qsort

Performs a quick sort. A more secure version of this function is available; see qsort_s.

Syntax

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

Parameters

base
Start of target array.

number
Array size in elements.

width
Element size in bytes.

compare
Pointer to a user-supplied routine that compares two array elements and returns a value that specifies their relationship.

Remarks

The qsort function implements a quick-sort algorithm to sort an array of number elements, each of width bytes. The argument base is a pointer to the base of the array to be sorted. qsort overwrites this array by using the sorted elements.

qsort calls the compare routine one or more times during the sort, and passes pointers to two array elements on each call.

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

The routine compares the elements and returns one of the following values.

Compare function 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.

This function validates its parameters. If compare or number is NULL, or if base is NULL and number is nonzero, or if width is less than zero, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, the function returns and errno is set to EINVAL.

Requirements

Routine Required header
qsort <stdlib.h> and <search.h>

For additional compatibility information, see Compatibility.

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 );
}
boy deserves every favor good

See also

Searching and Sorting
bsearch
_lsearch