3 out of 5 rated this helpful - Rate this topic

qsort

Visual Studio .NET 2003

Performs a quick sort.

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

Parameters

base: Start of target array.
num: Array size in elements.
width: Element size in bytes.
compare: Comparison function. The first parameter is a pointer to the key for the search and the second parameter is a pointer to the array element to be compared with the key.

Remarks

The qsort function implements a quick-sort algorithm to sort an array of num elements, each of width bytes. The argument base is a pointer to the base of the array to be sorted. qsort overwrites this array with the sorted elements. The argument compare is a pointer to a user-supplied routine that compares two array elements and returns a value specifying their relationship. qsort calls the compare routine one or more times during the sort, passing pointers to two array elements on each call:

compare( (void *) elem1, (void *) elem2 );

The routine must compare the elements, then return one of the following values:

Return value	Description
< 0	elem1 less than elem2
0	elem1 equivalent to elem2
> 0	elem1 greater than elem2

The array is sorted in increasing order, as defined by the comparison function. To sort an array in decreasing order, reverse the sense of "greater than" and "less than" in the comparison function.

Requirements

Routine	Required header	Compatibility
qsort	<stdlib.h> and <search.h>	ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

Example

// crt_qsort.c
// arguments: every good boy deserves favor

/* This program reads the command-line
 * parameters and uses qsort to sort them. It
 * then displays the sorted arguments.
 */

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

int compare( const void *arg1, const void *arg2 );

int main( int argc, char **argv )
{
   int i;
   /* Eliminate argv[0] from sort: */
   argv++;
   argc--;

   /* Sort remaining args using Quicksort algorithm: */
   qsort( (void *)argv, (size_t)argc, sizeof( char * ), compare );

   /* Output sorted list: */
   for( i = 0; i < argc; ++i )
      printf( " %s", argv[i] );
   printf( "\n" );
}

int compare( const void *arg1, const void *arg2 )
{
   /* Compare all of both strings: */
   return _stricmp( * ( char** ) arg1, * ( char** ) arg2 );
}

Output