使用stat（）函数判断文件类型

Dear 丶 2022-08-10 08:50 213阅读 0赞

一、stat()获取文件元数据

stat系统调用原型：  
\#include <sys/stat.h>

int stat(const char \*path, struct stat \*buf);  
int fstat(int fd, struct stat \*buf);  
int lstat(const char \*path, struct stat \*buf);

帮助信息可通过：man 2 stat 查看

DESCRIPTION  
These functions return information about a file. No permissions are  
required on the file itself, but — in the case of stat() and lstat() —  
execute (search) permission is required on all of the directories in  
path that [lead][] to the file.

stat() stats the file pointed to by path and fills in buf.

lstat() is identical to stat(), except that if path is a symbolic link,  
then the link itself is stat-ed, not the file that it refers to.

fstat() is identical to stat(), except that the file to be stat-ed is  
specified by the file descriptor fd.

All of these system calls return a stat structure, which contains the  
following fields:

struct stat \{  
dev\_t st\_dev; /\* ID of device containing file ：该文件所属设备的设备号，设备号包括主设备和和次设备号，dev\_t是16位整数，高8位表示主设备号，低8位表示次设备号\*/  
ino\_t st\_ino; /\* inode number \*/  
mode\_t st\_mode; /\* protection ：包含文件访问权限信息及文件类型\*/  
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)：如果该文件是特殊文件即设备文件，则表示设备号 \*/  
off\_t st\_size; /\* total size, in bytes \*/  
blksize\_t st\_blksize; /\* [block][]size for file system I/O \*/  
blkcnt\_t st\_blocks; /\* number of 512B blocks allocated ：分配的块数量\*/  
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：如修改文件的权限 \*/  
\};

文件类型有两种方式获得：

1.通过以下的一些宏进行验证：m为struct stat中得st\_mode字段

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.)

2.利用struct stat中得st\_mode字段与S\_IFMT进行与运算：mode&S\_IFMT，然后将得到的结果与下列的常量比较，相等就是

The following [flag][]s are defined for the st\_mode field:

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

文件访问权限获得：利用struct stat中得st\_mode字段与S\_IFMT进行与运算：mode&S\_IFMT，然后将得到的结果与下列的常量比较，相等就是

S\_IFMT 0170000 bit [mask][] for the file type bit fields  
  
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  
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  
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 (not in [group][])  
S\_IROTH 00004 others have read permission  
S\_IWOTH 00002 others have write permission  
S\_IXOTH 00001 others have execute permission

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