malloced 2d array passed to qsort

I have the following code to add directory contents to a malloc'ed array of pointers to arrays.

However, after passing the 2d array to qsort, qsort returns nothing in the array.

array here = (null)

If i take the qsort out, the print_dir() prints the array nicely.

Am i missing something?

Code:

	
	int  n = 100;
	char **names_array;

	names_array = malloc(num_of_files * sizeof(char *));
	if(names_array == NULL)
	{
		fprintf(stderr, "out of memory\n");
	}
	for(i = 0; i < nrows; i++)
	{
		names_array[i] = malloc(n * sizeof(char));
		if(names_array[i] == NULL)
		{
			fprintf(stderr, "out of memory\n");
		}
	}


	if ( (dirp = opendir(current_dir)) != NULL )
	{
		i = 0;
	  	while ( (direntp = readdir( dirp )) != NULL )
		{
			names_array[i][n-1] = '\0';

		    strcpy(names_array[i], direntp->d_name);
		
			printf("array here = %s\n", names_array[i]);

			i++;
	     }
			
	     qsort(names_array,num_of_files ,1024, qsort_contents);
		 printf("array here = %s\n", names_array[0]);
		 print_dir(names_array, num_of_files, 1, flags);

	}

> qsort(names_array,num_of_files ,1024, qsort_contents);
1. You didn't post your compare function. Getting compare functions right can be a tricky problem

2. You specified the wrong number of elements - it should be the 'i' variable which you counted with.
Ditto for when you print them out - only print what's valid.

3. You specified the wrong size for each element of the array - where did 1024 come from???

Try for example

Code:

qsort(names_array, i, sizeof names_array[0], qsort_contents );

Code:

names_array[i][n-1] = '\0';

The above line is unnecessary -- strcpy() will null-terminate the string. And if you use strdup() instead of strcpy() it not necessary to allocate the memory ahead of time, so you can delete the previous loop that calls malloc() entirely. strdup() will allocate the required amount of space, copy the string into that memory, and return the pointer.

cheers Ancient Dragon nice tip.

Originally Posted by Salem

> qsort(names_array,num_of_files ,1024, qsort_contents);
1. You didn't post your compare function. Getting compare functions right can be a tricky problem

2. You specified the wrong number of elements - it should be the 'i' variable which you counted with.
Ditto for when you print them out - only print what's valid.

3. You specified the wrong size for each element of the array - where did 1024 come from???

Try for example

Code:

qsort(names_array, i, sizeof names_array[0], qsort_contents );

PHP Code:

int qsort_contents(const void* name1, const void* name2)
{
  /* check the first file names first characted so we know if we need 
     to skip this characted when comparing the strings*/

 
  int i = 0;

  /* if the first names 1st char is not a letter */
    if (( ( (char *)name1)[0] < 'A') || ( ((char *)name1)[0] > 'z' ) )
    {
      /* if the second names 1st char is also not a letter */
        if (( ( (char *)name2)[0] < 'A') || ( ((char *)name2)[0] > 'z' ) )
      {
        return strcmp( &((char *)name1)[1], &((char *)name2)[1]);
      }
    /* if just the first names 1st char is not a letter*/
    else
      {
        
        return strcmp( &((char *)name1)[1], ((char *)name2));
      }
    }
    /* if the second names 1st char is not a letter */
  else if (( ( (char *)name2)[0] < 'A') || ( ((char *)name2)[0] > 'z' ) )
    {
      return strcmp(((char *)name1), &((char *)name2)[1]);
    }

    return strcmp( (char*)name1, (char *)name2);

} 


I changed the call to qsort, however its not returned the contents in sorted order.

Here

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* we get here, the equivalent of char** */
/* since qsort effectively calls  cmp(&a[x],&a[y]) */
int cmp ( const void *a, const void *b ) {
  const char *const *pa = a;
  const char *const *pb = b;
  return strcmp ( *pa, *pb );
}

void show ( char *arr[], int n ) {
  int i;
  for ( i = 0 ; i < n ; i++ ) {
    printf( "%s\n", arr[i] );
  }
  printf( "--\n\n" );
}

int main ( ) {
  char *test[] = {
    "this", "is", "an", "example"
  };
  show ( test, 4 );
  qsort ( test, 4, sizeof test[0], cmp );
  show ( test, 4 );
  return 0;
}

And please use code tags, not php tags in future.

> strdup() will allocate the required amount of space, copy the string into that memory, and return the pointer.
strdup() is not a standard function.

Code:

int cmp ( const void *a, const void *b ) {
  return strcmp ( (const char*)a, (const char*)b);
}

The compare function only needs to be like this.

Originally Posted by Salem

Here

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* we get here, the equivalent of char** */
/* since qsort effectively calls  cmp(&a[x],&a[y]) */
int cmp ( const void *a, const void *b ) {
  const char *const *pa = a;
  const char *const *pb = b;
  return strcmp ( *pa, *pb );
}

void show ( char *arr[], int n ) {
  int i;
  for ( i = 0 ; i < n ; i++ ) {
    printf( "%s\n", arr[i] );
  }
  printf( "--\n\n" );
}

int main ( ) {
  char *test[] = {
    "this", "is", "an", "example"
  };
  show ( test, 4 );
  qsort ( test, 4, sizeof test[0], cmp );
  show ( test, 4 );
  return 0;
}

And please use code tags, not php tags in future.

> strdup() will allocate the required amount of space, copy the string into that memory, and return the pointer.
strdup() is not a standard function.

Thanks salem very helpful of you

> The compare function only needs to be like this.
Look again - I put your code into my program, and ....

nothing happened - I guess my pointers are already in order.