嵌入式 Linux系统编程（四）——文件属性

嵌入式 Linux系统编程（四）——文件属性

一、文件属性概述

Linux 文件的属性主要包括：文件的节点、种类、权限模式、链接数量、所归属的用户和用户组、最近访问或修改的时间等内容。文件属性示例如下：
多个文件属性查看：
ls -lih
1341714 -rw-r--r-- 1 root root 2.5K May 28 10:24 bit_marco.c
1341718 -rw-r--r-- 1 root root 2.1K May 28 09:08 bit_marco.c~
1341706 -rw-r--r-- 1 root root 2.6K May 28 08:54 bit_operaion.c
1335906 -rwxr-xr-x 1 root root 7.2K May 30 04:06 file
1341722 -rw-r--r-- 1 root root 2.7K May 30 04:06 file.c
1321584 -rw-r--r-- 1 root root 2.7K May 30 04:04 file.c~
1341708 -rwxr-xr-x 1 root root 6.4K May 28 09:08 main
1335846 -rw-r--r-- 1 root root 2.6K May 28 08:55 main.c
第一字段：inode
第二字段：文件类型和权限
第三字段：硬链接数
第四字段：所属用户
第五字段：所属用户组
第六字段：文件大小
第七字段：最后访问或修改时间
第八字段：文件名
单个文件属性详细查看：
root#stat file
File: `file'
Size: 7308 Blocks: 16 IO Block: 4096 regular file
Device: fd00h/64768d Inode: 1335906 Links: 1
Access: (0755/-rwxr-xr-x) Uid: (0/root) Gid: (0/root)
Access: 2016-05-30 04:06:10.151098056 -0400
Modify: 2016-05-30 04:06:07.227089617 -0400
Change: 2016-05-30 04:06:07.227089617 -0400

二、文件属性函数

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

int stat(const char *path, struct stat *buf);
int fstat(int fd, struct stat *buf);
int lstat(const char *path, struct stat *buf);
成功返回0，错误返回-1，并设置errno全局变量
文件属性数据结构：
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for file system I/O */
blkcnt_t st_blocks; /* number of 512B blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last status change */
};

1、stat

int stat(const char *path, struct stat *buf);
path:文件的路径，buf:指向存储文件信息的数据结构的指针

2、fstat
int fstat(int fd, struct stat *buf);
fd:文件描述符，buf:指向存储文件信息的数据结构的指针

3、lstat
int lstat(const char *path, struct stat *buf);
path:文件的路径，buf:指向存储文件信息的数据结构的指针
用于查阅链接文件的文件属性

三、文件权限信息提取

文件的文件类型和文件权限存在于文件属性数据结构中的st_mode成员。为了使用st_mode检查文件类型，POSIX标准定义了如下的宏：
S_ISREG(m) is it a regular file?
S_ISDIR(m) directory?S_ISCHR(m) character device?
S_ISBLK(m) block device?
S_ISFIFO(m) FIFO (named pipe)?
S_ISLNK(m) symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m) socket? (Not in POSIX.1-1996.)
S_IFMT 0170000 bit mask for the file type bit fields
S_IFSOCK 0140000 socket
S_IFLNK 0120000 symbolic link
S_IFREG 0100000 regular file
S_IFBLK 0060000 block device
S_IFDIR 0040000 directory
S_IFCHR 0020000 character device
S_IFIFO 0010000 FIFO
S_ISUID 0004000 set UID bit
S_ISGID 0002000 set-group-ID bit (see below)
S_ISVTX 0001000 sticky bit (see below)
S_IRWXU 00700 mask for file owner permissions//用户权限掩码
S_IRUSR 00400 owner has read permission
S_IWUSR 00200 owner has write permission
S_IXUSR 00100 owner has execute permission
S_IRWXG 00070 mask for group permissions//组权限掩码
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 mask for permissions for others //掩码
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission
文件类型的获取：
int get_stat_type(const struct stat *st, char *buf)
{
if(S_ISREG(st->st_mode))
{
sprintf(buf, "regular file");
}
if(S_ISDIR(st->st_mode))
{
sprintf(buf, "directory");
}
if(S_ISCHR(st->st_mode))
{
sprintf(buf, "charactor device");
}
if(S_ISBLK(st->st_mode))
{
sprintf(buf, "block device");
}
if(S_ISFIFO(st->st_mode))
{
sprintf(buf, "fifo file");
}
if(S_ISLNK(st->st_mode))
{
sprintf(buf, "symbloc link");
}
if(S_ISSOCK(st->st_mode))
{
sprintf(buf, "socket");
}
return 0;
}

四、程序实例

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

int print_stat(struct stat *st);

int main(int argc, char **argv)
{
if(argc < 2)
{
fprintf(stderr, "argc is less than 2\n");
fprintf(stdout, "please enter: appname filename");
return -1;
}
struct stat s;
bzero(&s, sizeof(struct stat));
stat(argv[1], &s);
print_stat(&s);
return 0;
}

int print_stat(struct stat *st)
{
if(NULL == st)
{
fprintf(stderr, "struct stat *st is NULL\n");
exit(-1);
}
printf("The device no is: %d\n", st->st_dev);
printf("The file's node number is: %d\n", st->st_ino);
printf("The file's access mode is: %d\n", st->st_mode);
printf("The file's hard link number is: %d\n", st->st_nlink);
printf("The file's user id is: %d\n", st->st_uid);
printf("The file's group id is: %d\n", st->st_gid);
printf("The file's size is: %d\n", st->st_size);
printf("The block size is: %d\n", st->st_blksize);
printf("The number of allocated blocks is: %d\n", st->st_blocks);

struct tm* pAccess_time=localtime(&(st->st_atime));
struct tm* pModify_time=localtime(&(st->st_mtime));
struct tm* pChange_time=localtime(&(st->st_ctime));
char aBuffer[64] = {0};
char mBuffer[64] = {0};
char cBuffer[64] = {0};
strftime(aBuffer, 64, "The last access time is: %Y-%m-%d %H:%M:%S \n", pAccess_time);
strftime(mBuffer, 64, "The last modify time is: %Y-%m-%d %H:%M:%S \n", pModify_time);
strftime(cBuffer, 64, "The last change time is: %Y-%m-%d %H:%M:%S \n", pChange_time);

printf(aBuffer);
printf(mBuffer);
printf(cBuffer);
return 0;
}