4.2 stat函数-读取文件属性

stat函数用于获取文件的属性信息（例如文件类型、访问权限和访问时间等）。函数原型如下：

#include <sys/stat.h>
int stat(const char *restrict pathname, struct stat *restrict buf);

返回值：成功返回0，出错返回-1。

参数：

1、pathname 文件路径

2、buf存储struct stat结构信息的缓冲区。

其中struct stat结构定义在文件<sys/stat.h>中。实际定义在<bits/stat.h>中，因为<sys/stat.h>包含了<bits/stat.h>

头文件中对struct stat结构的定义很复杂，但实际我们比较关心其中一些常用数据成员：st_mode（文件权限方面的属性）、st_uid（文件用户ID）、st_gid（文件组ID）、st_atime（数据的最后访问时间）、st_mtime（数据的最后修改时间）、st_ctime（i节点最后更改时间）、st_blksize（文件的块大小）、st_blocks（文件包含的块数）和st_size（文件大小字节数）

简化后的struct stat结构是这样：

struct stat
  {
    __dev_t st_dev;			/* Device.  */
    unsigned short int __pad1;
    __ino_t __st_ino;			/* 32bit 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.  */
    unsigned short int __pad2;
    __off_t st_size;			/* Size of file, in bytes.  */
    __blksize_t st_blksize;		/* Optimal block size for I/O.  */
    __blkcnt_t st_blocks;		/* Number 512-byte blocks allocated. */
    __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.  */
  };

<bits/stat.h>对struct stat结构的定义原文如下：

struct stat
  {
    __dev_t st_dev;			/* Device.  */
    unsigned short int __pad1;
#ifndef __USE_FILE_OFFSET64
    __ino_t st_ino;			/* File serial number.	*/
#else
    __ino_t __st_ino;			/* 32bit file serial number.	*/
#endif
    __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.  */
    unsigned short int __pad2;
#ifndef __USE_FILE_OFFSET64
    __off_t st_size;			/* Size of file, in bytes.  */
#else
    __off64_t st_size;			/* Size of file, in bytes.  */
#endif
    __blksize_t st_blksize;		/* Optimal block size for I/O.  */

#ifndef __USE_FILE_OFFSET64
    __blkcnt_t st_blocks;		/* Number 512-byte blocks allocated. */
#else
    __blkcnt64_t st_blocks;		/* Number 512-byte blocks allocated. */
#endif
#if defined __USE_MISC || defined __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
#ifndef __USE_FILE_OFFSET64
    unsigned long int __unused4;
    unsigned long int __unused5;
#else
    __ino64_t st_ino;			/* File serial number.	*/
#endif
  };

#ifdef __USE_LARGEFILE64
struct stat64
  {
    __dev_t st_dev;			/* Device.  */
    unsigned int __pad1;

    __ino_t __st_ino;			/* 32bit 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.  */
    unsigned int __pad2;
    __off64_t st_size;			/* Size of file, in bytes.  */
    __blksize_t st_blksize;		/* Optimal block size for I/O.  */

    __blkcnt64_t st_blocks;		/* Number 512-byte blocks allocated. */
# if defined __USE_MISC || defined __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.  */
# 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
    __ino64_t st_ino;			/* File serial number.		*/
  };
#endif

实例 x.4.2.1.c

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

int main(void)
{
    char            pathname[] = "/tmp/myfile";  /*文件路径*/
    struct stat     buf;                         /*属性信息*/

    if (stat(pathname, &buf) == -1) {            /*调用stat将文件属性信息放入buf*/
        printf("stat error for %s\n",pathname);
        exit(1);
    } else {
        printf("stat OK for %s\n",pathname);
        exit(0);
    }
    exit(0);
}

编译与执行：

[root@localhost unixc]# echo 'This is my tempfile!' > /tmp/myfile
[root@localhost unixc]# cat /tmp/myfile
This is my tempfile!
[root@localhost unixc]# cc x.4.2.1.c
[root@localhost unixc]# ./a.out
stat OK for /tmp/myfile
[root@localhost unixc]#