printing directories code on UNIX makes error

Question

I've been studying UNIX and there's a example code on the book,

but this code seems not working. When I compile the code, returns segmentation error.

#include<dirent.h>
#include<stdlib.h>
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>

int my_double_ls(const char *name)
{
   struct dirent *d;
   DIR *dp;

   if ((dp=opendir(name)) == NULL)
    return (-1);

   while (d=readdir(dp)) {
    if (d->d_ino != 0)
        printf("%s\n", d->d_name);
   }

   rewinddir(dp);

  while (d = readdir(dp)) {
    if (d->d_ino != 0)
        printf("%s\n", d->d_name);
  }

  closedir(dp);
  return(0);
}

int main(int argc, char **argv){

  my_double_ls(argv[1]);

  return(0);
}

Answer 1

You probably invoked the program without command line arguments:

Try this:

...
int main(int argc, char **argv){
  if (argc < 2)
  {
     printf("You need to specify the directory.\n");
     exit(1);
  }

  my_double_ls(argv[1]);
  return 0;
}

The my_double_ls function looks more or less correct to me.