Header File 

stdlib.h 

Category 

Memory and String Manipulation Routines 

Prototype 

void qsort(void *base, size_t nelem, size_t width, int (_USERENTRY *fcmp)(const void *, const void *)); 

Description 

Sorts using the quicksort algorithm. 

qsort is an implementation of the “median of three” variant of the quicksort algorithm. qsort sorts the entries in a table by repeatedly calling the user-defined comparison function pointed to by fcmp.

• base points to the base (0th element) of the table to be sorted.
• nelem is the number of entries in the table.
• width is the size of each entry in the table, in bytes.

• fcmp accepts two arguments, elem1 and elem2, each a pointer to an entry in the table. The comparison function compares each of the pointed-to items (*elem1 and *elem2), and returns an integer based on the result of the comparison.
• *elem1 < *elem2 fcmp returns an integer < 0
• *elem1 == *elem2 fcmp returns 0
• *elem1 > *elem2 fcmp returns an integer > 0

Return Value 

None. 

Example  

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int sort_function( const void *a, const void *b);
char list[5][4] = { "cat", "car", "cab", "cap", "can" };
int main(void)
{
   int  x;
   qsort((void *)list, 5, sizeof(list[0]), sort_function);
   for (x = 0; x < 5; x++)
      printf("%s\n", list[x]);
   return 0;
}
int sort_function( const void *a, const void *b)
{
   return( strcmp((char *)a,(char *)b) );
}

Portability