Use St_mode to determine file types in Linux

 use St_mode to determine file types in Linux2012-12-11 12:41 14214 People read Comments (4) favorite reports Classification:Linux (8)C + + (+)

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

In Linux, you can use the stat () function to get the state of a file [CPP]View PlainCopy

1. #include <sys/stat.h>
2. #include <unistd.h>
4. int stat (const char *file_name, struct stat *buf);

This function performs a successful return of 0, and the failure returns-1. The obtained file status is stored in the struct stat structure that the BUF pointer points to, and the struct stat is defined as follows: [CPP]View PlainCopy

2. struct STAT
4. {
6. dev_t St_dev; /* ID of device containing file-id*/of the devices on which the file resides
8. ino_t St_ino; / * Inode number-inode Node number * /
10. mode_t St_mode; /* File type and access permissions */
12. nlink_t St_nlink; / * Number of hard links-how many connections to this file are linked to (rigid connection) */
14. uid_t St_uid; / * User ID of Owner-user id*/
16. gid_t St_gid; / * Group ID of Owner-group id*/
18. dev_t St_rdev; / * Device ID (if special file)-unit number, for device file * /
20. off_t st_size; /* Total size, in bytes-File size, Bytes */
22. blksize_t st_blksize; /* BlockSize for filesystem I/O-the size of the system block */
24. blkcnt_t st_blocks; /* Number of blocks allocated-file occupies */
26. time_t st_atime; /* Time of last access-recent access times */
28. time_t st_mtime; /* Time of last modification-most recent modified */
30. time_t st_ctime; /* Time of last status change-*/
32. };

Where st_mode this variable is used to determine the file type.

St_mode is a feature bit to represent a file type, the feature bit is defined as follows:

[CPP]View PlainCopy

2. S_ifmt 0170000 file Type bit mask
4. S_ifsock 0140000 Socket
6. S_iflnk 0120000 Symbolic Link (symbolic link)
8. S_ifreg 1,000,001-like file
10. S_IFBLK 0060000 block Unit (block device)
12. S_ifdir 0040000 Catalogue
14. S_IFCHR 0020000 character unit (character device)
16. S_ififo 0010000 FIFO
18. S_isuid 0004000 file (set User-id on execution) bit
20. S_isgid 0002000 file (set Group-id on execution) bit
22. Sticky bits of s_isvtx 0001000 file
24. S_irwxu 00700 file Owner's matte value (that is, ownership limit)
26. S_irusr 00400 file owner with readable permissions
28. S_iwusr 00200 file owner with writable permission
30. S_ixusr 00100 file owner with executable permissions
32. S_IRWXG 00070 User Group mask value (i.e., ownership limit value)
34. S_IRGRP 00040 user groups with readable permissions
36. S_IWGRP 00020 user groups with writable permissions
38. S_IXGRP 00010 user groups with executable permissions
40. S_irwxo 00007 Mask value for other users (i.e., ownership limit)
42. S_iroth 00004 Other users have read access
44. S_iwoth 00002 Other users have writable permissions
46. S_ixoth 00001 other users with executable permissions
48. From the Linux C function Library Reference manual

When judging the file type, use the St_mode value of the file to compare with the value given above. Like what:

[CPP]View PlainCopy

2. #include <sys/stat.h>
4. #include <unistd.h>
6. #include <stdio.h>
10. int main ()
12. {
14. int ABC;
16. struct stat buf;
18. Stat ("/Home", &BUF);
20. ABC = buf.st_mode & S_ifdir; //with the corresponding sign phase and
22. if (abc = = S_IFDIR) //result vs. flag bit
24. printf ("It ' s a directory.\n");
26. return 0;
28. }

Operation Result:

It ' s a directory.

There is a simple way to do this, and the file type defines the macro definitions that check these types in POSIX:

[CPP]View PlainCopy

1. S_islingk (St_mode) to determine if a bit symbolic link
2. S_isreg (St_mode) is a generic file
3. S_isdir (St_mode) is a directory
4. S_ISCHR (St_mode) is a bit character device file
5. S_ISBLK (s3e) whether FIFO
6. S_issock (St_mode) is the socket

It can be judged based on the return value of these functions, and if so, 1 is returned. (I tried it, as if it were) from: http://blog.csdn.net/simmerlee/article/details/8281399

Use St_mode to determine file types in Linux