file descriptors in ‘FILEDES[0]’ and ‘FILEDES[1]’. The socket pair is a full-duplex communications channel, so that both reading and writing may be performed at either end. The NAMESPACE, STYLE and PROTOCOL arguments are interpreted as for the ‘socket’ function. STYLE should be one of the communication styles listed in *note Communication Styles::. The NAMESPACE argument specifies the namespace, which must be ‘AF_LOCAL’ (*note Local Namespace::); PROTOCOL specifies the communications protocol, but zero is the only meaningful value. If STYLE specifies a connectionless communication style, then the two sockets you get are not _connected_, strictly speaking, but each of them knows the other as the default destination address, so they can send packets to each other. The ‘socketpair’ function returns ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EMFILE’ The process has too many file descriptors open. ‘EAFNOSUPPORT’ The specified namespace is not supported. ‘EPROTONOSUPPORT’ The specified protocol is not supported. ‘EOPNOTSUPP’ The specified protocol does not support the creation of socket pairs.  File: libc.info, Node: Connections, Next: Datagrams, Prev: Open/Close Sockets, Up: Sockets 16.9 Using Sockets with Connections =================================== The most common communication styles involve making a connection to a particular other socket, and then exchanging data with that socket over and over. Making a connection is asymmetric; one side (the “client”) acts to request a connection, while the other side (the “server”) makes a socket and waits for the connection request. * Menu: * Connecting:: What the client program must do. * Listening:: How a server program waits for requests. * Accepting Connections:: What the server does when it gets a request. * Who is Connected:: Getting the address of the other side of a connection. * Transferring Data:: How to send and receive data. * Byte Stream Example:: An example program: a client for communicating over a byte stream socket in the Internet namespace. * Server Example:: A corresponding server program. * Out-of-Band Data:: This is an advanced feature.  File: libc.info, Node: Connecting, Next: Listening, Up: Connections 16.9.1 Making a Connection -------------------------- In making a connection, the client makes a connection while the server waits for and accepts the connection. Here we discuss what the client program must do with the ‘connect’ function, which is declared in ‘sys/socket.h’. -- Function: int connect (int SOCKET, struct sockaddr *ADDR, socklen_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘connect’ function initiates a connection from the socket with file descriptor SOCKET to the socket whose address is specified by the ADDR and LENGTH arguments. (This socket is typically on another machine, and it must be already set up as a server.) *Note Socket Addresses::, for information about how these arguments are interpreted. Normally, ‘connect’ waits until the server responds to the request before it returns. You can set nonblocking mode on the socket SOCKET to make ‘connect’ return immediately without waiting for the response. *Note File Status Flags::, for information about nonblocking mode. The normal return value from ‘connect’ is ‘0’. If an error occurs, ‘connect’ returns ‘-1’. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The socket SOCKET is not a valid file descriptor. ‘ENOTSOCK’ File descriptor SOCKET is not a socket. ‘EADDRNOTAVAIL’ The specified address is not available on the remote machine. ‘EAFNOSUPPORT’ The namespace of the ADDR is not supported by this socket. ‘EISCONN’ The socket SOCKET is already connected. ‘ETIMEDOUT’ The attempt to establish the connection timed out. ‘ECONNREFUSED’ The server has actively refused to establish the connection. ‘ENETUNREACH’ The network of the given ADDR isn't reachable from this host. ‘EADDRINUSE’ The socket address of the given ADDR is already in use. ‘EINPROGRESS’ The socket SOCKET is non-blocking and the connection could not be established immediately. You can determine when the connection is completely established with ‘select’; *note Waiting for I/O::. Another ‘connect’ call on the same socket, before the connection is completely established, will fail with ‘EALREADY’. ‘EALREADY’ The socket SOCKET is non-blocking and already has a pending connection in progress (see ‘EINPROGRESS’ above). This function is defined as a cancellation point in multi-threaded programs, so one has to be prepared for this and make sure that allocated resources (like memory, file descriptors, semaphores or whatever) are freed even if the thread is canceled.  File: libc.info, Node: Listening, Next: Accepting Connections, Prev: Connecting, Up: Connections 16.9.2 Listening for Connections -------------------------------- Now let us consider what the server process must do to accept connections on a socket. First it must use the ‘listen’ function to enable connection requests on the socket, and then accept each incoming connection with a call to ‘accept’ (*note Accepting Connections::). Once connection requests are enabled on a server socket, the ‘select’ function reports when the socket has a connection ready to be accepted (*note Waiting for I/O::). The ‘listen’ function is not allowed for sockets using connectionless communication styles. You can write a network server that does not even start running until a connection to it is requested. *Note Inetd Servers::. In the Internet namespace, there are no special protection mechanisms for controlling access to a port; any process on any machine can make a connection to your server. If you want to restrict access to your server, make it examine the addresses associated with connection requests or implement some other handshaking or identification protocol. In the local namespace, the ordinary file protection bits control who has access to connect to the socket. -- Function: int listen (int SOCKET, int N) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. The ‘listen’ function enables the socket SOCKET to accept connections, thus making it a server socket. The argument N specifies the length of the queue for pending connections. When the queue fills, new clients attempting to connect fail with ‘ECONNREFUSED’ until the server calls ‘accept’ to accept a connection from the queue. The ‘listen’ function returns ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The argument SOCKET is not a valid file descriptor. ‘ENOTSOCK’ The argument SOCKET is not a socket. ‘EOPNOTSUPP’ The socket SOCKET does not support this operation.  File: libc.info, Node: Accepting Connections, Next: Who is Connected, Prev: Listening, Up: Connections 16.9.3 Accepting Connections ---------------------------- When a server receives a connection request, it can complete the connection by accepting the request. Use the function ‘accept’ to do this. A socket that has been established as a server can accept connection requests from multiple clients. The server's original socket _does not become part of the connection_; instead, ‘accept’ makes a new socket which participates in the connection. ‘accept’ returns the descriptor for this socket. The server's original socket remains available for listening for further connection requests. The number of pending connection requests on a server socket is finite. If connection requests arrive from clients faster than the server can act upon them, the queue can fill up and additional requests are refused with an ‘ECONNREFUSED’ error. You can specify the maximum length of this queue as an argument to the ‘listen’ function, although the system may also impose its own internal limit on the length of this queue. -- Function: int accept (int SOCKET, struct sockaddr *ADDR, socklen_t *LENGTH_PTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. This function is used to accept a connection request on the server socket SOCKET. The ‘accept’ function waits if there are no connections pending, unless the socket SOCKET has nonblocking mode set. (You can use ‘select’ to wait for a pending connection, with a nonblocking socket.) *Note File Status Flags::, for information about nonblocking mode. The ADDR and LENGTH-PTR arguments are used to return information about the name of the client socket that initiated the connection. *Note Socket Addresses::, for information about the format of the information. Accepting a connection does not make SOCKET part of the connection. Instead, it creates a new socket which becomes connected. The normal return value of ‘accept’ is the file descriptor for the new socket. After ‘accept’, the original socket SOCKET remains open and unconnected, and continues listening until you close it. You can accept further connections with SOCKET by calling ‘accept’ again. If an error occurs, ‘accept’ returns ‘-1’. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The SOCKET argument is not a valid file descriptor. ‘ENOTSOCK’ The descriptor SOCKET argument is not a socket. ‘EOPNOTSUPP’ The descriptor SOCKET does not support this operation. ‘EWOULDBLOCK’ SOCKET has nonblocking mode set, and there are no pending connections immediately available. This function is defined as a cancellation point in multi-threaded programs, so one has to be prepared for this and make sure that allocated resources (like memory, file descriptors, semaphores or whatever) are freed even if the thread is canceled. The ‘accept’ function is not allowed for sockets using connectionless communication styles.  File: libc.info, Node: Who is Connected, Next: Transferring Data, Prev: Accepting Connections, Up: Connections 16.9.4 Who is Connected to Me? ------------------------------ -- Function: int getpeername (int SOCKET, struct sockaddr *ADDR, socklen_t *LENGTH-PTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘getpeername’ function returns the address of the socket that SOCKET is connected to; it stores the address in the memory space specified by ADDR and LENGTH-PTR. It stores the length of the address in ‘*LENGTH-PTR’. *Note Socket Addresses::, for information about the format of the address. In some operating systems, ‘getpeername’ works only for sockets in the Internet domain. The return value is ‘0’ on success and ‘-1’ on error. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The argument SOCKET is not a valid file descriptor. ‘ENOTSOCK’ The descriptor SOCKET is not a socket. ‘ENOTCONN’ The socket SOCKET is not connected. ‘ENOBUFS’ There are not enough internal buffers available.  File: libc.info, Node: Transferring Data, Next: Byte Stream Example, Prev: Who is Connected, Up: Connections 16.9.5 Transferring Data ------------------------ Once a socket has been connected to a peer, you can use the ordinary ‘read’ and ‘write’ operations (*note I/O Primitives::) to transfer data. A socket is a two-way communications channel, so read and write operations can be performed at either end. There are also some I/O modes that are specific to socket operations. In order to specify these modes, you must use the ‘recv’ and ‘send’ functions instead of the more generic ‘read’ and ‘write’ functions. The ‘recv’ and ‘send’ functions take an additional argument which you can use to specify various flags to control special I/O modes. For example, you can specify the ‘MSG_OOB’ flag to read or write out-of-band data, the ‘MSG_PEEK’ flag to peek at input, or the ‘MSG_DONTROUTE’ flag to control inclusion of routing information on output. * Menu: * Sending Data:: Sending data with ‘send’. * Receiving Data:: Reading data with ‘recv’. * Socket Data Options:: Using ‘send’ and ‘recv’.  File: libc.info, Node: Sending Data, Next: Receiving Data, Up: Transferring Data 16.9.5.1 Sending Data ..................... The ‘send’ function is declared in the header file ‘sys/socket.h’. If your FLAGS argument is zero, you can just as well use ‘write’ instead of ‘send’; see *note I/O Primitives::. If the socket was connected but the connection has broken, you get a ‘SIGPIPE’ signal for any use of ‘send’ or ‘write’ (*note Miscellaneous Signals::). -- Function: ssize_t send (int SOCKET, const void *BUFFER, size_t SIZE, int FLAGS) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘send’ function is like ‘write’, but with the additional flags FLAGS. The possible values of FLAGS are described in *note Socket Data Options::. This function returns the number of bytes transmitted, or ‘-1’ on failure. If the socket is nonblocking, then ‘send’ (like ‘write’) can return after sending just part of the data. *Note File Status Flags::, for information about nonblocking mode. Note, however, that a successful return value merely indicates that the message has been sent without error, not necessarily that it has been received without error. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The SOCKET argument is not a valid file descriptor. ‘EINTR’ The operation was interrupted by a signal before any data was sent. *Note Interrupted Primitives::. ‘ENOTSOCK’ The descriptor SOCKET is not a socket. ‘EMSGSIZE’ The socket type requires that the message be sent atomically, but the message is too large for this to be possible. ‘EWOULDBLOCK’ Nonblocking mode has been set on the socket, and the write operation would block. (Normally ‘send’ blocks until the operation can be completed.) ‘ENOBUFS’ There is not enough internal buffer space available. ‘ENOTCONN’ You never connected this socket. ‘EPIPE’ This socket was connected but the connection is now broken. In this case, ‘send’ generates a ‘SIGPIPE’ signal first; if that signal is ignored or blocked, or if its handler returns, then ‘send’ fails with ‘EPIPE’. This function is defined as a cancellation point in multi-threaded programs, so one has to be prepared for this and make sure that allocated resources (like memory, file descriptors, semaphores or whatever) are freed even if the thread is canceled.  File: libc.info, Node: Receiving Data, Next: Socket Data Options, Prev: Sending Data, Up: Transferring Data 16.9.5.2 Receiving Data ....................... The ‘recv’ function is declared in the header file ‘sys/socket.h’. If your FLAGS argument is zero, you can just as well use ‘read’ instead of ‘recv’; see *note I/O Primitives::. -- Function: ssize_t recv (int SOCKET, void *BUFFER, size_t SIZE, int FLAGS) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘recv’ function is like ‘read’, but with the additional flags FLAGS. The possible values of FLAGS are described in *note Socket Data Options::. If nonblocking mode is set for SOCKET, and no data are available to be read, ‘recv’ fails immediately rather than waiting. *Note File Status Flags::, for information about nonblocking mode. This function returns the number of bytes received, or ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The SOCKET argument is not a valid file descriptor. ‘ENOTSOCK’ The descriptor SOCKET is not a socket. ‘EWOULDBLOCK’ Nonblocking mode has been set on the socket, and the read operation would block. (Normally, ‘recv’ blocks until there is input available to be read.) ‘EINTR’ The operation was interrupted by a signal before any data was read. *Note Interrupted Primitives::. ‘ENOTCONN’ You never connected this socket. This function is defined as a cancellation point in multi-threaded programs, so one has to be prepared for this and make sure that allocated resources (like memory, file descriptors, semaphores or whatever) are freed even if the thread is canceled.  File: libc.info, Node: Socket Data Options, Prev: Receiving Data, Up: Transferring Data 16.9.5.3 Socket Data Options ............................ The FLAGS argument to ‘send’ and ‘recv’ is a bit mask. You can bitwise-OR the values of the following macros together to obtain a value for this argument. All are defined in the header file ‘sys/socket.h’. -- Macro: int MSG_OOB Send or receive out-of-band data. *Note Out-of-Band Data::. -- Macro: int MSG_PEEK Look at the data but don't remove it from the input queue. This is only meaningful with input functions such as ‘recv’, not with ‘send’. -- Macro: int MSG_DONTROUTE Don't include routing information in the message. This is only meaningful with output operations, and is usually only of interest for diagnostic or routing programs. We don't try to explain it here.  File: libc.info, Node: Byte Stream Example, Next: Server Example, Prev: Transferring Data, Up: Connections 16.9.6 Byte Stream Socket Example --------------------------------- Here is an example client program that makes a connection for a byte stream socket in the Internet namespace. It doesn't do anything particularly interesting once it has connected to the server; it just sends a text string to the server and exits. This program uses ‘init_sockaddr’ to set up the socket address; see *note Inet Example::. #include #include #include #include #include #include #include #include #define PORT 5555 #define MESSAGE "Yow!!! Are we having fun yet?!?" #define SERVERHOST "www.gnu.org" void write_to_server (int filedes) { int nbytes; nbytes = write (filedes, MESSAGE, strlen (MESSAGE) + 1); if (nbytes < 0) { perror ("write"); exit (EXIT_FAILURE); } } int main (void) { extern void init_sockaddr (struct sockaddr_in *name, const char *hostname, uint16_t port); int sock; struct sockaddr_in servername; /* Create the socket. */ sock = socket (PF_INET, SOCK_STREAM, 0); if (sock < 0) { perror ("socket (client)"); exit (EXIT_FAILURE); } /* Connect to the server. */ init_sockaddr (&servername, SERVERHOST, PORT); if (0 > connect (sock, (struct sockaddr *) &servername, sizeof (servername))) { perror ("connect (client)"); exit (EXIT_FAILURE); } /* Send data to the server. */ write_to_server (sock); close (sock); exit (EXIT_SUCCESS); }  File: libc.info, Node: Server Example, Next: Out-of-Band Data, Prev: Byte Stream Example, Up: Connections 16.9.7 Byte Stream Connection Server Example -------------------------------------------- The server end is much more complicated. Since we want to allow multiple clients to be connected to the server at the same time, it would be incorrect to wait for input from a single client by simply calling ‘read’ or ‘recv’. Instead, the right thing to do is to use ‘select’ (*note Waiting for I/O::) to wait for input on all of the open sockets. This also allows the server to deal with additional connection requests. This particular server doesn't do anything interesting once it has gotten a message from a client. It does close the socket for that client when it detects an end-of-file condition (resulting from the client shutting down its end of the connection). This program uses ‘make_socket’ to set up the socket address; see *note Inet Example::. #include #include #include #include #include #include #include #include #define PORT 5555 #define MAXMSG 512 int read_from_client (int filedes) { char buffer[MAXMSG]; int nbytes; nbytes = read (filedes, buffer, MAXMSG); if (nbytes < 0) { /* Read error. */ perror ("read"); exit (EXIT_FAILURE); } else if (nbytes == 0) /* End-of-file. */ return -1; else { /* Data read. */ fprintf (stderr, "Server: got message: `%s'\n", buffer); return 0; } } int main (void) { extern int make_socket (uint16_t port); int sock; fd_set active_fd_set, read_fd_set; int i; struct sockaddr_in clientname; size_t size; /* Create the socket and set it up to accept connections. */ sock = make_socket (PORT); if (listen (sock, 1) < 0) { perror ("listen"); exit (EXIT_FAILURE); } /* Initialize the set of active sockets. */ FD_ZERO (&active_fd_set); FD_SET (sock, &active_fd_set); while (1) { /* Block until input arrives on one or more active sockets. */ read_fd_set = active_fd_set; if (select (FD_SETSIZE, &read_fd_set, NULL, NULL, NULL) < 0) { perror ("select"); exit (EXIT_FAILURE); } /* Service all the sockets with input pending. */ for (i = 0; i < FD_SETSIZE; ++i) if (FD_ISSET (i, &read_fd_set)) { if (i == sock) { /* Connection request on original socket. */ int new; size = sizeof (clientname); new = accept (sock, (struct sockaddr *) &clientname, &size); if (new < 0) { perror ("accept"); exit (EXIT_FAILURE); } fprintf (stderr, "Server: connect from host %s, port %hd.\n", inet_ntoa (clientname.sin_addr), ntohs (clientname.sin_port)); FD_SET (new, &active_fd_set); } else { /* Data arriving on an already-connected socket. */ if (read_from_client (i) < 0) { close (i); FD_CLR (i, &active_fd_set); } } } } }  File: libc.info, Node: Out-of-Band Data, Prev: Server Example, Up: Connections 16.9.8 Out-of-Band Data ----------------------- Streams with connections permit “out-of-band” data that is delivered with higher priority than ordinary data. Typically the reason for sending out-of-band data is to send notice of an exceptional condition. To send out-of-band data use ‘send’, specifying the flag ‘MSG_OOB’ (*note Sending Data::). Out-of-band data are received with higher priority because the receiving process need not read it in sequence; to read the next available out-of-band data, use ‘recv’ with the ‘MSG_OOB’ flag (*note Receiving Data::). Ordinary read operations do not read out-of-band data; they read only ordinary data. When a socket finds that out-of-band data are on their way, it sends a ‘SIGURG’ signal to the owner process or process group of the socket. You can specify the owner using the ‘F_SETOWN’ command to the ‘fcntl’ function; see *note Interrupt Input::. You must also establish a handler for this signal, as described in *note Signal Handling::, in order to take appropriate action such as reading the out-of-band data. Alternatively, you can test for pending out-of-band data, or wait until there is out-of-band data, using the ‘select’ function; it can wait for an exceptional condition on the socket. *Note Waiting for I/O::, for more information about ‘select’. Notification of out-of-band data (whether with ‘SIGURG’ or with ‘select’) indicates that out-of-band data are on the way; the data may not actually arrive until later. If you try to read the out-of-band data before it arrives, ‘recv’ fails with an ‘EWOULDBLOCK’ error. Sending out-of-band data automatically places a "mark" in the stream of ordinary data, showing where in the sequence the out-of-band data "would have been". This is useful when the meaning of out-of-band data is "cancel everything sent so far". Here is how you can test, in the receiving process, whether any ordinary data was sent before the mark: success = ioctl (socket, SIOCATMARK, &atmark); The ‘integer’ variable ATMARK is set to a nonzero value if the socket's read pointer has reached the "mark". Here's a function to discard any ordinary data preceding the out-of-band mark: int discard_until_mark (int socket) { while (1) { /* This is not an arbitrary limit; any size will do. */ char buffer[1024]; int atmark, success; /* If we have reached the mark, return. */ success = ioctl (socket, SIOCATMARK, &atmark); if (success < 0) perror ("ioctl"); if (result) return; /* Otherwise, read a bunch of ordinary data and discard it. This is guaranteed not to read past the mark if it starts before the mark. */ success = read (socket, buffer, sizeof buffer); if (success < 0) perror ("read"); } } If you don't want to discard the ordinary data preceding the mark, you may need to read some of it anyway, to make room in internal system buffers for the out-of-band data. If you try to read out-of-band data and get an ‘EWOULDBLOCK’ error, try reading some ordinary data (saving it so that you can use it when you want it) and see if that makes room. Here is an example: struct buffer { char *buf; int size; struct buffer *next; }; /* Read the out-of-band data from SOCKET and return it as a 'struct buffer', which records the address of the data and its size. It may be necessary to read some ordinary data in order to make room for the out-of-band data. If so, the ordinary data are saved as a chain of buffers found in the 'next' field of the value. */ struct buffer * read_oob (int socket) { struct buffer *tail = 0; struct buffer *list = 0; while (1) { /* This is an arbitrary limit. Does anyone know how to do this without a limit? */ #define BUF_SZ 1024 char *buf = (char *) xmalloc (BUF_SZ); int success; int atmark; /* Try again to read the out-of-band data. */ success = recv (socket, buf, BUF_SZ, MSG_OOB); if (success >= 0) { /* We got it, so return it. */ struct buffer *link = (struct buffer *) xmalloc (sizeof (struct buffer)); link->buf = buf; link->size = success; link->next = list; return link; } /* If we fail, see if we are at the mark. */ success = ioctl (socket, SIOCATMARK, &atmark); if (success < 0) perror ("ioctl"); if (atmark) { /* At the mark; skipping past more ordinary data cannot help. So just wait a while. */ sleep (1); continue; } /* Otherwise, read a bunch of ordinary data and save it. This is guaranteed not to read past the mark if it starts before the mark. */ success = read (socket, buf, BUF_SZ); if (success < 0) perror ("read"); /* Save this data in the buffer list. */ { struct buffer *link = (struct buffer *) xmalloc (sizeof (struct buffer)); link->buf = buf; link->size = success; /* Add the new link to the end of the list. */ if (tail) tail->next = link; else list = link; tail = link; } } }  File: libc.info, Node: Datagrams, Next: Inetd, Prev: Connections, Up: Sockets 16.10 Datagram Socket Operations ================================ This section describes how to use communication styles that don't use connections (styles ‘SOCK_DGRAM’ and ‘SOCK_RDM’). Using these styles, you group data into packets and each packet is an independent communication. You specify the destination for each packet individually. Datagram packets are like letters: you send each one independently with its own destination address, and they may arrive in the wrong order or not at all. The ‘listen’ and ‘accept’ functions are not allowed for sockets using connectionless communication styles. * Menu: * Sending Datagrams:: Sending packets on a datagram socket. * Receiving Datagrams:: Receiving packets on a datagram socket. * Datagram Example:: An example program: packets sent over a datagram socket in the local namespace. * Example Receiver:: Another program, that receives those packets.  File: libc.info, Node: Sending Datagrams, Next: Receiving Datagrams, Up: Datagrams 16.10.1 Sending Datagrams ------------------------- The normal way of sending data on a datagram socket is by using the ‘sendto’ function, declared in ‘sys/socket.h’. You can call ‘connect’ on a datagram socket, but this only specifies a default destination for further data transmission on the socket. When a socket has a default destination you can use ‘send’ (*note Sending Data::) or even ‘write’ (*note I/O Primitives::) to send a packet there. You can cancel the default destination by calling ‘connect’ using an address format of ‘AF_UNSPEC’ in the ADDR argument. *Note Connecting::, for more information about the ‘connect’ function. -- Function: ssize_t sendto (int SOCKET, const void *BUFFER, size_t SIZE, int FLAGS, struct sockaddr *ADDR, socklen_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘sendto’ function transmits the data in the BUFFER through the socket SOCKET to the destination address specified by the ADDR and LENGTH arguments. The SIZE argument specifies the number of bytes to be transmitted. The FLAGS are interpreted the same way as for ‘send’; see *note Socket Data Options::. The return value and error conditions are also the same as for ‘send’, but you cannot rely on the system to detect errors and report them; the most common error is that the packet is lost or there is no-one at the specified address to receive it, and the operating system on your machine usually does not know this. It is also possible for one call to ‘sendto’ to report an error owing to a problem related to a previous call. This function is defined as a cancellation point in multi-threaded programs, so one has to be prepared for this and make sure that allocated resources (like memory, file descriptors, semaphores or whatever) are freed even if the thread is canceled.  File: libc.info, Node: Receiving Datagrams, Next: Datagram Example, Prev: Sending Datagrams, Up: Datagrams 16.10.2 Receiving Datagrams --------------------------- The ‘recvfrom’ function reads a packet from a datagram socket and also tells you where it was sent from. This function is declared in ‘sys/socket.h’. -- Function: ssize_t recvfrom (int SOCKET, void *BUFFER, size_t SIZE, int FLAGS, struct sockaddr *ADDR, socklen_t *LENGTH-PTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘recvfrom’ function reads one packet from the socket SOCKET into the buffer BUFFER. The SIZE argument specifies the maximum number of bytes to be read. If the packet is longer than SIZE bytes, then you get the first SIZE bytes of the packet and the rest of the packet is lost. There's no way to read the rest of the packet. Thus, when you use a packet protocol, you must always know how long a packet to expect. The ADDR and LENGTH-PTR arguments are used to return the address where the packet came from. *Note Socket Addresses::. For a socket in the local domain the address information won't be meaningful, since you can't read the address of such a socket (*note Local Namespace::). You can specify a null pointer as the ADDR argument if you are not interested in this information. The FLAGS are interpreted the same way as for ‘recv’ (*note Socket Data Options::). The return value and error conditions are also the same as for ‘recv’. This function is defined as a cancellation point in multi-threaded programs, so one has to be prepared for this and make sure that allocated resources (like memory, file descriptors, semaphores or whatever) are freed even if the thread is canceled. You can use plain ‘recv’ (*note Receiving Data::) instead of ‘recvfrom’ if you don't need to find out who sent the packet (either because you know where it should come from or because you treat all possible senders alike). Even ‘read’ can be used if you don't want to specify FLAGS (*note I/O Primitives::). If you need more flexibility and/or control over sending and receiving packets, see ‘sendmsg’ and ‘recvmsg’ (*note Other Socket APIs::).  File: libc.info, Node: Datagram Example, Next: Example Receiver, Prev: Receiving Datagrams, Up: Datagrams 16.10.3 Datagram Socket Example ------------------------------- Here is a set of example programs that send messages over a datagram stream in the local namespace. Both the client and server programs use the ‘make_named_socket’ function that was presented in *note Local Socket Example::, to create and name their sockets. First, here is the server program. It sits in a loop waiting for messages to arrive, bouncing each message back to the sender. Obviously this isn't a particularly useful program, but it does show the general ideas involved. #include #include #include #include #include #define SERVER "/tmp/serversocket" #define MAXMSG 512 int main (void) { int sock; char message[MAXMSG]; struct sockaddr_un name; size_t size; int nbytes; /* Remove the filename first, it's ok if the call fails */ unlink (SERVER); /* Make the socket, then loop endlessly. */ sock = make_named_socket (SERVER); while (1) { /* Wait for a datagram. */ size = sizeof (name); nbytes = recvfrom (sock, message, MAXMSG, 0, (struct sockaddr *) & name, &size); if (nbytes < 0) { perror ("recfrom (server)"); exit (EXIT_FAILURE); } /* Give a diagnostic message. */ fprintf (stderr, "Server: got message: %s\n", message); /* Bounce the message back to the sender. */ nbytes = sendto (sock, message, nbytes, 0, (struct sockaddr *) & name, size); if (nbytes < 0) { perror ("sendto (server)"); exit (EXIT_FAILURE); } } }  File: libc.info, Node: Example Receiver, Prev: Datagram Example, Up: Datagrams 16.10.4 Example of Reading Datagrams ------------------------------------ Here is the client program corresponding to the server above. It sends a datagram to the server and then waits for a reply. Notice that the socket for the client (as well as for the server) in this example has to be given a name. This is so that the server can direct a message back to the client. Since the socket has no associated connection state, the only way the server can do this is by referencing the name of the client. #include #include #include #include #include #include #define SERVER "/tmp/serversocket" #define CLIENT "/tmp/mysocket" #define MAXMSG 512 #define MESSAGE "Yow!!! Are we having fun yet?!?" int main (void) { extern int make_named_socket (const char *name); int sock; char message[MAXMSG]; struct sockaddr_un name; size_t size; int nbytes; /* Make the socket. */ sock = make_named_socket (CLIENT); /* Initialize the server socket address. */ name.sun_family = AF_LOCAL; strcpy (name.sun_path, SERVER); size = strlen (name.sun_path) + sizeof (name.sun_family); /* Send the datagram. */ nbytes = sendto (sock, MESSAGE, strlen (MESSAGE) + 1, 0, (struct sockaddr *) & name, size); if (nbytes < 0) { perror ("sendto (client)"); exit (EXIT_FAILURE); } /* Wait for a reply. */ nbytes = recvfrom (sock, message, MAXMSG, 0, NULL, 0); if (nbytes < 0) { perror ("recfrom (client)"); exit (EXIT_FAILURE); } /* Print a diagnostic message. */ fprintf (stderr, "Client: got message: %s\n", message); /* Clean up. */ remove (CLIENT); close (sock); } Keep in mind that datagram socket communications are unreliable. In this example, the client program waits indefinitely if the message never reaches the server or if the server's response never comes back. It's up to the user running the program to kill and restart it if desired. A more automatic solution could be to use ‘select’ (*note Waiting for I/O::) to establish a timeout period for the reply, and in case of timeout either re-send the message or shut down the socket and exit.  File: libc.info, Node: Inetd, Next: Socket Options, Prev: Datagrams, Up: Sockets 16.11 The ‘inetd’ Daemon ======================== We've explained above how to write a server program that does its own listening. Such a server must already be running in order for anyone to connect to it. Another way to provide a service on an Internet port is to let the daemon program ‘inetd’ do the listening. ‘inetd’ is a program that runs all the time and waits (using ‘select’) for messages on a specified set of ports. When it receives a message, it accepts the connection (if the socket style calls for connections) and then forks a child process to run the corresponding server program. You specify the ports and their programs in the file ‘/etc/inetd.conf’. * Menu: * Inetd Servers:: * Configuring Inetd::  File: libc.info, Node: Inetd Servers, Next: Configuring Inetd, Up: Inetd 16.11.1 ‘inetd’ Servers ----------------------- Writing a server program to be run by ‘inetd’ is very simple. Each time someone requests a connection to the appropriate port, a new server process starts. The connection already exists at this time; the socket is available as the standard input descriptor and as the standard output descriptor (descriptors 0 and 1) in the server process. Thus the server program can begin reading and writing data right away. Often the program needs only the ordinary I/O facilities; in fact, a general-purpose filter program that knows nothing about sockets can work as a byte stream server run by ‘inetd’. You can also use ‘inetd’ for servers that use connectionless communication styles. For these servers, ‘inetd’ does not try to accept a connection since no connection is possible. It just starts the server program, which can read the incoming datagram packet from descriptor 0. The server program can handle one request and then exit, or you can choose to write it to keep reading more requests until no more arrive, and then exit. You must specify which of these two techniques the server uses when you configure ‘inetd’.  File: libc.info, Node: Configuring Inetd, Prev: Inetd Servers, Up: Inetd 16.11.2 Configuring ‘inetd’ --------------------------- The file ‘/etc/inetd.conf’ tells ‘inetd’ which ports to listen to and what server programs to run for them. Normally each entry in the file is one line, but you can split it onto multiple lines provided all but the first line of the entry start with whitespace. Lines that start with ‘#’ are comments. Here are two standard entries in ‘/etc/inetd.conf’: ftp stream tcp nowait root /libexec/ftpd ftpd talk dgram udp wait root /libexec/talkd talkd An entry has this format: SERVICE STYLE PROTOCOL WAIT USERNAME PROGRAM ARGUMENTS The SERVICE field says which service this program provides. It should be the name of a service defined in ‘/etc/services’. ‘inetd’ uses SERVICE to decide which port to listen on for this entry. The fields STYLE and PROTOCOL specify the communication style and the protocol to use for the listening socket. The style should be the name of a communication style, converted to lower case and with ‘SOCK_’ deleted--for example, ‘stream’ or ‘dgram’. PROTOCOL should be one of the protocols listed in ‘/etc/protocols’. The typical protocol names are ‘tcp’ for byte stream connections and ‘udp’ for unreliable datagrams. The WAIT field should be either ‘wait’ or ‘nowait’. Use ‘wait’ if STYLE is a connectionless style and the server, once started, handles multiple requests as they come in. Use ‘nowait’ if ‘inetd’ should start a new process for each message or request that comes in. If STYLE uses connections, then WAIT *must* be ‘nowait’. USER is the user name that the server should run as. ‘inetd’ runs as root, so it can set the user ID of its children arbitrarily. It's best to avoid using ‘root’ for USER if you can; but some servers, such as Telnet and FTP, read a username and passphrase themselves. These servers need to be root initially so they can log in as commanded by the data coming over the network. PROGRAM together with ARGUMENTS specifies the command to run to start the server. PROGRAM should be an absolute file name specifying the executable file to run. ARGUMENTS consists of any number of whitespace-separated words, which become the command-line arguments of PROGRAM. The first word in ARGUMENTS is argument zero, which should by convention be the program name itself (sans directories). If you edit ‘/etc/inetd.conf’, you can tell ‘inetd’ to reread the file and obey its new contents by sending the ‘inetd’ process the ‘SIGHUP’ signal. You'll have to use ‘ps’ to determine the process ID of the ‘inetd’ process as it is not fixed.  File: libc.info, Node: Socket Options, Next: Networks Database, Prev: Inetd, Up: Sockets 16.12 Socket Options ==================== This section describes how to read or set various options that modify the behavior of sockets and their underlying communications protocols. When you are manipulating a socket option, you must specify which “level” the option pertains to. This describes whether the option applies to the socket interface, or to a lower-level communications protocol interface. * Menu: * Socket Option Functions:: The basic functions for setting and getting socket options. * Socket-Level Options:: Details of the options at the socket level.  File: libc.info, Node: Socket Option Functions, Next: Socket-Level Options, Up: Socket Options 16.12.1 Socket Option Functions ------------------------------- Here are the functions for examining and modifying socket options. They are declared in ‘sys/socket.h’. -- Function: int getsockopt (int SOCKET, int LEVEL, int OPTNAME, void *OPTVAL, socklen_t *OPTLEN-PTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘getsockopt’ function gets information about the value of option OPTNAME at level LEVEL for socket SOCKET. The option value is stored in the buffer that OPTVAL points to. Before the call, you should supply in ‘*OPTLEN-PTR’ the size of this buffer; on return, it contains the number of bytes of information actually stored in the buffer. Most options interpret the OPTVAL buffer as a single ‘int’ value. The actual return value of ‘getsockopt’ is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined: ‘EBADF’ The SOCKET argument is not a valid file descriptor. ‘ENOTSOCK’ The descriptor SOCKET is not a socket. ‘ENOPROTOOPT’ The OPTNAME doesn't make sense for the given LEVEL. -- Function: int setsockopt (int SOCKET, int LEVEL, int OPTNAME, const void *OPTVAL, socklen_t OPTLEN) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is used to set the socket option OPTNAME at level LEVEL for socket SOCKET. The value of the option is passed in the buffer OPTVAL of size OPTLEN. The return value and error codes for ‘setsockopt’ are the same as for ‘getsockopt’.  File: libc.info, Node: Socket-Level Options, Prev: Socket Option Functions, Up: Socket Options 16.12.2 Socket-Level Options ---------------------------- -- Constant: int SOL_SOCKET Use this constant as the LEVEL argument to ‘getsockopt’ or ‘setsockopt’ to manipulate the socket-level options described in this section. Here is a table of socket-level option names; all are defined in the header file ‘sys/socket.h’. ‘SO_DEBUG’ This option toggles recording of debugging information in the underlying protocol modules. The value has type ‘int’; a nonzero value means "yes". ‘SO_REUSEADDR’ This option controls whether ‘bind’ (*note Setting Address::) should permit reuse of local addresses for this socket. If you enable this option, you can actually have two sockets with the same Internet port number; but the system won't allow you to use the two identically-named sockets in a way that would confuse the Internet. The reason for this option is that some higher-level Internet protocols, including FTP, require you to keep reusing the same port number. The value has type ‘int’; a nonzero value means "yes". ‘SO_KEEPALIVE’ This option controls whether the underlying protocol should periodically transmit messages on a connected socket. If the peer fails to respond to these messages, the connection is considered broken. The value has type ‘int’; a nonzero value means "yes". ‘SO_DONTROUTE’ This option controls whether outgoing messages bypass the normal message routing facilities. If set, messages are sent directly to the network interface instead. The value has type ‘int’; a nonzero value means "yes". ‘SO_LINGER’ This option specifies what should happen when the socket of a type that promises reliable delivery still has untransmitted messages when it is closed; see *note Closing a Socket::. The value has type ‘struct linger’. -- Data Type: struct linger This structure type has the following members: ‘int l_onoff’ This field is interpreted as a boolean. If nonzero, ‘close’ blocks until the data are transmitted or the timeout period has expired. ‘int l_linger’ This specifies the timeout period, in seconds. ‘SO_BROADCAST’ This option controls whether datagrams may be broadcast from the socket. The value has type ‘int’; a nonzero value means "yes". ‘SO_OOBINLINE’ If this option is set, out-of-band data received on the socket is placed in the normal input queue. This permits it to be read using ‘read’ or ‘recv’ without specifying the ‘MSG_OOB’ flag. *Note Out-of-Band Data::. The value has type ‘int’; a nonzero value means "yes". ‘SO_SNDBUF’ This option gets or sets the size of the output buffer. The value is a ‘size_t’, which is the size in bytes. ‘SO_RCVBUF’ This option gets or sets the size of the input buffer. The value is a ‘size_t’, which is the size in bytes. ‘SO_STYLE’ ‘SO_TYPE’ This option can be used with ‘getsockopt’ only. It is used to get the socket's communication style. ‘SO_TYPE’ is the historical name, and ‘SO_STYLE’ is the preferred name in GNU. The value has type ‘int’ and its value designates a communication style; see *note Communication Styles::. ‘SO_ERROR’ This option can be used with ‘getsockopt’ only. It is used to reset the error status of the socket. The value is an ‘int’, which represents the previous error status.  File: libc.info, Node: Networks Database, Next: Other Socket APIs, Prev: Socket Options, Up: Sockets 16.13 Networks Database ======================= Many systems come with a database that records a list of networks known to the system developer. This is usually kept either in the file ‘/etc/networks’ or in an equivalent from a name server. This data base is useful for routing programs such as ‘route’, but it is not useful for programs that simply communicate over the network. We provide functions to access this database, which are declared in ‘netdb.h’. -- Data Type: struct netent This data type is used to represent information about entries in the networks database. It has the following members: ‘char *n_name’ This is the "official" name of the network. ‘char **n_aliases’ These are alternative names for the network, represented as a vector of strings. A null pointer terminates the array. ‘int n_addrtype’ This is the type of the network number; this is always equal to ‘AF_INET’ for Internet networks. ‘unsigned long int n_net’ This is the network number. Network numbers are returned in host byte order; see *note Byte Order::. Use the ‘getnetbyname’ or ‘getnetbyaddr’ functions to search the networks database for information about a specific network. The information is returned in a statically-allocated structure; you must copy the information if you need to save it. -- Function: struct netent * getnetbyname (const char *NAME) Preliminary: | MT-Unsafe race:netbyname env locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘getnetbyname’ function returns information about the network named NAME. It returns a null pointer if there is no such network. -- Function: struct netent * getnetbyaddr (uint32_t NET, int TYPE) Preliminary: | MT-Unsafe race:netbyaddr locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘getnetbyaddr’ function returns information about the network of type TYPE with number NET. You should specify a value of ‘AF_INET’ for the TYPE argument for Internet networks. ‘getnetbyaddr’ returns a null pointer if there is no such network. You can also scan the networks database using ‘setnetent’, ‘getnetent’ and ‘endnetent’. Be careful when using these functions because they are not reentrant. -- Function: void setnetent (int STAYOPEN) Preliminary: | MT-Unsafe race:netent env locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function opens and rewinds the networks database. If the STAYOPEN argument is nonzero, this sets a flag so that subsequent calls to ‘getnetbyname’ or ‘getnetbyaddr’ will not close the database (as they usually would). This makes for more efficiency if you call those functions several times, by avoiding reopening the database for each call. -- Function: struct netent * getnetent (void) Preliminary: | MT-Unsafe race:netent race:netentbuf env locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function returns the next entry in the networks database. It returns a null pointer if there are no more entries. -- Function: void endnetent (void) Preliminary: | MT-Unsafe race:netent env locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function closes the networks database.  File: libc.info, Node: Other Socket APIs, Prev: Networks Database, Up: Sockets 16.14 Other Socket APIs ======================= -- Data Type: struct msghdr -- Function: ssize_t sendmsg (int SOCKET, const struct msghdr *MESSAGE, int FLAGS) This documentation is a stub. For additional information on this function, consult the manual page . *Note Linux Kernel::. -- Function: ssize_t recvmsg (int SOCKET, struct msghdr *MESSAGE, int FLAGS) This documentation is a stub. For additional information on this function, consult the manual page . *Note Linux Kernel::.  File: libc.info, Node: Low-Level Terminal Interface, Next: Syslog, Prev: Sockets, Up: Top 17 Low-Level Terminal Interface ******************************* This chapter describes functions that are specific to terminal devices. You can use these functions to do things like turn off input echoing; set serial line characteristics such as line speed and flow control; and change which characters are used for end-of-file, command-line editing, sending signals, and similar control functions. Most of the functions in this chapter operate on file descriptors. *Note Low-Level I/O::, for more information about what a file descriptor is and how to open a file descriptor for a terminal device. * Menu: * Is It a Terminal:: How to determine if a file is a terminal device, and what its name is. * I/O Queues:: About flow control and typeahead. * Canonical or Not:: Two basic styles of input processing. * Terminal Modes:: How to examine and modify flags controlling details of terminal I/O: echoing, signals, editing. Posix. * BSD Terminal Modes:: BSD compatible terminal mode setting * Line Control:: Sending break sequences, clearing terminal buffers ... * Noncanon Example:: How to read single characters without echo. * getpass:: Prompting the user for a passphrase. * Pseudo-Terminals:: How to open a pseudo-terminal.  File: libc.info, Node: Is It a Terminal, Next: I/O Queues, Up: Low-Level Terminal Interface 17.1 Identifying Terminals ========================== The functions described in this chapter only work on files that correspond to terminal devices. You can find out whether a file descriptor is associated with a terminal by using the ‘isatty’ function. Prototypes for the functions in this section are declared in the header file ‘unistd.h’. -- Function: int isatty (int FILEDES) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns ‘1’ if FILEDES is a file descriptor associated with an open terminal device, and 0 otherwise. If a file descriptor is associated with a terminal, you can get its associated file name using the ‘ttyname’ function. See also the ‘ctermid’ function, described in *note Identifying the Terminal::. -- Function: char * ttyname (int FILEDES) Preliminary: | MT-Unsafe race:ttyname | AS-Unsafe heap lock | AC-Unsafe lock fd mem | *Note POSIX Safety Concepts::. If the file descriptor FILEDES is associated with a terminal device, the ‘ttyname’ function returns a pointer to a statically-allocated, null-terminated string containing the file name of the terminal file. The value is a null pointer if the file descriptor isn't associated with a terminal, or the file name cannot be determined. -- Function: int ttyname_r (int FILEDES, char *BUF, size_t LEN) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘ttyname_r’ function is similar to the ‘ttyname’ function except that it places its result into the user-specified buffer starting at BUF with length LEN. The normal return value from ‘ttyname_r’ is 0. Otherwise an error number is returned to indicate the error. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘ENOTTY’ The FILEDES is not associated with a terminal. ‘ERANGE’ The buffer length LEN is too small to store the string to be returned. ‘ENODEV’ The FILEDES is associated with a terminal device that is a slave pseudo-terminal, but the file name associated with that device could not be determined. This is a GNU extension.  File: libc.info, Node: I/O Queues, Next: Canonical or Not, Prev: Is It a Terminal, Up: Low-Level Terminal Interface 17.2 I/O Queues =============== Many of the remaining functions in this section refer to the input and output queues of a terminal device. These queues implement a form of buffering _within the kernel_ independent of the buffering implemented by I/O streams (*note I/O on Streams::). The “terminal input queue” is also sometimes referred to as its “typeahead buffer”. It holds the characters that have been received from the terminal but not yet read by any process. The size of the input queue is described by the ‘MAX_INPUT’ and ‘_POSIX_MAX_INPUT’ parameters; see *note Limits for Files::. You are guaranteed a queue size of at least ‘MAX_INPUT’, but the queue might be larger, and might even dynamically change size. If input flow control is enabled by setting the ‘IXOFF’ input mode bit (*note Input Modes::), the terminal driver transmits STOP and START characters to the terminal when necessary to prevent the queue from overflowing. Otherwise, input may be lost if it comes in too fast from the terminal. In canonical mode, all input stays in the queue until a newline character is received, so the terminal input queue can fill up when you type a very long line. *Note Canonical or Not::. The “terminal output queue” is like the input queue, but for output; it contains characters that have been written by processes, but not yet transmitted to the terminal. If output flow control is enabled by setting the ‘IXON’ input mode bit (*note Input Modes::), the terminal driver obeys START and STOP characters sent by the terminal to stop and restart transmission of output. “Clearing” the terminal input queue means discarding any characters that have been received but not yet read. Similarly, clearing the terminal output queue means discarding any characters that have been written but not yet transmitted.  File: libc.info, Node: Canonical or Not, Next: Terminal Modes, Prev: I/O Queues, Up: Low-Level Terminal Interface 17.3 Two Styles of Input: Canonical or Not ========================================== POSIX systems support two basic modes of input: canonical and noncanonical. In “canonical input processing” mode, terminal input is processed in lines terminated by newline (‘'\n'’), EOF, or EOL characters. No input can be read until an entire line has been typed by the user, and the ‘read’ function (*note I/O Primitives::) returns at most a single line of input, no matter how many bytes are requested. In canonical input mode, the operating system provides input editing facilities: some characters are interpreted specially to perform editing operations within the current line of text, such as ERASE and KILL. *Note Editing Characters::. The constants ‘_POSIX_MAX_CANON’ and ‘MAX_CANON’ parameterize the maximum number of bytes which may appear in a single line of canonical input. *Note Limits for Files::. You are guaranteed a maximum line length of at least ‘MAX_CANON’ bytes, but the maximum might be larger, and might even dynamically change size. In “noncanonical input processing” mode, characters are not grouped into lines, and ERASE and KILL processing is not performed. The granularity with which bytes are read in noncanonical input mode is controlled by the MIN and TIME settings. *Note Noncanonical Input::. Most programs use canonical input mode, because this gives the user a way to edit input line by line. The usual reason to use noncanonical mode is when the program accepts single-character commands or provides its own editing facilities. The choice of canonical or noncanonical input is controlled by the ‘ICANON’ flag in the ‘c_lflag’ member of ‘struct termios’. *Note Local Modes::.  File: libc.info, Node: Terminal Modes, Next: BSD Terminal Modes, Prev: Canonical or Not, Up: Low-Level Terminal Interface 17.4 Terminal Modes =================== This section describes the various terminal attributes that control how input and output are done. The functions, data structures, and symbolic constants are all declared in the header file ‘termios.h’. Don't confuse terminal attributes with file attributes. A device special file which is associated with a terminal has file attributes as described in *note File Attributes::. These are unrelated to the attributes of the terminal device itself, which are discussed in this section. * Menu: * Mode Data Types:: The data type ‘struct termios’ and related types. * Mode Functions:: Functions to read and set the terminal attributes. * Setting Modes:: The right way to set terminal attributes reliably. * Input Modes:: Flags controlling low-level input handling. * Output Modes:: Flags controlling low-level output handling. * Control Modes:: Flags controlling serial port behavior. * Local Modes:: Flags controlling high-level input handling. * Line Speed:: How to read and set the terminal line speed. * Special Characters:: Characters that have special effects, and how to change them. * Noncanonical Input:: Controlling how long to wait for input.  File: libc.info, Node: Mode Data Types, Next: Mode Functions, Up: Terminal Modes 17.4.1 Terminal Mode Data Types ------------------------------- The entire collection of attributes of a terminal is stored in a structure of type ‘struct termios’. This structure is used with the functions ‘tcgetattr’ and ‘tcsetattr’ to read and set the attributes. -- Data Type: struct termios A ‘struct termios’ records all the I/O attributes of a terminal. The structure includes at least the following members: ‘tcflag_t c_iflag’ A bit mask specifying flags for input modes; see *note Input Modes::. ‘tcflag_t c_oflag’ A bit mask specifying flags for output modes; see *note Output Modes::. ‘tcflag_t c_cflag’ A bit mask specifying flags for control modes; see *note Control Modes::. ‘tcflag_t c_lflag’ A bit mask specifying flags for local modes; see *note Local Modes::. ‘cc_t c_cc[NCCS]’ An array specifying which characters are associated with various control functions; see *note Special Characters::. The ‘struct termios’ structure also contains members which encode input and output transmission speeds, but the representation is not specified. *Note Line Speed::, for how to examine and store the speed values. The following sections describe the details of the members of the ‘struct termios’ structure. -- Data Type: tcflag_t This is an unsigned integer type used to represent the various bit masks for terminal flags. -- Data Type: cc_t This is an unsigned integer type used to represent characters associated with various terminal control functions. -- Macro: int NCCS The value of this macro is the number of elements in the ‘c_cc’ array.  File: libc.info, Node: Mode Functions, Next: Setting Modes, Prev: Mode Data Types, Up: Terminal Modes 17.4.2 Terminal Mode Functions ------------------------------ -- Function: int tcgetattr (int FILEDES, struct termios *TERMIOS-P) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is used to examine the attributes of the terminal device with file descriptor FILEDES. The attributes are returned in the structure that TERMIOS-P points to. If successful, ‘tcgetattr’ returns 0. A return value of -1 indicates an error. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘ENOTTY’ The FILEDES is not associated with a terminal. -- Function: int tcsetattr (int FILEDES, int WHEN, const struct termios *TERMIOS-P) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function sets the attributes of the terminal device with file descriptor FILEDES. The new attributes are taken from the structure that TERMIOS-P points to. The WHEN argument specifies how to deal with input and output already queued. It can be one of the following values: ‘TCSANOW’ Make the change immediately. ‘TCSADRAIN’ Make the change after waiting until all queued output has been written. You should usually use this option when changing parameters that affect output. ‘TCSAFLUSH’ This is like ‘TCSADRAIN’, but also discards any queued input. ‘TCSASOFT’ This is a flag bit that you can add to any of the above alternatives. Its meaning is to inhibit alteration of the state of the terminal hardware. It is a BSD extension; it is only supported on BSD systems and GNU/Hurd systems. Using ‘TCSASOFT’ is exactly the same as setting the ‘CIGNORE’ bit in the ‘c_cflag’ member of the structure TERMIOS-P points to. *Note Control Modes::, for a description of ‘CIGNORE’. If this function is called from a background process on its controlling terminal, normally all processes in the process group are sent a ‘SIGTTOU’ signal, in the same way as if the process were trying to write to the terminal. The exception is if the calling process itself is ignoring or blocking ‘SIGTTOU’ signals, in which case the operation is performed and no signal is sent. *Note Job Control::. If successful, ‘tcsetattr’ returns 0. A return value of -1 indicates an error. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘ENOTTY’ The FILEDES is not associated with a terminal. ‘EINVAL’ Either the value of the ‘when’ argument is not valid, or there is something wrong with the data in the TERMIOS-P argument. Although ‘tcgetattr’ and ‘tcsetattr’ specify the terminal device with a file descriptor, the attributes are those of the terminal device itself and not of the file descriptor. This means that the effects of changing terminal attributes are persistent; if another process opens the terminal file later on, it will see the changed attributes even though it doesn't have anything to do with the open file descriptor you originally specified in changing the attributes. Similarly, if a single process has multiple or duplicated file descriptors for the same terminal device, changing the terminal attributes affects input and output to all of these file descriptors. This means, for example, that you can't open one file descriptor or stream to read from a terminal in the normal line-buffered, echoed mode; and simultaneously have another file descriptor for the same terminal that you use to read from it in single-character, non-echoed mode. Instead, you have to explicitly switch the terminal back and forth between the two modes.  File: libc.info, Node: Setting Modes, Next: Input Modes, Prev: Mode Functions, Up: Terminal Modes 17.4.3 Setting Terminal Modes Properly -------------------------------------- When you set terminal modes, you should call ‘tcgetattr’ first to get the current modes of the particular terminal device, modify only those modes that you are really interested in, and store the result with ‘tcsetattr’. It's a bad idea to simply initialize a ‘struct termios’ structure to a chosen set of attributes and pass it directly to ‘tcsetattr’. Your program may be run years from now, on systems that support members not documented in this manual. The way to avoid setting these members to unreasonable values is to avoid changing them. What's more, different terminal devices may require different mode settings in order to function properly. So you should avoid blindly copying attributes from one terminal device to another. When a member contains a collection of independent flags, as the ‘c_iflag’, ‘c_oflag’ and ‘c_cflag’ members do, even setting the entire member is a bad idea, because particular operating systems have their own flags. Instead, you should start with the current value of the member and alter only the flags whose values matter in your program, leaving any other flags unchanged. Here is an example of how to set one flag (‘ISTRIP’) in the ‘struct termios’ structure while properly preserving all the other data in the structure: int set_istrip (int desc, int value) { struct termios settings; int result; result = tcgetattr (desc, &settings); if (result < 0) { perror ("error in tcgetattr"); return 0; } settings.c_iflag &= ~ISTRIP; if (value) settings.c_iflag |= ISTRIP; result = tcsetattr (desc, TCSANOW, &settings); if (result < 0) { perror ("error in tcsetattr"); return 0; } return 1; }  File: libc.info, Node: Input Modes, Next: Output Modes, Prev: Setting Modes, Up: Terminal Modes 17.4.4 Input Modes ------------------ This section describes the terminal attribute flags that control fairly low-level aspects of input processing: handling of parity errors, break signals, flow control, and and characters. All of these flags are bits in the ‘c_iflag’ member of the ‘struct termios’ structure. The member is an integer, and you change flags using the operators ‘&’, ‘|’ and ‘^’. Don't try to specify the entire value for ‘c_iflag’--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). -- Macro: tcflag_t INPCK If this bit is set, input parity checking is enabled. If it is not set, no checking at all is done for parity errors on input; the characters are simply passed through to the application. Parity checking on input processing is independent of whether parity detection and generation on the underlying terminal hardware is enabled; see *note Control Modes::. For example, you could clear the ‘INPCK’ input mode flag and set the ‘PARENB’ control mode flag to ignore parity errors on input, but still generate parity on output. If this bit is set, what happens when a parity error is detected depends on whether the ‘IGNPAR’ or ‘PARMRK’ bits are set. If neither of these bits are set, a byte with a parity error is passed to the application as a ‘'\0'’ character. -- Macro: tcflag_t IGNPAR If this bit is set, any byte with a framing or parity error is ignored. This is only useful if ‘INPCK’ is also set. -- Macro: tcflag_t PARMRK If this bit is set, input bytes with parity or framing errors are marked when passed to the program. This bit is meaningful only when ‘INPCK’ is set and ‘IGNPAR’ is not set. The way erroneous bytes are marked is with two preceding bytes, ‘377’ and ‘0’. Thus, the program actually reads three bytes for one erroneous byte received from the terminal. If a valid byte has the value ‘0377’, and ‘ISTRIP’ (see below) is not set, the program might confuse it with the prefix that marks a parity error. So a valid byte ‘0377’ is passed to the program as two bytes, ‘0377’ ‘0377’, in this case. -- Macro: tcflag_t ISTRIP If this bit is set, valid input bytes are stripped to seven bits; otherwise, all eight bits are available for programs to read. -- Macro: tcflag_t IGNBRK If this bit is set, break conditions are ignored. A “break condition” is defined in the context of asynchronous serial data transmission as a series of zero-value bits longer than a single byte. -- Macro: tcflag_t BRKINT If this bit is set and ‘IGNBRK’ is not set, a break condition clears the terminal input and output queues and raises a ‘SIGINT’ signal for the foreground process group associated with the terminal. If neither ‘BRKINT’ nor ‘IGNBRK’ are set, a break condition is passed to the application as a single ‘'\0'’ character if ‘PARMRK’ is not set, or otherwise as a three-character sequence ‘'\377'’, ‘'\0'’, ‘'\0'’. -- Macro: tcflag_t IGNCR If this bit is set, carriage return characters (‘'\r'’) are discarded on input. Discarding carriage return may be useful on terminals that send both carriage return and linefeed when you type the key. -- Macro: tcflag_t ICRNL If this bit is set and ‘IGNCR’ is not set, carriage return characters (‘'\r'’) received as input are passed to the application as newline characters (‘'\n'’). -- Macro: tcflag_t INLCR If this bit is set, newline characters (‘'\n'’) received as input are passed to the application as carriage return characters (‘'\r'’). -- Macro: tcflag_t IXOFF If this bit is set, start/stop control on input is enabled. In other words, the computer sends STOP and START characters as necessary to prevent input from coming in faster than programs are reading it. The idea is that the actual terminal hardware that is generating the input data responds to a STOP character by suspending transmission, and to a START character by resuming transmission. *Note Start/Stop Characters::. -- Macro: tcflag_t IXON If this bit is set, start/stop control on output is enabled. In other words, if the computer receives a STOP character, it suspends output until a START character is received. In this case, the STOP and START characters are never passed to the application program. If this bit is not set, then START and STOP can be read as ordinary characters. *Note Start/Stop Characters::. -- Macro: tcflag_t IXANY If this bit is set, any input character restarts output when output has been suspended with the STOP character. Otherwise, only the START character restarts output. This is a BSD extension; it exists only on BSD systems and GNU/Linux and GNU/Hurd systems. -- Macro: tcflag_t IMAXBEL If this bit is set, then filling up the terminal input buffer sends a BEL character (code ‘007’) to the terminal to ring the bell. This is a BSD extension.  File: libc.info, Node: Output Modes, Next: Control Modes, Prev: Input Modes, Up: Terminal Modes 17.4.5 Output Modes ------------------- This section describes the terminal flags and fields that control how output characters are translated and padded for display. All of these are contained in the ‘c_oflag’ member of the ‘struct termios’ structure. The ‘c_oflag’ member itself is an integer, and you change the flags and fields using the operators ‘&’, ‘|’, and ‘^’. Don't try to specify the entire value for ‘c_oflag’--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). -- Macro: tcflag_t OPOST If this bit is set, output data is processed in some unspecified way so that it is displayed appropriately on the terminal device. This typically includes mapping newline characters (‘'\n'’) onto carriage return and linefeed pairs. If this bit isn't set, the characters are transmitted as-is. The following three bits are effective only if ‘OPOST’ is set. -- Macro: tcflag_t ONLCR If this bit is set, convert the newline character on output into a pair of characters, carriage return followed by linefeed. -- Macro: tcflag_t OXTABS If this bit is set, convert tab characters on output into the appropriate number of spaces to emulate a tab stop every eight columns. This bit exists only on BSD systems and GNU/Hurd systems; on GNU/Linux systems it is available as ‘XTABS’. -- Macro: tcflag_t ONOEOT If this bit is set, discard ‘C-d’ characters (code ‘004’) on output. These characters cause many dial-up terminals to disconnect. This bit exists only on BSD systems and GNU/Hurd systems.  File: libc.info, Node: Control Modes, Next: Local Modes, Prev: Output Modes, Up: Terminal Modes 17.4.6 Control Modes -------------------- This section describes the terminal flags and fields that control parameters usually associated with asynchronous serial data transmission. These flags may not make sense for other kinds of terminal ports (such as a network connection pseudo-terminal). All of these are contained in the ‘c_cflag’ member of the ‘struct termios’ structure. The ‘c_cflag’ member itself is an integer, and you change the flags and fields using the operators ‘&’, ‘|’, and ‘^’. Don't try to specify the entire value for ‘c_cflag’--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). -- Macro: tcflag_t CLOCAL If this bit is set, it indicates that the terminal is connected "locally" and that the modem status lines (such as carrier detect) should be ignored. On many systems if this bit is not set and you call ‘open’ without the ‘O_NONBLOCK’ flag set, ‘open’ blocks until a modem connection is established. If this bit is not set and a modem disconnect is detected, a ‘SIGHUP’ signal is sent to the controlling process group for the terminal (if it has one). Normally, this causes the process to exit; see *note Signal Handling::. Reading from the terminal after a disconnect causes an end-of-file condition, and writing causes an ‘EIO’ error to be returned. The terminal device must be closed and reopened to clear the condition. -- Macro: tcflag_t HUPCL If this bit is set, a modem disconnect is generated when all processes that have the terminal device open have either closed the file or exited. -- Macro: tcflag_t CREAD If this bit is set, input can be read from the terminal. Otherwise, input is discarded when it arrives. -- Macro: tcflag_t CSTOPB If this bit is set, two stop bits are used. Otherwise, only one stop bit is used. -- Macro: tcflag_t PARENB If this bit is set, generation and detection of a parity bit are enabled. *Note Input Modes::, for information on how input parity errors are handled. If this bit is not set, no parity bit is added to output characters, and input characters are not checked for correct parity. -- Macro: tcflag_t PARODD This bit is only useful if ‘PARENB’ is set. If ‘PARODD’ is set, odd parity is used, otherwise even parity is used. The control mode flags also includes a field for the number of bits per character. You can use the ‘CSIZE’ macro as a mask to extract the value, like this: ‘settings.c_cflag & CSIZE’. -- Macro: tcflag_t CSIZE This is a mask for the number of bits per character. -- Macro: tcflag_t CS5 This specifies five bits per byte. -- Macro: tcflag_t CS6 This specifies six bits per byte. -- Macro: tcflag_t CS7 This specifies seven bits per byte. -- Macro: tcflag_t CS8 This specifies eight bits per byte. The following four bits are BSD extensions; these exist only on BSD systems and GNU/Hurd systems. -- Macro: tcflag_t CCTS_OFLOW If this bit is set, enable flow control of output based on the CTS wire (RS232 protocol). -- Macro: tcflag_t CRTS_IFLOW If this bit is set, enable flow control of input based on the RTS wire (RS232 protocol). -- Macro: tcflag_t MDMBUF If this bit is set, enable carrier-based flow control of output. -- Macro: tcflag_t CIGNORE If this bit is set, it says to ignore the control modes and line speed values entirely. This is only meaningful in a call to ‘tcsetattr’. The ‘c_cflag’ member and the line speed values returned by ‘cfgetispeed’ and ‘cfgetospeed’ will be unaffected by the call. ‘CIGNORE’ is useful if you want to set all the software modes in the other members, but leave the hardware details in ‘c_cflag’ unchanged. (This is how the ‘TCSASOFT’ flag to ‘tcsettattr’ works.) This bit is never set in the structure filled in by ‘tcgetattr’.  File: libc.info, Node: Local Modes, Next: Line Speed, Prev: Control Modes, Up: Terminal Modes 17.4.7 Local Modes ------------------ This section describes the flags for the ‘c_lflag’ member of the ‘struct termios’ structure. These flags generally control higher-level aspects of input processing than the input modes flags described in *note Input Modes::, such as echoing, signals, and the choice of canonical or noncanonical input. The ‘c_lflag’ member itself is an integer, and you change the flags and fields using the operators ‘&’, ‘|’, and ‘^’. Don't try to specify the entire value for ‘c_lflag’--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). -- Macro: tcflag_t ICANON This bit, if set, enables canonical input processing mode. Otherwise, input is processed in noncanonical mode. *Note Canonical or Not::. -- Macro: tcflag_t ECHO If this bit is set, echoing of input characters back to the terminal is enabled. -- Macro: tcflag_t ECHOE If this bit is set, echoing indicates erasure of input with the ERASE character by erasing the last character in the current line from the screen. Otherwise, the character erased is re-echoed to show what has happened (suitable for a printing terminal). This bit only controls the display behavior; the ‘ICANON’ bit by itself controls actual recognition of the ERASE character and erasure of input, without which ‘ECHOE’ is simply irrelevant. -- Macro: tcflag_t ECHOPRT This bit, like ‘ECHOE’, enables display of the ERASE character in a way that is geared to a hardcopy terminal. When you type the ERASE character, a ‘\’ character is printed followed by the first character erased. Typing the ERASE character again just prints the next character erased. Then, the next time you type a normal character, a ‘/’ character is printed before the character echoes. This is a BSD extension, and exists only in BSD systems and GNU/Linux and GNU/Hurd systems. -- Macro: tcflag_t ECHOK This bit enables special display of the KILL character by moving to a new line after echoing the KILL character normally. The behavior of ‘ECHOKE’ (below) is nicer to look at. If this bit is not set, the KILL character echoes just as it would if it were not the KILL character. Then it is up to the user to remember that the KILL character has erased the preceding input; there is no indication of this on the screen. This bit only controls the display behavior; the ‘ICANON’ bit by itself controls actual recognition of the KILL character and erasure of input, without which ‘ECHOK’ is simply irrelevant. -- Macro: tcflag_t ECHOKE This bit is similar to ‘ECHOK’. It enables special display of the KILL character by erasing on the screen the entire line that has been killed. This is a BSD extension, and exists only in BSD systems and GNU/Linux and GNU/Hurd systems. -- Macro: tcflag_t ECHONL If this bit is set and the ‘ICANON’ bit is also set, then the newline (‘'\n'’) character is echoed even if the ‘ECHO’ bit is not set. -- Macro: tcflag_t ECHOCTL If this bit is set and the ‘ECHO’ bit is also set, echo control characters with ‘^’ followed by the corresponding text character. Thus, control-A echoes as ‘^A’. This is usually the preferred mode for interactive input, because echoing a control character back to the terminal could have some undesired effect on the terminal. This is a BSD extension, and exists only in BSD systems and GNU/Linux and GNU/Hurd systems. -- Macro: tcflag_t ISIG This bit controls whether the INTR, QUIT, and SUSP characters are recognized. The functions associated with these characters are performed if and only if this bit is set. Being in canonical or noncanonical input mode has no effect on the interpretation of these characters. You should use caution when disabling recognition of these characters. Programs that cannot be interrupted interactively are very user-unfriendly. If you clear this bit, your program should provide some alternate interface that allows the user to interactively send the signals associated with these characters, or to escape from the program. *Note Signal Characters::. -- Macro: tcflag_t IEXTEN POSIX.1 gives ‘IEXTEN’ implementation-defined meaning, so you cannot rely on this interpretation on all systems. On BSD systems and GNU/Linux and GNU/Hurd systems, it enables the LNEXT and DISCARD characters. *Note Other Special::. -- Macro: tcflag_t NOFLSH Normally, the INTR, QUIT, and SUSP characters cause input and output queues for the terminal to be cleared. If this bit is set, the queues are not cleared. -- Macro: tcflag_t TOSTOP If this bit is set and the system supports job control, then ‘SIGTTOU’ signals are generated by background processes that attempt to write to the terminal. *Note Access to the Terminal::. The following bits are BSD extensions; they exist only on BSD systems and GNU/Hurd systems. -- Macro: tcflag_t ALTWERASE This bit determines how far the WERASE character should erase. The WERASE character erases back to the beginning of a word; the question is, where do words begin? If this bit is clear, then the beginning of a word is a nonwhitespace character following a whitespace character. If the bit is set, then the beginning of a word is an alphanumeric character or underscore following a character which is none of those. *Note Editing Characters::, for more information about the WERASE character. -- Macro: tcflag_t FLUSHO This is the bit that toggles when the user types the DISCARD character. While this bit is set, all output is discarded. *Note Other Special::. -- Macro: tcflag_t NOKERNINFO Setting this bit disables handling of the STATUS character. *Note Other Special::. -- Macro: tcflag_t PENDIN If this bit is set, it indicates that there is a line of input that needs to be reprinted. Typing the REPRINT character sets this bit; the bit remains set until reprinting is finished. *Note Editing Characters::.  File: libc.info, Node: Line Speed, Next: Special Characters, Prev: Local Modes, Up: Terminal Modes 17.4.8 Line Speed ----------------- The terminal line speed tells the computer how fast to read and write data on the terminal. If the terminal is connected to a real serial line, the terminal speed you specify actually controls the line--if it doesn't match the terminal's own idea of the speed, communication does not work. Real serial ports accept only certain standard speeds. Also, particular hardware may not support even all the standard speeds. Specifying a speed of zero hangs up a dialup connection and turns off modem control signals. If the terminal is not a real serial line (for example, if it is a network connection), then the line speed won't really affect data transmission speed, but some programs will use it to determine the amount of padding needed. It's best to specify a line speed value that matches the actual speed of the actual terminal, but you can safely experiment with different values to vary the amount of padding. There are actually two line speeds for each terminal, one for input and one for output. You can set them independently, but most often terminals use the same speed for both directions. The speed values are stored in the ‘struct termios’ structure, but don't try to access them in the ‘struct termios’ structure directly. Instead, you should use the following functions to read and store them: -- Function: speed_t cfgetospeed (const struct termios *TERMIOS-P) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the output line speed stored in the structure ‘*TERMIOS-P’. -- Function: speed_t cfgetispeed (const struct termios *TERMIOS-P) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the input line speed stored in the structure ‘*TERMIOS-P’. -- Function: int cfsetospeed (struct termios *TERMIOS-P, speed_t SPEED) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function stores SPEED in ‘*TERMIOS-P’ as the output speed. The normal return value is 0; a value of -1 indicates an error. If SPEED is not a speed, ‘cfsetospeed’ returns -1. -- Function: int cfsetispeed (struct termios *TERMIOS-P, speed_t SPEED) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function stores SPEED in ‘*TERMIOS-P’ as the input speed. The normal return value is 0; a value of -1 indicates an error. If SPEED is not a speed, ‘cfsetospeed’ returns -1. -- Function: int cfsetspeed (struct termios *TERMIOS-P, speed_t SPEED) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function stores SPEED in ‘*TERMIOS-P’ as both the input and output speeds. The normal return value is 0; a value of -1 indicates an error. If SPEED is not a speed, ‘cfsetspeed’ returns -1. This function is an extension in 4.4 BSD. -- Data Type: speed_t The ‘speed_t’ type is an unsigned integer data type used to represent line speeds. The functions ‘cfsetospeed’ and ‘cfsetispeed’ report errors only for speed values that the system simply cannot handle. If you specify a speed value that is basically acceptable, then those functions will succeed. But they do not check that a particular hardware device can actually support the specified speeds--in fact, they don't know which device you plan to set the speed for. If you use ‘tcsetattr’ to set the speed of a particular device to a value that it cannot handle, ‘tcsetattr’ returns -1. *Portability note:* In the GNU C Library, the functions above accept speeds measured in bits per second as input, and return speed values measured in bits per second. Other libraries require speeds to be indicated by special codes. For POSIX.1 portability, you must use one of the following symbols to represent the speed; their precise numeric values are system-dependent, but each name has a fixed meaning: ‘B110’ stands for 110 bps, ‘B300’ for 300 bps, and so on. There is no portable way to represent any speed but these, but these are the only speeds that typical serial lines can support. B0 B50 B75 B110 B134 B150 B200 B300 B600 B1200 B1800 B2400 B4800 B9600 B19200 B38400 B57600 B115200 B230400 B460800 BSD defines two additional speed symbols as aliases: ‘EXTA’ is an alias for ‘B19200’ and ‘EXTB’ is an alias for ‘B38400’. These aliases are obsolete.  File: libc.info, Node: Special Characters, Next: Noncanonical Input, Prev: Line Speed, Up: Terminal Modes 17.4.9 Special Characters ------------------------- In canonical input, the terminal driver recognizes a number of special characters which perform various control functions. These include the ERASE character (usually ) for editing input, and other editing characters. The INTR character (normally ‘C-c’) for sending a ‘SIGINT’ signal, and other signal-raising characters, may be available in either canonical or noncanonical input mode. All these characters are described in this section. The particular characters used are specified in the ‘c_cc’ member of the ‘struct termios’ structure. This member is an array; each element specifies the character for a particular role. Each element has a symbolic constant that stands for the index of that element--for example, ‘VINTR’ is the index of the element that specifies the INTR character, so storing ‘'='’ in ‘TERMIOS.c_cc[VINTR]’ specifies ‘=’ as the INTR character. On some systems, you can disable a particular special character function by specifying the value ‘_POSIX_VDISABLE’ for that role. This value is unequal to any possible character code. *Note Options for Files::, for more information about how to tell whether the operating system you are using supports ‘_POSIX_VDISABLE’. * Menu: * Editing Characters:: Special characters that terminate lines and delete text, and other editing functions. * Signal Characters:: Special characters that send or raise signals to or for certain classes of processes. * Start/Stop Characters:: Special characters that suspend or resume suspended output. * Other Special:: Other special characters for BSD systems: they can discard output, and print status.  File: libc.info, Node: Editing Characters, Next: Signal Characters, Up: Special Characters 17.4.9.1 Characters for Input Editing ..................................... These special characters are active only in canonical input mode. *Note Canonical or Not::. -- Macro: int VEOF This is the subscript for the EOF character in the special control character array. ‘TERMIOS.c_cc[VEOF]’ holds the character itself. The EOF character is recognized only in canonical input mode. It acts as a line terminator in the same way as a newline character, but if the EOF character is typed at the beginning of a line it causes ‘read’ to return a byte count of zero, indicating end-of-file. The EOF character itself is discarded. Usually, the EOF character is ‘C-d’. -- Macro: int VEOL This is the subscript for the EOL character in the special control character array. ‘TERMIOS.c_cc[VEOL]’ holds the character itself. The EOL character is recognized only in canonical input mode. It acts as a line terminator, just like a newline character. The EOL character is not discarded; it is read as the last character in the input line. You don't need to use the EOL character to make end a line. Just set the ICRNL flag. In fact, this is the default state of affairs. -- Macro: int VEOL2 This is the subscript for the EOL2 character in the special control character array. ‘TERMIOS.c_cc[VEOL2]’ holds the character itself. The EOL2 character works just like the EOL character (see above), but it can be a different character. Thus, you can specify two characters to terminate an input line, by setting EOL to one of them and EOL2 to the other. The EOL2 character is a BSD extension; it exists only on BSD systems and GNU/Linux and GNU/Hurd systems. -- Macro: int VERASE This is the subscript for the ERASE character in the special control character array. ‘TERMIOS.c_cc[VERASE]’ holds the character itself. The ERASE character is recognized only in canonical input mode. When the user types the erase character, the previous character typed is discarded. (If the terminal generates multibyte character sequences, this may cause more than one byte of input to be discarded.) This cannot be used to erase past the beginning of the current line of text. The ERASE character itself is discarded. Usually, the ERASE character is . -- Macro: int VWERASE This is the subscript for the WERASE character in the special control character array. ‘TERMIOS.c_cc[VWERASE]’ holds the character itself. The WERASE character is recognized only in canonical mode. It erases an entire word of prior input, and any whitespace after it; whitespace characters before the word are not erased. The definition of a "word" depends on the setting of the ‘ALTWERASE’ mode; *note Local Modes::. If the ‘ALTWERASE’ mode is not set, a word is defined as a sequence of any characters except space or tab. If the ‘ALTWERASE’ mode is set, a word is defined as a sequence of characters containing only letters, numbers, and underscores, optionally followed by one character that is not a letter, number, or underscore. The WERASE character is usually ‘C-w’. This is a BSD extension. -- Macro: int VKILL This is the subscript for the KILL character in the special control character array. ‘TERMIOS.c_cc[VKILL]’ holds the character itself. The KILL character is recognized only in canonical input mode. When the user types the kill character, the entire contents of the current line of input are discarded. The kill character itself is discarded too. The KILL character is usually ‘C-u’. -- Macro: int VREPRINT This is the subscript for the REPRINT character in the special control character array. ‘TERMIOS.c_cc[VREPRINT]’ holds the character itself. The REPRINT character is recognized only in canonical mode. It reprints the current input line. If some asynchronous output has come while you are typing, this lets you see the line you are typing clearly again. The REPRINT character is usually ‘C-r’. This is a BSD extension.  File: libc.info, Node: Signal Characters, Next: Start/Stop Characters, Prev: Editing Characters, Up: Special Characters 17.4.9.2 Characters that Cause Signals ...................................... These special characters may be active in either canonical or noncanonical input mode, but only when the ‘ISIG’ flag is set (*note Local Modes::). -- Macro: int VINTR This is the subscript for the INTR character in the special control character array. ‘TERMIOS.c_cc[VINTR]’ holds the character itself. The INTR (interrupt) character raises a ‘SIGINT’ signal for all processes in the foreground job associated with the terminal. The INTR character itself is then discarded. *Note Signal Handling::, for more information about signals. Typically, the INTR character is ‘C-c’. -- Macro: int VQUIT This is the subscript for the QUIT character in the special control character array. ‘TERMIOS.c_cc[VQUIT]’ holds the character itself. The QUIT character raises a ‘SIGQUIT’ signal for all processes in the foreground job associated with the terminal. The QUIT character itself is then discarded. *Note Signal Handling::, for more information about signals. Typically, the QUIT character is ‘C-\’. -- Macro: int VSUSP This is the subscript for the SUSP character in the special control character array. ‘TERMIOS.c_cc[VSUSP]’ holds the character itself. The SUSP (suspend) character is recognized only if the implementation supports job control (*note Job Control::). It causes a ‘SIGTSTP’ signal to be sent to all processes in the foreground job associated with the terminal. The SUSP character itself is then discarded. *Note Signal Handling::, for more information about signals. Typically, the SUSP character is ‘C-z’. Few applications disable the normal interpretation of the SUSP character. If your program does this, it should provide some other mechanism for the user to stop the job. When the user invokes this mechanism, the program should send a ‘SIGTSTP’ signal to the process group of the process, not just to the process itself. *Note Signaling Another Process::. -- Macro: int VDSUSP This is the subscript for the DSUSP character in the special control character array. ‘TERMIOS.c_cc[VDSUSP]’ holds the character itself. The DSUSP (suspend) character is recognized only if the implementation supports job control (*note Job Control::). It sends a ‘SIGTSTP’ signal, like the SUSP character, but not right away--only when the program tries to read it as input. Not all systems with job control support DSUSP; only BSD-compatible systems do (including GNU/Hurd systems). *Note Signal Handling::, for more information about signals. Typically, the DSUSP character is ‘C-y’.  File: libc.info, Node: Start/Stop Characters, Next: Other Special, Prev: Signal Characters, Up: Special Characters 17.4.9.3 Special Characters for Flow Control ............................................ These special characters may be active in either canonical or noncanonical input mode, but their use is controlled by the flags ‘IXON’ and ‘IXOFF’ (*note Input Modes::). -- Macro: int VSTART This is the subscript for the START character in the special control character array. ‘TERMIOS.c_cc[VSTART]’ holds the character itself. The START character is used to support the ‘IXON’ and ‘IXOFF’ input modes. If ‘IXON’ is set, receiving a START character resumes suspended output; the START character itself is discarded. If ‘IXANY’ is set, receiving any character at all resumes suspended output; the resuming character is not discarded unless it is the START character. If ‘IXOFF’ is set, the system may also transmit START characters to the terminal. The usual value for the START character is ‘C-q’. You may not be able to change this value--the hardware may insist on using ‘C-q’ regardless of what you specify. -- Macro: int VSTOP This is the subscript for the STOP character in the special control character array. ‘TERMIOS.c_cc[VSTOP]’ holds the character itself. The STOP character is used to support the ‘IXON’ and ‘IXOFF’ input modes. If ‘IXON’ is set, receiving a STOP character causes output to be suspended; the STOP character itself is discarded. If ‘IXOFF’ is set, the system may also transmit STOP characters to the terminal, to prevent the input queue from overflowing. The usual value for the STOP character is ‘C-s’. You may not be able to change this value--the hardware may insist on using ‘C-s’ regardless of what you specify.  File: libc.info, Node: Other Special, Prev: Start/Stop Characters, Up: Special Characters 17.4.9.4 Other Special Characters ................................. -- Macro: int VLNEXT This is the subscript for the LNEXT character in the special control character array. ‘TERMIOS.c_cc[VLNEXT]’ holds the character itself. The LNEXT character is recognized only when ‘IEXTEN’ is set, but in both canonical and noncanonical mode. It disables any special significance of the next character the user types. Even if the character would normally perform some editing function or generate a signal, it is read as a plain character. This is the analogue of the ‘C-q’ command in Emacs. "LNEXT" stands for "literal next." The LNEXT character is usually ‘C-v’. This character is available on BSD systems and GNU/Linux and GNU/Hurd systems. -- Macro: int VDISCARD This is the subscript for the DISCARD character in the special control character array. ‘TERMIOS.c_cc[VDISCARD]’ holds the character itself. The DISCARD character is recognized only when ‘IEXTEN’ is set, but in both canonical and noncanonical mode. Its effect is to toggle the discard-output flag. When this flag is set, all program output is discarded. Setting the flag also discards all output currently in the output buffer. Typing any other character resets the flag. This character is available on BSD systems and GNU/Linux and GNU/Hurd systems. -- Macro: int VSTATUS This is the subscript for the STATUS character in the special control character array. ‘TERMIOS.c_cc[VSTATUS]’ holds the character itself. The STATUS character's effect is to print out a status message about how the current process is running. The STATUS character is recognized only in canonical mode, and only if ‘NOKERNINFO’ is not set. This character is available only on BSD systems and GNU/Hurd systems.  File: libc.info, Node: Noncanonical Input, Prev: Special Characters, Up: Terminal Modes 17.4.10 Noncanonical Input -------------------------- In noncanonical input mode, the special editing characters such as ERASE and KILL are ignored. The system facilities for the user to edit input are disabled in noncanonical mode, so that all input characters (unless they are special for signal or flow-control purposes) are passed to the application program exactly as typed. It is up to the application program to give the user ways to edit the input, if appropriate. Noncanonical mode offers special parameters called MIN and TIME for controlling whether and how long to wait for input to be available. You can even use them to avoid ever waiting--to return immediately with whatever input is available, or with no input. The MIN and TIME are stored in elements of the ‘c_cc’ array, which is a member of the ‘struct termios’ structure. Each element of this array has a particular role, and each element has a symbolic constant that stands for the index of that element. ‘VMIN’ and ‘VTIME’ are the names for the indices in the array of the MIN and TIME slots. -- Macro: int VMIN This is the subscript for the MIN slot in the ‘c_cc’ array. Thus, ‘TERMIOS.c_cc[VMIN]’ is the value itself. The MIN slot is only meaningful in noncanonical input mode; it specifies the minimum number of bytes that must be available in the input queue in order for ‘read’ to return. -- Macro: int VTIME This is the subscript for the TIME slot in the ‘c_cc’ array. Thus, ‘TERMIOS.c_cc[VTIME]’ is the value itself. The TIME slot is only meaningful in noncanonical input mode; it specifies how long to wait for input before returning, in units of 0.1 seconds. The MIN and TIME values interact to determine the criterion for when ‘read’ should return; their precise meanings depend on which of them are nonzero. There are four possible cases: • Both TIME and MIN are nonzero. In this case, TIME specifies how long to wait after each input character to see if more input arrives. After the first character received, ‘read’ keeps waiting until either MIN bytes have arrived in all, or TIME elapses with no further input. ‘read’ always blocks until the first character arrives, even if TIME elapses first. ‘read’ can return more than MIN characters if more than MIN happen to be in the queue. • Both MIN and TIME are zero. In this case, ‘read’ always returns immediately with as many characters as are available in the queue, up to the number requested. If no input is immediately available, ‘read’ returns a value of zero. • MIN is zero but TIME has a nonzero value. In this case, ‘read’ waits for time TIME for input to become available; the availability of a single byte is enough to satisfy the read request and cause ‘read’ to return. When it returns, it returns as many characters as are available, up to the number requested. If no input is available before the timer expires, ‘read’ returns a value of zero. • TIME is zero but MIN has a nonzero value. In this case, ‘read’ waits until at least MIN bytes are available in the queue. At that time, ‘read’ returns as many characters as are available, up to the number requested. ‘read’ can return more than MIN characters if more than MIN happen to be in the queue. What happens if MIN is 50 and you ask to read just 10 bytes? Normally, ‘read’ waits until there are 50 bytes in the buffer (or, more generally, the wait condition described above is satisfied), and then reads 10 of them, leaving the other 40 buffered in the operating system for a subsequent call to ‘read’. *Portability note:* On some systems, the MIN and TIME slots are actually the same as the EOF and EOL slots. This causes no serious problem because the MIN and TIME slots are used only in noncanonical input and the EOF and EOL slots are used only in canonical input, but it isn't very clean. The GNU C Library allocates separate slots for these uses. -- Function: void cfmakeraw (struct termios *TERMIOS-P) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function provides an easy way to set up ‘*TERMIOS-P’ for what has traditionally been called "raw mode" in BSD. This uses noncanonical input, and turns off most processing to give an unmodified channel to the terminal. It does exactly this: TERMIOS-P->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP |INLCR|IGNCR|ICRNL|IXON); TERMIOS-P->c_oflag &= ~OPOST; TERMIOS-P->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN); TERMIOS-P->c_cflag &= ~(CSIZE|PARENB); TERMIOS-P->c_cflag |= CS8;  File: libc.info, Node: BSD Terminal Modes, Next: Line Control, Prev: Terminal Modes, Up: Low-Level Terminal Interface 17.5 BSD Terminal Modes ======================= The usual way to get and set terminal modes is with the functions described in *note Terminal Modes::. However, on some systems you can use the BSD-derived functions in this section to do some of the same things. On many systems, these functions do not exist. Even with the GNU C Library, the functions simply fail with ‘errno’ = ‘ENOSYS’ with many kernels, including Linux. The symbols used in this section are declared in ‘sgtty.h’. -- Data Type: struct sgttyb This structure is an input or output parameter list for ‘gtty’ and ‘stty’. ‘char sg_ispeed’ Line speed for input ‘char sg_ospeed’ Line speed for output ‘char sg_erase’ Erase character ‘char sg_kill’ Kill character ‘int sg_flags’ Various flags -- Function: int gtty (int FILEDES, struct sgttyb *ATTRIBUTES) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function gets the attributes of a terminal. ‘gtty’ sets *ATTRIBUTES to describe the terminal attributes of the terminal which is open with file descriptor FILEDES. -- Function: int stty (int FILEDES, const struct sgttyb *ATTRIBUTES) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function sets the attributes of a terminal. ‘stty’ sets the terminal attributes of the terminal which is open with file descriptor FILEDES to those described by *ATTRIBUTES.  File: libc.info, Node: Line Control, Next: Noncanon Example, Prev: BSD Terminal Modes, Up: Low-Level Terminal Interface 17.6 Line Control Functions =========================== These functions perform miscellaneous control actions on terminal devices. As regards terminal access, they are treated like doing output: if any of these functions is used by a background process on its controlling terminal, normally all processes in the process group are sent a ‘SIGTTOU’ signal. The exception is if the calling process itself is ignoring or blocking ‘SIGTTOU’ signals, in which case the operation is performed and no signal is sent. *Note Job Control::. -- Function: int tcsendbreak (int FILEDES, int DURATION) Preliminary: | MT-Unsafe race:tcattr(filedes)/bsd | AS-Unsafe | AC-Unsafe corrupt/bsd | *Note POSIX Safety Concepts::. This function generates a break condition by transmitting a stream of zero bits on the terminal associated with the file descriptor FILEDES. The duration of the break is controlled by the DURATION argument. If zero, the duration is between 0.25 and 0.5 seconds. The meaning of a nonzero value depends on the operating system. This function does nothing if the terminal is not an asynchronous serial data port. The return value is normally zero. In the event of an error, a value of -1 is returned. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES is not a valid file descriptor. ‘ENOTTY’ The FILEDES is not associated with a terminal device. -- Function: int tcdrain (int FILEDES) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘tcdrain’ function waits until all queued output to the terminal FILEDES has been transmitted. This function is a cancellation point in multi-threaded programs. This is a problem if the thread allocates some resources (like memory, file descriptors, semaphores or whatever) at the time ‘tcdrain’ is called. If the thread gets canceled these resources stay allocated until the program ends. To avoid this calls to ‘tcdrain’ should be protected using cancellation handlers. The return value is normally zero. In the event of an error, a value of -1 is returned. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES is not a valid file descriptor. ‘ENOTTY’ The FILEDES is not associated with a terminal device. ‘EINTR’ The operation was interrupted by delivery of a signal. *Note Interrupted Primitives::. -- Function: int tcflush (int FILEDES, int QUEUE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘tcflush’ function is used to clear the input and/or output queues associated with the terminal file FILEDES. The QUEUE argument specifies which queue(s) to clear, and can be one of the following values: ‘TCIFLUSH’ Clear any input data received, but not yet read. ‘TCOFLUSH’ Clear any output data written, but not yet transmitted. ‘TCIOFLUSH’ Clear both queued input and output. The return value is normally zero. In the event of an error, a value of -1 is returned. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES is not a valid file descriptor. ‘ENOTTY’ The FILEDES is not associated with a terminal device. ‘EINVAL’ A bad value was supplied as the QUEUE argument. It is unfortunate that this function is named ‘tcflush’, because the term "flush" is normally used for quite another operation--waiting until all output is transmitted--and using it for discarding input or output would be confusing. Unfortunately, the name ‘tcflush’ comes from POSIX and we cannot change it. -- Function: int tcflow (int FILEDES, int ACTION) Preliminary: | MT-Unsafe race:tcattr(filedes)/bsd | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. The ‘tcflow’ function is used to perform operations relating to XON/XOFF flow control on the terminal file specified by FILEDES. The ACTION argument specifies what operation to perform, and can be one of the following values: ‘TCOOFF’ Suspend transmission of output. ‘TCOON’ Restart transmission of output. ‘TCIOFF’ Transmit a STOP character. ‘TCION’ Transmit a START character. For more information about the STOP and START characters, see *note Special Characters::. The return value is normally zero. In the event of an error, a value of -1 is returned. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES is not a valid file descriptor. ‘ENOTTY’ The FILEDES is not associated with a terminal device. ‘EINVAL’ A bad value was supplied as the ACTION argument.  File: libc.info, Node: Noncanon Example, Next: getpass, Prev: Line Control, Up: Low-Level Terminal Interface 17.7 Noncanonical Mode Example ============================== Here is an example program that shows how you can set up a terminal device to read single characters in noncanonical input mode, without echo. #include #include #include #include /* Use this variable to remember original terminal attributes. */ struct termios saved_attributes; void reset_input_mode (void) { tcsetattr (STDIN_FILENO, TCSANOW, &saved_attributes); } void set_input_mode (void) { struct termios tattr; /* Make sure stdin is a terminal. */ if (!isatty (STDIN_FILENO)) { fprintf (stderr, "Not a terminal.\n"); exit (EXIT_FAILURE); } /* Save the terminal attributes so we can restore them later. */ tcgetattr (STDIN_FILENO, &saved_attributes); atexit (reset_input_mode); /* Set the funny terminal modes. */ tcgetattr (STDIN_FILENO, &tattr); tattr.c_lflag &= ~(ICANON|ECHO); /* Clear ICANON and ECHO. */ tattr.c_cc[VMIN] = 1; tattr.c_cc[VTIME] = 0; tcsetattr (STDIN_FILENO, TCSAFLUSH, &tattr); } int main (void) { char c; set_input_mode (); while (1) { read (STDIN_FILENO, &c, 1); if (c == '\004') /* ‘C-d’ */ break; else write (STDOUT_FILENO, &c, 1); } return EXIT_SUCCESS; } This program is careful to restore the original terminal modes before exiting or terminating with a signal. It uses the ‘atexit’ function (*note Cleanups on Exit::) to make sure this is done by ‘exit’. The shell is supposed to take care of resetting the terminal modes when a process is stopped or continued; see *note Job Control::. But some existing shells do not actually do this, so you may wish to establish handlers for job control signals that reset terminal modes. The above example does so.  File: libc.info, Node: getpass, Next: Pseudo-Terminals, Prev: Noncanon Example, Up: Low-Level Terminal Interface 17.8 Reading Passphrases ======================== When reading in a passphrase, it is desirable to avoid displaying it on the screen, to help keep it secret. The following function handles this in a convenient way. -- Function: char * getpass (const char *PROMPT) Preliminary: | MT-Unsafe term | AS-Unsafe heap lock corrupt | AC-Unsafe term lock corrupt | *Note POSIX Safety Concepts::. ‘getpass’ outputs PROMPT, then reads a string in from the terminal without echoing it. It tries to connect to the real terminal, ‘/dev/tty’, if possible, to encourage users not to put plaintext passphrases in files; otherwise, it uses ‘stdin’ and ‘stderr’. ‘getpass’ also disables the INTR, QUIT, and SUSP characters on the terminal using the ‘ISIG’ terminal attribute (*note Local Modes::). The terminal is flushed before and after ‘getpass’, so that characters of a mistyped passphrase are not accidentally visible. In other C libraries, ‘getpass’ may only return the first ‘PASS_MAX’ bytes of a passphrase. The GNU C Library has no limit, so ‘PASS_MAX’ is undefined. The prototype for this function is in ‘unistd.h’. ‘PASS_MAX’ would be defined in ‘limits.h’. This precise set of operations may not suit all possible situations. In this case, it is recommended that users write their own ‘getpass’ substitute. For instance, a very simple substitute is as follows: #include #include ssize_t my_getpass (char **lineptr, size_t *n, FILE *stream) { struct termios old, new; int nread; /* Turn echoing off and fail if we can't. */ if (tcgetattr (fileno (stream), &old) != 0) return -1; new = old; new.c_lflag &= ~ECHO; if (tcsetattr (fileno (stream), TCSAFLUSH, &new) != 0) return -1; /* Read the passphrase */ nread = getline (lineptr, n, stream); /* Restore terminal. */ (void) tcsetattr (fileno (stream), TCSAFLUSH, &old); return nread; } The substitute takes the same parameters as ‘getline’ (*note Line Input::); the user must print any prompt desired.  File: libc.info, Node: Pseudo-Terminals, Prev: getpass, Up: Low-Level Terminal Interface 17.9 Pseudo-Terminals ===================== A “pseudo-terminal” is a special interprocess communication channel that acts like a terminal. One end of the channel is called the “master” side or “master pseudo-terminal device”, the other side is called the “slave” side. Data written to the master side is received by the slave side as if it was the result of a user typing at an ordinary terminal, and data written to the slave side is sent to the master side as if it was written on an ordinary terminal. Pseudo terminals are the way programs like ‘xterm’ and ‘emacs’ implement their terminal emulation functionality. * Menu: * Allocation:: Allocating a pseudo terminal. * Pseudo-Terminal Pairs:: How to open both sides of a pseudo-terminal in a single operation.  File: libc.info, Node: Allocation, Next: Pseudo-Terminal Pairs, Up: Pseudo-Terminals 17.9.1 Allocating Pseudo-Terminals ---------------------------------- This subsection describes functions for allocating a pseudo-terminal, and for making this pseudo-terminal available for actual use. These functions are declared in the header file ‘stdlib.h’. -- Function: int posix_openpt (int FLAGS) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. ‘posix_openpt’ returns a new file descriptor for the next available master pseudo-terminal. In the case of an error, it returns a value of -1 instead, and sets ‘errno’ to indicate the error. *Note Opening and Closing Files:: for possible values of ‘errno’. FLAGS is a bit mask created from a bitwise OR of zero or more of the following flags: ‘O_RDWR’ Open the device for both reading and writing. It is usual to specify this flag. ‘O_NOCTTY’ Do not make the device the controlling terminal for the process. These flags are defined in ‘fcntl.h’. *Note Access Modes::. For this function to be available, ‘_XOPEN_SOURCE’ must be defined to a value greater than ‘600’. *Note Feature Test Macros::. -- Function: int getpt (void) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. ‘getpt’ is similar to ‘posix_openpt’. This function is a GNU extension and should not be used in portable programs. The ‘getpt’ function returns a new file descriptor for the next available master pseudo-terminal. The normal return value from ‘getpt’ is a non-negative integer file descriptor. In the case of an error, a value of -1 is returned instead. The following ‘errno’ conditions are defined for this function: ‘ENOENT’ There are no free master pseudo-terminals available. -- Function: int grantpt (int FILEDES) Preliminary: | MT-Safe locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘grantpt’ function changes the ownership and access permission of the slave pseudo-terminal device corresponding to the master pseudo-terminal device associated with the file descriptor FILEDES. The owner is set from the real user ID of the calling process (*note Process Persona::), and the group is set to a special group (typically “tty”) or from the real group ID of the calling process. The access permission is set such that the file is both readable and writable by the owner and only writable by the group. On some systems this function is implemented by invoking a special ‘setuid’ root program (*note How Change Persona::). As a consequence, installing a signal handler for the ‘SIGCHLD’ signal (*note Job Control Signals::) may interfere with a call to ‘grantpt’. The normal return value from ‘grantpt’ is 0; a value of -1 is returned in case of failure. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘EINVAL’ The FILEDES argument is not associated with a master pseudo-terminal device. ‘EACCES’ The slave pseudo-terminal device corresponding to the master associated with FILEDES could not be accessed. -- Function: int unlockpt (int FILEDES) Preliminary: | MT-Safe | AS-Unsafe heap/bsd | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘unlockpt’ function unlocks the slave pseudo-terminal device corresponding to the master pseudo-terminal device associated with the file descriptor FILEDES. On many systems, the slave can only be opened after unlocking, so portable applications should always call ‘unlockpt’ before trying to open the slave. The normal return value from ‘unlockpt’ is 0; a value of -1 is returned in case of failure. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘EINVAL’ The FILEDES argument is not associated with a master pseudo-terminal device. -- Function: char * ptsname (int FILEDES) Preliminary: | MT-Unsafe race:ptsname | AS-Unsafe heap/bsd | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. If the file descriptor FILEDES is associated with a master pseudo-terminal device, the ‘ptsname’ function returns a pointer to a statically-allocated, null-terminated string containing the file name of the associated slave pseudo-terminal file. This string might be overwritten by subsequent calls to ‘ptsname’. -- Function: int ptsname_r (int FILEDES, char *BUF, size_t LEN) Preliminary: | MT-Safe | AS-Unsafe heap/bsd | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘ptsname_r’ function is similar to the ‘ptsname’ function except that it places its result into the user-specified buffer starting at BUF with length LEN. This function is a GNU extension. Typical usage of these functions is illustrated by the following example: int open_pty_pair (int *amaster, int *aslave) { int master, slave; char *name; master = posix_openpt (O_RDWR | O_NOCTTY); if (master < 0) return 0; if (grantpt (master) < 0 || unlockpt (master) < 0) goto close_master; name = ptsname (master); if (name == NULL) goto close_master; slave = open (name, O_RDWR); if (slave == -1) goto close_master; *amaster = master; *aslave = slave; return 1; close_slave: close (slave); close_master: close (master); return 0; }  File: libc.info, Node: Pseudo-Terminal Pairs, Prev: Allocation, Up: Pseudo-Terminals 17.9.2 Opening a Pseudo-Terminal Pair ------------------------------------- These functions, derived from BSD, are available in the separate ‘libutil’ library, and declared in ‘pty.h’. -- Function: int openpty (int *AMASTER, int *ASLAVE, char *NAME, const struct termios *TERMP, const struct winsize *WINP) Preliminary: | MT-Safe locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function allocates and opens a pseudo-terminal pair, returning the file descriptor for the master in *AMASTER, and the file descriptor for the slave in *ASLAVE. If the argument NAME is not a null pointer, the file name of the slave pseudo-terminal device is stored in ‘*name’. If TERMP is not a null pointer, the terminal attributes of the slave are set to the ones specified in the structure that TERMP points to (*note Terminal Modes::). Likewise, if WINP is not a null pointer, the screen size of the slave is set to the values specified in the structure that WINP points to. The normal return value from ‘openpty’ is 0; a value of -1 is returned in case of failure. The following ‘errno’ conditions are defined for this function: ‘ENOENT’ There are no free pseudo-terminal pairs available. *Warning:* Using the ‘openpty’ function with NAME not set to ‘NULL’ is *very dangerous* because it provides no protection against overflowing the string NAME. You should use the ‘ttyname’ function on the file descriptor returned in *SLAVE to find out the file name of the slave pseudo-terminal device instead. -- Function: int forkpty (int *AMASTER, char *NAME, const struct termios *TERMP, const struct winsize *WINP) Preliminary: | MT-Safe locale | AS-Unsafe dlopen plugin heap lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. This function is similar to the ‘openpty’ function, but in addition, forks a new process (*note Creating a Process::) and makes the newly opened slave pseudo-terminal device the controlling terminal (*note Controlling Terminal::) for the child process. If the operation is successful, there are then both parent and child processes and both see ‘forkpty’ return, but with different values: it returns a value of 0 in the child process and returns the child's process ID in the parent process. If the allocation of a pseudo-terminal pair or the process creation failed, ‘forkpty’ returns a value of -1 in the parent process. *Warning:* The ‘forkpty’ function has the same problems with respect to the NAME argument as ‘openpty’.  File: libc.info, Node: Syslog, Next: Mathematics, Prev: Low-Level Terminal Interface, Up: Top 18 Syslog ********* This chapter describes facilities for issuing and logging messages of system administration interest. This chapter has nothing to do with programs issuing messages to their own users or keeping private logs (One would typically do that with the facilities described in *note I/O on Streams::). Most systems have a facility called "Syslog" that allows programs to submit messages of interest to system administrators and can be configured to pass these messages on in various ways, such as printing on the console, mailing to a particular person, or recording in a log file for future reference. A program uses the facilities in this chapter to submit such messages. * Menu: * Overview of Syslog:: Overview of a system's Syslog facility * Submitting Syslog Messages:: Functions to submit messages to Syslog  File: libc.info, Node: Overview of Syslog, Next: Submitting Syslog Messages, Up: Syslog 18.1 Overview of Syslog ======================= System administrators have to deal with lots of different kinds of messages from a plethora of subsystems within each system, and usually lots of systems as well. For example, an FTP server might report every connection it gets. The kernel might report hardware failures on a disk drive. A DNS server might report usage statistics at regular intervals. Some of these messages need to be brought to a system administrator's attention immediately. And it may not be just any system administrator - there may be a particular system administrator who deals with a particular kind of message. Other messages just need to be recorded for future reference if there is a problem. Still others may need to have information extracted from them by an automated process that generates monthly reports. To deal with these messages, most Unix systems have a facility called "Syslog." It is generally based on a daemon called "Syslogd" Syslogd listens for messages on a Unix domain socket named ‘/dev/log’. Based on classification information in the messages and its configuration file (usually ‘/etc/syslog.conf’), Syslogd routes them in various ways. Some of the popular routings are: • Write to the system console • Mail to a specific user • Write to a log file • Pass to another daemon • Discard Syslogd can also handle messages from other systems. It listens on the ‘syslog’ UDP port as well as the local socket for messages. Syslog can handle messages from the kernel itself. But the kernel doesn't write to ‘/dev/log’; rather, another daemon (sometimes called "Klogd") extracts messages from the kernel and passes them on to Syslog as any other process would (and it properly identifies them as messages from the kernel). Syslog can even handle messages that the kernel issued before Syslogd or Klogd was running. A Linux kernel, for example, stores startup messages in a kernel message ring and they are normally still there when Klogd later starts up. Assuming Syslogd is running by the time Klogd starts, Klogd then passes everything in the message ring to it. In order to classify messages for disposition, Syslog requires any process that submits a message to it to provide two pieces of classification information with it: facility This identifies who submitted the message. There are a small number of facilities defined. The kernel, the mail subsystem, and an FTP server are examples of recognized facilities. For the complete list, *Note syslog; vsyslog::. Keep in mind that these are essentially arbitrary classifications. "Mail subsystem" doesn't have any more meaning than the system administrator gives to it. priority This tells how important the content of the message is. Examples of defined priority values are: debug, informational, warning and critical. For the complete list, see *note syslog; vsyslog::. Except for the fact that the priorities have a defined order, the meaning of each of these priorities is entirely determined by the system administrator. A "facility/priority" is a number that indicates both the facility and the priority. *Warning:* This terminology is not universal. Some people use "level" to refer to the priority and "priority" to refer to the combination of facility and priority. A Linux kernel has a concept of a message "level," which corresponds both to a Syslog priority and to a Syslog facility/priority (It can be both because the facility code for the kernel is zero, and that makes priority and facility/priority the same value). The GNU C Library provides functions to submit messages to Syslog. They do it by writing to the ‘/dev/log’ socket. *Note Submitting Syslog Messages::. The GNU C Library functions only work to submit messages to the Syslog facility on the same system. To submit a message to the Syslog facility on another system, use the socket I/O functions to write a UDP datagram to the ‘syslog’ UDP port on that system. *Note Sockets::.  File: libc.info, Node: Submitting Syslog Messages, Prev: Overview of Syslog, Up: Syslog 18.2 Submitting Syslog Messages =============================== The GNU C Library provides functions to submit messages to the Syslog facility: * Menu: * openlog:: Open connection to Syslog * syslog; vsyslog:: Submit message to Syslog * closelog:: Close connection to Syslog * setlogmask:: Cause certain messages to be ignored * Syslog Example:: Example of all of the above These functions only work to submit messages to the Syslog facility on the same system. To submit a message to the Syslog facility on another system, use the socket I/O functions to write a UDP datagram to the ‘syslog’ UDP port on that system. *Note Sockets::.  File: libc.info, Node: openlog, Next: syslog; vsyslog, Up: Submitting Syslog Messages 18.2.1 openlog -------------- The symbols referred to in this section are declared in the file ‘syslog.h’. -- Function: void openlog (const char *IDENT, int OPTION, int FACILITY) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock fd | *Note POSIX Safety Concepts::. ‘openlog’ opens or reopens a connection to Syslog in preparation for submitting messages. IDENT is an arbitrary identification string which future ‘syslog’ invocations will prefix to each message. This is intended to identify the source of the message, and people conventionally set it to the name of the program that will submit the messages. If IDENT is NULL, or if ‘openlog’ is not called, the default identification string used in Syslog messages will be the program name, taken from argv[0]. Please note that the string pointer IDENT will be retained internally by the Syslog routines. You must not free the memory that IDENT points to. It is also dangerous to pass a reference to an automatic variable since leaving the scope would mean ending the lifetime of the variable. If you want to change the IDENT string, you must call ‘openlog’ again; overwriting the string pointed to by IDENT is not thread-safe. You can cause the Syslog routines to drop the reference to IDENT and go back to the default string (the program name taken from argv[0]), by calling ‘closelog’: *Note closelog::. In particular, if you are writing code for a shared library that might get loaded and then unloaded (e.g. a PAM module), and you use ‘openlog’, you must call ‘closelog’ before any point where your library might get unloaded, as in this example: #include void shared_library_function (void) { openlog ("mylibrary", option, priority); syslog (LOG_INFO, "shared library has been invoked"); closelog (); } Without the call to ‘closelog’, future invocations of ‘syslog’ by the program using the shared library may crash, if the library gets unloaded and the memory containing the string ‘"mylibrary"’ becomes unmapped. This is a limitation of the BSD syslog interface. ‘openlog’ may or may not open the ‘/dev/log’ socket, depending on OPTION. If it does, it tries to open it and connect it as a stream socket. If that doesn't work, it tries to open it and connect it as a datagram socket. The socket has the "Close on Exec" attribute, so the kernel will close it if the process performs an exec. You don't have to use ‘openlog’. If you call ‘syslog’ without having called ‘openlog’, ‘syslog’ just opens the connection implicitly and uses defaults for the information in IDENT and OPTIONS. OPTIONS is a bit string, with the bits as defined by the following single bit masks: ‘LOG_PERROR’ If on, ‘openlog’ sets up the connection so that any ‘syslog’ on this connection writes its message to the calling process' Standard Error stream in addition to submitting it to Syslog. If off, ‘syslog’ does not write the message to Standard Error. ‘LOG_CONS’ If on, ‘openlog’ sets up the connection so that a ‘syslog’ on this connection that fails to submit a message to Syslog writes the message instead to system console. If off, ‘syslog’ does not write to the system console (but of course Syslog may write messages it receives to the console). ‘LOG_PID’ When on, ‘openlog’ sets up the connection so that a ‘syslog’ on this connection inserts the calling process' Process ID (PID) into the message. When off, ‘openlog’ does not insert the PID. ‘LOG_NDELAY’ When on, ‘openlog’ opens and connects the ‘/dev/log’ socket. When off, a future ‘syslog’ call must open and connect the socket. *Portability note:* In early systems, the sense of this bit was exactly the opposite. ‘LOG_ODELAY’ This bit does nothing. It exists for backward compatibility. If any other bit in OPTIONS is on, the result is undefined. FACILITY is the default facility code for this connection. A ‘syslog’ on this connection that specifies default facility causes this facility to be associated with the message. See ‘syslog’ for possible values. A value of zero means the default, which is ‘LOG_USER’. If a Syslog connection is already open when you call ‘openlog’, ‘openlog’ "reopens" the connection. Reopening is like opening except that if you specify zero for the default facility code, the default facility code simply remains unchanged and if you specify LOG_NDELAY and the socket is already open and connected, ‘openlog’ just leaves it that way.  File: libc.info, Node: syslog; vsyslog, Next: closelog, Prev: openlog, Up: Submitting Syslog Messages 18.2.2 syslog, vsyslog ---------------------- The symbols referred to in this section are declared in the file ‘syslog.h’. -- Function: void syslog (int FACILITY_PRIORITY, const char *FORMAT, ...) Preliminary: | MT-Safe env locale | AS-Unsafe corrupt heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::. ‘syslog’ submits a message to the Syslog facility. It does this by writing to the Unix domain socket ‘/dev/log’. ‘syslog’ submits the message with the facility and priority indicated by FACILITY_PRIORITY. The macro ‘LOG_MAKEPRI’ generates a facility/priority from a facility and a priority, as in the following example: LOG_MAKEPRI(LOG_USER, LOG_WARNING) The possible values for the facility code are (macros): ‘LOG_USER’ A miscellaneous user process ‘LOG_MAIL’ Mail ‘LOG_DAEMON’ A miscellaneous system daemon ‘LOG_AUTH’ Security (authorization) ‘LOG_SYSLOG’ Syslog ‘LOG_LPR’ Central printer ‘LOG_NEWS’ Network news (e.g. Usenet) ‘LOG_UUCP’ UUCP ‘LOG_CRON’ Cron and At ‘LOG_AUTHPRIV’ Private security (authorization) ‘LOG_FTP’ Ftp server ‘LOG_LOCAL0’ Locally defined ‘LOG_LOCAL1’ Locally defined ‘LOG_LOCAL2’ Locally defined ‘LOG_LOCAL3’ Locally defined ‘LOG_LOCAL4’ Locally defined ‘LOG_LOCAL5’ Locally defined ‘LOG_LOCAL6’ Locally defined ‘LOG_LOCAL7’ Locally defined Results are undefined if the facility code is anything else. *NB:* ‘syslog’ recognizes one other facility code: that of the kernel. But you can't specify that facility code with these functions. If you try, it looks the same to ‘syslog’ as if you are requesting the default facility. But you wouldn't want to anyway, because any program that uses the GNU C Library is not the kernel. You can use just a priority code as FACILITY_PRIORITY. In that case, ‘syslog’ assumes the default facility established when the Syslog connection was opened. *Note Syslog Example::. The possible values for the priority code are (macros): ‘LOG_EMERG’ The message says the system is unusable. ‘LOG_ALERT’ Action on the message must be taken immediately. ‘LOG_CRIT’ The message states a critical condition. ‘LOG_ERR’ The message describes an error. ‘LOG_WARNING’ The message is a warning. ‘LOG_NOTICE’ The message describes a normal but important event. ‘LOG_INFO’ The message is purely informational. ‘LOG_DEBUG’ The message is only for debugging purposes. Results are undefined if the priority code is anything else. If the process does not presently have a Syslog connection open (i.e., it did not call ‘openlog’), ‘syslog’ implicitly opens the connection the same as ‘openlog’ would, with the following defaults for information that would otherwise be included in an ‘openlog’ call: The default identification string is the program name. The default default facility is ‘LOG_USER’. The default for all the connection options in OPTIONS is as if those bits were off. ‘syslog’ leaves the Syslog connection open. If the ‘/dev/log’ socket is not open and connected, ‘syslog’ opens and connects it, the same as ‘openlog’ with the ‘LOG_NDELAY’ option would. ‘syslog’ leaves ‘/dev/log’ open and connected unless its attempt to send the message failed, in which case ‘syslog’ closes it (with the hope that a future implicit open will restore the Syslog connection to a usable state). Example: #include syslog (LOG_MAKEPRI(LOG_LOCAL1, LOG_ERROR), "Unable to make network connection to %s. Error=%m", host); -- Function: void vsyslog (int FACILITY_PRIORITY, const char *FORMAT, va_list ARGLIST) Preliminary: | MT-Safe env locale | AS-Unsafe corrupt heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::. This is functionally identical to ‘syslog’, with the BSD style variable length argument.  File: libc.info, Node: closelog, Next: setlogmask, Prev: syslog; vsyslog, Up: Submitting Syslog Messages 18.2.3 closelog --------------- The symbols referred to in this section are declared in the file ‘syslog.h’. -- Function: void closelog (void) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock fd | *Note POSIX Safety Concepts::. ‘closelog’ closes the current Syslog connection, if there is one. This includes closing the ‘/dev/log’ socket, if it is open. ‘closelog’ also sets the identification string for Syslog messages back to the default, if ‘openlog’ was called with a non-NULL argument to IDENT. The default identification string is the program name taken from argv[0]. If you are writing shared library code that uses ‘openlog’ to generate custom syslog output, you should use ‘closelog’ to drop the GNU C Library's internal reference to the IDENT pointer when you are done. Please read the section on ‘openlog’ for more information: *Note openlog::. ‘closelog’ does not flush any buffers. You do not have to call ‘closelog’ before re-opening a Syslog connection with ‘openlog’. Syslog connections are automatically closed on exec or exit.  File: libc.info, Node: setlogmask, Next: Syslog Example, Prev: closelog, Up: Submitting Syslog Messages 18.2.4 setlogmask ----------------- The symbols referred to in this section are declared in the file ‘syslog.h’. -- Function: int setlogmask (int MASK) Preliminary: | MT-Unsafe race:LogMask | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. ‘setlogmask’ sets a mask (the "logmask") that determines which future ‘syslog’ calls shall be ignored. If a program has not called ‘setlogmask’, ‘syslog’ doesn't ignore any calls. You can use ‘setlogmask’ to specify that messages of particular priorities shall be ignored in the future. A ‘setlogmask’ call overrides any previous ‘setlogmask’ call. Note that the logmask exists entirely independently of opening and closing of Syslog connections. Setting the logmask has a similar effect to, but is not the same as, configuring Syslog. The Syslog configuration may cause Syslog to discard certain messages it receives, but the logmask causes certain messages never to get submitted to Syslog in the first place. MASK is a bit string with one bit corresponding to each of the possible message priorities. If the bit is on, ‘syslog’ handles messages of that priority normally. If it is off, ‘syslog’ discards messages of that priority. Use the message priority macros described in *note syslog; vsyslog:: and the ‘LOG_MASK’ to construct an appropriate MASK value, as in this example: LOG_MASK(LOG_EMERG) | LOG_MASK(LOG_ERROR) or ~(LOG_MASK(LOG_INFO)) There is also a ‘LOG_UPTO’ macro, which generates a mask with the bits on for a certain priority and all priorities above it: LOG_UPTO(LOG_ERROR) The unfortunate naming of the macro is due to the fact that internally, higher numbers are used for lower message priorities.  File: libc.info, Node: Syslog Example, Prev: setlogmask, Up: Submitting Syslog Messages 18.2.5 Syslog Example --------------------- Here is an example of ‘openlog’, ‘syslog’, and ‘closelog’: This example sets the logmask so that debug and informational messages get discarded without ever reaching Syslog. So the second ‘syslog’ in the example does nothing. #include setlogmask (LOG_UPTO (LOG_NOTICE)); openlog ("exampleprog", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1); syslog (LOG_NOTICE, "Program started by User %d", getuid ()); syslog (LOG_INFO, "A tree falls in a forest"); closelog ();  File: libc.info, Node: Mathematics, Next: Arithmetic, Prev: Syslog, Up: Top 19 Mathematics ************** This chapter contains information about functions for performing mathematical computations, such as trigonometric functions. Most of these functions have prototypes declared in the header file ‘math.h’. The complex-valued functions are defined in ‘complex.h’. All mathematical functions which take a floating-point argument have three variants, one each for ‘double’, ‘float’, and ‘long double’ arguments. The ‘double’ versions are mostly defined in ISO C89. The ‘float’ and ‘long double’ versions are from the numeric extensions to C included in ISO C99. Which of the three versions of a function should be used depends on the situation. For most calculations, the ‘float’ functions are the fastest. On the other hand, the ‘long double’ functions have the highest precision. ‘double’ is somewhere in between. It is usually wise to pick the narrowest type that can accommodate your data. Not all machines have a distinct ‘long double’ type; it may be the same as ‘double’. The GNU C Library also provides ‘_FloatN’ and ‘_FloatNx’ types. These types are defined in ISO/IEC TS 18661-3, which extends ISO C and defines floating-point types that are not machine-dependent. When such a type, such as ‘_Float128’, is supported by the GNU C Library, extra variants for most of the mathematical functions provided for ‘double’, ‘float’, and ‘long double’ are also provided for the supported type. Throughout this manual, the ‘_FloatN’ and ‘_FloatNx’ variants of these functions are described along with the ‘double’, ‘float’, and ‘long double’ variants and they come from ISO/IEC TS 18661-3, unless explicitly stated otherwise. Support for ‘_FloatN’ or ‘_FloatNx’ types is provided for ‘_Float32’, ‘_Float64’ and ‘_Float32x’ on all platforms. It is also provided for ‘_Float128’ and ‘_Float64x’ on powerpc64le (PowerPC 64-bits little-endian), x86_64, x86, aarch64, alpha, loongarch, mips64, riscv, s390 and sparc. * Menu: * Mathematical Constants:: Precise numeric values for often-used constants. * Trig Functions:: Sine, cosine, tangent, and friends. * Inverse Trig Functions:: Arcsine, arccosine, etc. * Exponents and Logarithms:: Also pow and sqrt. * Hyperbolic Functions:: sinh, cosh, tanh, etc. * Special Functions:: Bessel, gamma, erf. * Errors in Math Functions:: Known Maximum Errors in Math Functions. * Pseudo-Random Numbers:: Functions for generating pseudo-random numbers. * FP Function Optimizations:: Fast code or small code.