#include <unistd.h> exist in Linux, functions that contain system services

#include <unistd.h>

Linux Standard library # include <unistd.h> with Windows # include <windows.h> (C language Development)

#include <unistd.h>

Symbolic constants

is the POSIX standard-defined UNIX class system that defines symbolic constants for the header files that contain many of the UNIX system services ' function prototypes, such as the Read function, the Write function, and the Getpid function
Unistd.h is similar to the windows.h! in Windows in Unix #ifdef WIN32 #include <windows.h> #else #include <unistd.h> #endif

Unistd.h contains constants and functions:

ssize_t      Read (int, void *, size_t); int           unlink (const char *); ssize_t      write (int, const void *, size_t); int          usleep (useconds_t); unsigned     Sleep (unsigned);

int Access(const char *, int); unsigned alarm(unsigned); int chdir(const char *); int chown(const char *, uid_t, gid_t); int close(int); size_t confstr(int, char *, size_t); void _exit(int); pid_t fork(void);

NULL//NULL pointer seek_cur//Set file offset to current plus offset. Seek_end//Set file offset to EOF plus offset. Seek_set//SET file offset to offset.

About Windows.h: http://baike.baidu.com/view/1586331.htm