6.19.27 qsort Function

Sort an array of objects.

Include

<stdlib.h>

Prototype

void qsort(void * base, size_t nmemb, size_t size, int (* compar)(const void *, const void *));

Argument

base

the array to sort

nmemb

the number of objects in the array

size

the size of each object being sorted

compar

the comparison function to be used

Remarks

The qsort function orders the elements in the base array so that they are in an ascending order, as specified by the function pointed to by compar. The comparison function should take two arguments, and should return an integer value less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

Example

See the notes at the beginning of this chapter or section for information on using printf() or scanf() (and other functions reading and writing the stdin or stdout streams) in the example code.

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

int cmp (int *num1, int *num2)
{
  if (*num1 < *num2)
    return -1;
  if (*num1 > *num2)
    return 1;
  return 0;
}

int main (void)
{
  int array[] = {12, 92, 0, -1, 6, -24, 101};
  size_t arraylen = sizeof(array) / sizeof(int);

  qsort (array, arraylen, sizeof(int), (int (*)(const void *, const void *)) cmp);
  printf("Array elements:\n");
  for (int i=0; i != arraylen; i++) {
    printf("%d%s", array[i], i==arraylen-1 ? "\n" : " ");
  }
}

Example Output

Array elements:
-24 -1 0 6 12 92 101