qsort

Performs a quick sort.

voidqsort(void*base,size_tnum**,size_twidth,int(__cdecl*compare)(constvoid*elem1,constvoid*elem2));**

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

None

Parameters

base

Start of target array

num

Array size in elements

width

Element size in bytes

compare

Comparison function

elem1

Pointer to the key for the search

elem2

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:

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.

Example

/* QSORT.C: 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 );

void 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

[C:\code]qsort every good boy deserves favor
boy deserves every favor good

Searching and Sorting Routines

See Also   bsearch, _lsearch