那位牛人解释下宏S_ISDIR()的定义呢?

Com_Net

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sunlan

判断一个路径是否是目录。

1. 
   
2. The following symbolic names for the values of type mode_t shall also be defined.
   
3. 
   
4. File type:
   
5. 
   
6. S_IFMT
   
7. Type of file.
   
8. S_IFBLK
   
9. Block special.
   
10. S_IFCHR
    
11. Character special.
    
12. S_IFIFO
    
13. FIFO special.
    
14. S_IFREG
    
15. Regular.
    
16. S_IFDIR
    
17. Directory.
    
18. S_IFLNK
    
19. Symbolic link.
    
20. S_IFSOCK
    
21. Socket.  
    
22. File mode bits:
    
23. 
    
24. S_IRWXU
    
25. Read, write, execute/search by owner.
    
26. S_IRUSR
    
27. Read permission, owner.
    
28. S_IWUSR
    
29. Write permission, owner.
    
30. S_IXUSR
    
31. Execute/search permission, owner.
    
32. S_IRWXG
    
33. Read, write, execute/search by group.
    
34. S_IRGRP
    
35. Read permission, group.
    
36. S_IWGRP
    
37. Write permission, group.
    
38. S_IXGRP
    
39. Execute/search permission, group.
    
40. S_IRWXO
    
41. Read, write, execute/search by others.
    
42. S_IROTH
    
43. Read permission, others.
    
44. S_IWOTH
    
45. Write permission, others.
    
46. S_IXOTH
    
47. Execute/search permission, others.
    
48. S_ISUID
    
49. Set-user-ID on execution.
    
50. S_ISGID
    
51. Set-group-ID on execution.
    
52. S_ISVTX
    
53. [XSI]  On directories, restricted deletion flag.  
    
54. The bits defined by S_IRUSR, S_IWUSR, S_IXUSR, S_IRGRP, S_IWGRP, S_IXGRP, S_IROTH, S_IWOTH, S_IXOTH, S_ISUID, S_ISGID, [XSI]   and S_ISVTX   shall be unique.
    
55. 
    
56. S_IRWXU is the bitwise-inclusive OR of S_IRUSR, S_IWUSR, and S_IXUSR.
    
57. 
    
58. S_IRWXG is the bitwise-inclusive OR of S_IRGRP, S_IWGRP, and S_IXGRP.
    
59. 
    
60. S_IRWXO is the bitwise-inclusive OR of S_IROTH, S_IWOTH, and S_IXOTH.
    
61. 
    
62. Implementations may OR other implementation-defined bits into S_IRWXU, S_IRWXG, and S_IRWXO, but they shall not overlap any of the other bits defined in this volume of IEEE Std 1003.1-2001. The file permission bits are defined to be those corresponding to the bitwise-inclusive OR of S_IRWXU, S_IRWXG, and S_IRWXO.
    
63. 
    
64. The following macros shall be provided to test whether a file is of the specified type. The value m supplied to the macros is the value of st_mode from a stat structure. The macro shall evaluate to a non-zero value if the test is true; 0 if the test is false.
    
65. 
    
66. S_ISBLK(m)
    
67. Test for a block special file.
    
68. S_ISCHR(m)
    
69. Test for a character special file.
    
70. S_ISDIR(m)
    
71. Test for a directory.
    
72. S_ISFIFO(m)
    
73. Test for a pipe or FIFO special file.
    
74. S_ISREG(m)
    
75. Test for a regular file.
    
76. S_ISLNK(m)
    
77. Test for a symbolic link.
    
78. S_ISSOCK(m)
    
79. Test for a socket.
    

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但是这些宏不一定被所有的系统支持。例如sco openserver就不支持S_ISSOCK(m)

Com_Net

为什么是判断啊?

#  defing  S_ISDIR(MODE)    宏是一个参数啊?

sunlan

原帖由 "Com_Net" 发表：
为什么是判断啊?

#  defing  S_ISDIR(MODE)    宏是一个参数啊?

man stat
查看<sys/stat.h>;

zalem

好像是像下面这样定义的，APUE里面说过

#define S_ISDIR(x)  (((x)&STAT_MASK)==STAT_DIR_FLAG)

Com_Net

楼上:
       可否解释下这个宏啊?

zalem

如果       x ->;           001101010101
STAT_MASK ->;        001000001010
STAT_DIR_FLAG->;  001000000000

那么就返回true阿，估计是这么回事

Com_Net

谢过楼上各位!

zalem

比如说x是16位，上8位管文件类型，下8位管access权限。
然后有两个mask 一个类型mask是0xff00,另一个权限mask是0x00ff
然后dir_flag 为 0x0100,
      reg_flag为 0x0200,。。。相互不同
     rd_flag     0x0001
     wr_flag     0x0002 。。。也都不同。
这样用不通的mask就同时可以看是什么类型又可以看是什么权限阿

Com_Net

楼上:
      不大明白,可否详细些啊?