Thread: malloced 2d array passed to qsort

> 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.

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.