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

#include

#include

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

#include

#include

#include

#include

#include

#include

int print_stat(struct stat *st);

int main(int argc, char **argv)

{

if(argc

{

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;

}