/*
    In this example we demonstrate how to use a function pointer as a parameter
    to a function. We use the library function qsort.
    Note: The function pointer argument is a pointer to a user-supplied function
    that compares two elements and returns a value specifying their relationship.
*/

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

/*
User-suplied function.
The user-suplied function must return an integer value that is
    <0 if first element is less than second element
    =0 if the two elements are equivalent
    >0 if first element is greater than second element
*/
int sort_function( const void *a, const void *b)
{
    return *(int *)(a)-*(int *)(b);
}

int int_list[5] = { 1, 5, 4, 2, 3 };

void main(void)
{
    int x;

/*
    Print numbers before sorting
*/
    printf("Before sorting ...\n");
    for (x = 0; x < 5; x++)
        printf("%d\n", int_list[x]);

    qsort((void *)int_list, 5, sizeof(int_list[0]), sort_function);

/*
    Print numbers after sorting
*/
    printf("After sorting ...\n");
    for (x = 0; x < 5; x++)
        printf("%d\n", int_list[x]);
}

© 2004 Jim Valavanis