概述,源碼,
概述
對於類 Unix 系統，unistd.h 中所定義的接口通常都是大量針對系統調用的封裝（英語：wrapper functions），如 fork、pipe 以及各種 I/O 原語（read、write、close 等等）。
源碼
#ifndef _UNISTD_H#define _UNISTD_H#include <features.h>#ifdef __cplusplusextern "C" {#endif#include <_ansi.h>#include <sys/types.h>#include <sys/_types.h>#define __need_size_t#define __need_ptrdiff_t#include <stddef.h>extern char **environ;void _EXFUN(_exit, (int __status ) _ATTRIBUTE ((noreturn)));int _EXFUN(access,(const char *__path, int __amode ));unsigned _EXFUN(alarm, (unsigned __secs ));int _EXFUN(chdir, (const char *__path ));int _EXFUN(chmod, (const char *__path, mode_t __mode ));int _EXFUN(chown, (const char *__path, uid_t __owner, gid_t __group ));int _EXFUN(chroot, (const char *__path ));int _EXFUN(close, (int __fildes ));char _EXFUN(*ctermid, (char *__s ));char _EXFUN(*cuserid, (char *__s ));int _EXFUN(dup, (int __fildes ));int _EXFUN(dup2, (int __fildes, int __fildes2 ));int _EXFUN(execl, (const char *__path, const char *, ... ));int _EXFUN(execle, (const char *__path, const char *, ... ));int _EXFUN(execlp, (const char *__file, const char *, ... ));int _EXFUN(execv, (const char *__path, char * const __argv[] ));int _EXFUN(execve, (const char *__path, char * const __argv[], char * const __envp[] ));int _EXFUN(execvp, (const char *__file, char * const __argv[] ));int _EXFUN(fchdir, (int __fildes));int _EXFUN(fchmod, (int __fildes, mode_t __mode ));int _EXFUN(fchown, (int __fildes, uid_t __owner, gid_t __group ));pid_t _EXFUN(fork, (void ));long _EXFUN(fpathconf, (int __fd, int __name ));int _EXFUN(fsync, (int __fd));int _EXFUN(ftruncate, (int __fd, off_t __length));char _EXFUN(*getcwd, (char *__buf, size_t __size ));int _EXFUN(getdomainname ,(char *__name, size_t __len));gid_t _EXFUN(getegid, (void ));uid_t _EXFUN(geteuid, (void ));gid_t _EXFUN(getgid, (void ));int _EXFUN(getgroups, (int __gidsetsize, gid_t __grouplist[] ));int _EXFUN(__gethostname, (char *__name, size_t __len));char _EXFUN(*getlogin, (void ));#if defined(_POSIX_THREAD_SAFE_FUNCTIONS)int _EXFUN(getlogin_r, (char *name, size_t namesize) );#endifchar _EXFUN(*getpass, (__const char *__prompt));int _EXFUN(getpagesize, (void));pid_t _EXFUN(getpgid, (pid_t));pid_t _EXFUN(getpgrp, (void ));pid_t _EXFUN(getpid, (void ));pid_t _EXFUN(getppid, (void ));uid_t _EXFUN(getuid, (void ));char * _EXFUN(getusershell, (void));char _EXFUN(*getwd, (char *__buf ));int _EXFUN(isatty, (int __fildes ));int _EXFUN(lchown, (const char *__path, uid_t __owner, gid_t __group ));int _EXFUN(link, (const char *__path1, const char *__path2 ));int _EXFUN(nice, (int __nice_value ));off_t _EXFUN(lseek, (int __fildes, off_t __offset, int __whence ));long _EXFUN(pathconf, (const char *__path, int __name ));int _EXFUN(pause, (void ));int _EXFUN(pipe, (int __fildes[2] ));ssize_t _EXFUN(pread, (int __fd, void *__buf, size_t __nbytes, off_t __offset));ssize_t _EXFUN(pwrite, (int __fd, const void *__buf, size_t __nbytes, off_t __offset));_READ_WRITE_RETURN_TYPE _EXFUN(read, (int __fd, void *__buf, size_t __nbyte ));int _EXFUN(readlink, (const char *path, char *buf, size_t bufsiz));int _EXFUN(rmdir, (const char *__path ));void * _EXFUN(sbrk, (ptrdiff_t __incr));int _EXFUN(setegid, (gid_t __gid ));int _EXFUN(seteuid, (uid_t __uid ));int _EXFUN(setgid, (gid_t __gid ));int _EXFUN(setpgid, (pid_t __pid, pid_t __pgid ));int _EXFUN(setpgrp, (void ));pid_t _EXFUN(setsid, (void ));int _EXFUN(setuid, (uid_t __uid ));unsigned _EXFUN(sleep, (unsigned int __seconds ));void _EXFUN(swab, (const void *, void *, ssize_t));int _EXFUN(symlink, (const char *oldpath, const char *newpath));long _EXFUN(sysconf, (int __name ));pid_t _EXFUN(tcgetpgrp, (int __fildes ));int _EXFUN(tcsetpgrp, (int __fildes, pid_t __pgrp_id ));int _EXFUN(truncate, (const char *, off_t __length));char * _EXFUN(ttyname, (int __fildes ));int _EXFUN(ttyname_r, (int __fildes, char *__buf, size_t __len));int _EXFUN(unlink, (const char *__path ));int _EXFUN(usleep, (__useconds_t __useconds));int _EXFUN(vhangup, (void ));_READ_WRITE_RETURN_TYPE _EXFUN(write, (int __fd, const void *__buf, size_t __nbyte ));extern char *optarg; /** getopt(3) external variables */extern int optind, opterr, optopt;int getopt(int, char * const [], const char *);extern int optreset; /** getopt(3) external variable */#ifndef _POSIX_SOURCEpid_t _EXFUN(vfork, (void ));extern char *suboptarg; /** getsubopt(3) external variable */int getsubopt(char **, char * const *, char **);#endif /** _POSIX_SOURCE *//** Provide prototypes for most of the _<systemcall> names that areprovided in newlib for some compilers. */int _EXFUN(_close, (int __fildes ));pid_t _EXFUN(_fork, (void ));pid_t _EXFUN(_getpid, (void ));int _EXFUN(_link, (const char *__path1, const char *__path2 ));off_t _EXFUN(_lseek, (int __fildes, off_t __offset, int __whence ));_READ_WRITE_RETURN_TYPE _EXFUN(_read, (int __fd, void *__buf, size_t __nbyte ));void * _EXFUN(_sbrk, (size_t __incr));int _EXFUN(_unlink, (const char *__path ));_READ_WRITE_RETURN_TYPE _EXFUN(_write, (int __fd, const void *__buf, size_t __nbyte ));int _EXFUN(_execve, (const char *__path, char * const __argv[], char * const __envp[] ));#define F_OK 0#define R_OK 4#define W_OK 2#define X_OK 1# define SEEK_SET 0# define SEEK_CUR 1# define SEEK_END 2#include <sys/features.h>#define STDIN_FILENO 0 /** standard input file descriptor */#define STDOUT_FILENO 1 /** standard output file descriptor */#define STDERR_FILENO 2 /** standard error file descriptor */#include <bits/environments.h>#include <bits/confname.h># define MAXPATHLEN 1024#ifdef __cplusplus}#endif#endif /** _SYS_UNISTD_H *