C语言 fstat函数

前言

一、stat系统调用

stat系统调用系列包括了fstat、stat和lstat，它们都是用来返回“相关文件状态信息”的，三者的不同之处在于设定源文件的方式不同。

二、fstat

1.功能

由文件描述符取得文件的状态。

2.相关函数

stat、lstat、chmod、chown、readlink、utime。

3.头文件

#include <sys/stat.h>
#include <unistd.h>

4.函数声明

int fstat (int filedes, struct *buf);

5.描述

fstat() 用来将参数filedes 所指向的文件状态复制到参数buf 所指向的结构中(struct stat), fstat() 与stat() 作用完全相同，不同之处在于传入的参数为已打开的文件描述符。

6.返回值

执行成功返回0，失败返回-1，错误代码保存在errno中。

7.例子

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

main()
{
   struct stat buf;
   int fd;
   fd = open ("/etc/passwd", O_RDONLY);
   fstat (fd, &buf);
   printf("/etc/passwd file size = %d\n",(int)(buf.st_size));
}

执行结果：

/etc/passwd file size = 1656

三、struct stat结构体

struct stat{
    __dev_t st_dev;		/* Device.  */
    __field64(__ino_t, __ino64_t, st_ino);  /* File serial number. */
    __mode_t st_mode;		/* File mode.  */
    __nlink_t st_nlink;		/* Link count.  */
    __uid_t st_uid;		/* User ID of the file's owner.	*/
    __gid_t st_gid;		/* Group ID of the file's group.*/
    __dev_t st_rdev;		/* Device number, if device.  */
    __dev_t __pad1;
    __field64(__off_t, __off64_t, st_size);  /* Size of file, in bytes. */
    __blksize_t st_blksize;	/* Optimal block size for I/O.  */
    int __pad2;
    __field64(__blkcnt_t, __blkcnt64_t, st_blocks);  /* 512-byte blocks */
#ifdef __USE_XOPEN2K8
    /* Nanosecond resolution timestamps are stored in a format
       equivalent to 'struct timespec'.  This is the type used
       whenever possible but the Unix namespace rules do not allow the
       identifier 'timespec' to appear in the <sys/stat.h> header.
       Therefore we have to handle the use of this header in strictly
       standard-compliant sources special.  */
    struct timespec st_atim;		/* Time of last access.  */
    struct timespec st_mtim;		/* Time of last modification.  */
    struct timespec st_ctim;		/* Time of last status change.  */
# define st_atime st_atim.tv_sec	/* Backward compatibility.  */
# define st_mtime st_mtim.tv_sec
# define st_ctime st_ctim.tv_sec
#else
    __time_t st_atime;			/* Time of last access.  */
    unsigned long int st_atimensec;	/* Nscecs of last access.  */
    __time_t st_mtime;			/* Time of last modification.  */
    unsigned long int st_mtimensec;	/* Nsecs of last modification.  */
    __time_t st_ctime;			/* Time of last status change.  */
    unsigned long int st_ctimensec;	/* Nsecs of last status change.  */
#endif
    int __glibc_reserved[2];
};