如何在C/C++中以编程方式读取linux文件权限

Question

如何以编程方式读取linux文件权限,而不是使用"ls"然后解析结果.

Answer 1

该stat(2)系统调用返回一个struct stat包含st_mode成员.这是ls -l显示的模式位.

在我的系统上,该man 2 stat页面显示:

   The following flags are defined for the st_mode field:

   S_IFMT     0170000   bitmask for the file type bitfields
   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
   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

Answer 2

这是C中的一个函数,它以字符串格式"rwxr-r--"返回文件权限

char* permissions(char *file){
    struct stat st;
    char *modeval = malloc(sizeof(char) * 9 + 1);
    if(stat(file, &st) == 0){
        mode_t perm = st.st_mode;
        modeval[0] = (perm & S_IRUSR) ? 'r' : '-';
        modeval[1] = (perm & S_IWUSR) ? 'w' : '-';
        modeval[2] = (perm & S_IXUSR) ? 'x' : '-';
        modeval[3] = (perm & S_IRGRP) ? 'r' : '-';
        modeval[4] = (perm & S_IWGRP) ? 'w' : '-';
        modeval[5] = (perm & S_IXGRP) ? 'x' : '-';
        modeval[6] = (perm & S_IROTH) ? 'r' : '-';
        modeval[7] = (perm & S_IWOTH) ? 'w' : '-';
        modeval[8] = (perm & S_IXOTH) ? 'x' : '-';
        modeval[9] = '\0';
        return modeval;     
    }
    else{
        return strerror(errno);
    }   
}