qsort - C stdlib.h

Type

function

From


<cstdlib>
<stdlib.h>

Description

Sort elements of array using quick sort algorithm

Prototype

void qsort (void* base,
            size_t num,
            size_t size,
            int (*compare)(const void*,const void*));

Parameters

Parameter	Description
base	Pointer to the array to be sorted.
num	Number of elements in the array.
size	Size in bytes of each element in the array.
compare	Pointer to a function that compares two elements.

compare function has the following prototype.

int compare (const void* p1, const void* p2);

The above function should return the following value:

return value	meaning
<0	p1 goes before p2
0	p1 is equivalent to p2
>0	p1 goes after p2

A general compare function may look like:

int compareMyType (const void * a, const void * b)
{
  if ( *(MyType*)a <  *(MyType*)b ) return -1;
  if ( *(MyType*)a == *(MyType*)b ) return 0;
  if ( *(MyType*)a >  *(MyType*)b ) return 1;
}

Return Value

none

Demo Code


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

int values[] = { 4, 1, 10, 9, 2, 25, -1, -2, -10 };

int compare (const void * a, const void * b)
{
  return ( *(int*)a - *(int*)b );
}

int main ()/*from   w ww . j  av a2  s.c om*/
{
  int n;

  qsort (values, 6, sizeof(int), compare);

  for (n=0; n<6; n++)
     printf ("%d ",values[n]);
  return 0;
}