問題
途中使用的命令是cl.exe，在執行命令的時候找不到對應的unistd.h文件。
unistd.h是Unix系統的文件，因此，十有八九，使用的是Windows系統。下面的代碼可以修復，但是如果修復了unistd.h，很大概率你還會有更多個*.h文件找不到。勸退。
解決
找到這個編譯器所在的文件夾的include文件夾，並且unistd.h文件復制進去即可。可以新建一個文本文件，把名字和后綴名改為unistd.h。
#ifndef _UNISTD_H
#define _UNISTD_H 1
/* This is intended as a drop-in replacement for unistd.h on Windows.
* Please add functionality as neeeded.
* https://stackoverflow.com/a/826027/1202830
*/
#include <stdlib.h>
#include <io.h>
#include <getopt.h> /* getopt at: https://gist.github.com/ashelly/7776712 */
#include <process.h> /* for getpid() and the exec..() family */
#include <direct.h> /* for _getcwd() and _chdir() */
#define srandom srand
#define random rand
/* Values for the second argument to access.
These may be OR'd together. */
#define R_OK 4 /* Test for read permission. */
#define W_OK 2 /* Test for write permission. */
//#define X_OK 1 /* execute permission - unsupported in windows*/
#define F_OK 0 /* Test for existence. */
#define access _access
#define dup2 _dup2
#define execve _execve
#define ftruncate _chsize
#define unlink _unlink
#define fileno _fileno
#define getcwd _getcwd
#define chdir _chdir
#define isatty _isatty
#define lseek _lseek
/* read, write, and close are NOT being #defined here, because while there are file handle specific versions for Windows, they probably don't work for sockets. You need to look at your app and consider whether to call e.g. closesocket(). */
#ifdef _WIN64
#define ssize_t __int64
#else
#define ssize_t long
#endif
#define STDIN_FILENO 0
#define STDOUT_FILENO 1
#define STDERR_FILENO 2
/* should be in some equivalent to <sys/types.h> */
typedef __int8 int8_t;
typedef __int16 int16_t;
typedef __int32 int32_t;
typedef __int64 int64_t;
typedef unsigned __int8 uint8_t;
typedef unsigned __int16 uint16_t;
typedef unsigned __int32 uint32_t;
typedef unsigned __int64 uint64_t;
#endif /* unistd.h */
Windows的通病
這樣是不可行的，在許多情況下。原因是這個頭文件是unix, standard的縮寫，只有unix系統（Linux, Mac OS）才有。因此我們需要找到對應的Windows標准庫，就是 io.h，把包含是unistd.h的地方，都替換成io.h即可。