Question

Well, I´m doing and ls program in C and I have a problem. I have to show the file permissions with this format:

drwxr-xr-x

But I get the permissions as a int because this return me this value as a int:

lstat(file->d_name, &info);
printf("%d \n", info.st_mode);

This shows for exemple: $ 33188

How can I convert the int permissions to drwxr-xr-x?

Thanks very much.

Regards.

Answer 1

The mode of a file is a bitset of permissions and file type field. These flags are defined in man stat.h.

You can extract the information from the mode like this:

switch(mode & S_IFMT) {
  case S_IFDIR:
    mode_text[0] = 'd';
    break;
  /* add other possibilities here */
  default:
    mode_text[0] = '-';
}
mode_text[1]= (mode & S_IRUSR) ? 'r' : '-';
mode_text[2]= (mode & S_IWUSR) ? 'w' : '-';
/* the third one is special; can indicates setuid as well */
mode_text[3]= (mode & S_IXUSR) ? (mode & S_ISUID) ? 's' : 'x' : '-';

etc. for group, others.