C语言 fstat函数

系列文章目录

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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 
#include 

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 
#include 
#include 
#include 
#include 

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  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];
};