stat() doesn't work on parent directory

Question

I'm trying to code the ls command in C, but stat() refuse to open any other directory.

 ~/Desktop/ls$ cat bug.c 
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <stdlib.h>
#include <stdio.h>
#include <pwd.h>
#include <grp.h>
#include <time.h>
#include <unistd.h>

int     main(int ac, char **av)
{
  DIR       *d;
  struct dirent *dir;
  struct stat   file;

  d = opendir(av[1]);
  if (d)
    {
      while ((dir = readdir(d)) != NULL)
        {
          printf("%s ->", dir->d_name);
          if (lstat(dir->d_name, &file) < 0)
          printf(" can't read file %s!", dir->d_name);
          printf("\n");
        }
    }
  closedir(d);
  return (0);
}

When running ./a.out . or any subfolder, it works correctly. But if I write ./a.out .. , it fails to open files...

~/Desktop/ls$ ./a.out ..
.. ->
fkdkfdjkfdkfjdfkdfjkdfjkdjkfdkjf -> can't read file fkdkfdjkfdkfjdfkdfjkdfjkdjkfdkjf!
ss -> can't read file ss!
ls -> can't read file ls!
. ->
tg -> can't read file tg!

./a.out /home/login/Desktop doesn't work either, but ./a.out /home/login/Desktop/ls/ display correctly the content of the current folder.

It looks like a.out can't open parents dir, but ls -l gives :

-rwxrwxr-x 1 hellomynameis hellomynameis 13360 nov.  25 09:56 a.out

Am I doing it the wrong way ?

Thanks !

Answer 1

Your lstat call is wrong. When you get a name from the opened directory, it is a relative name, so you need to convert it to a correct path to let lstat locate the file:

char path[...];
sprintf(path,"%s/%s",av[1],dir->d_name);
lstat(path,...);

Answer 2

The program a.out may has not permission to read all the files in that folder. Try to run a.out with root permission.

And, if you want to check the error, please print the errno to get the detail of error when the lstat function does not execute success.