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qsort
Performs a quick sort.
void qsort( void *base, size_t num, size_t width, int (__cdecl *compare )(const void *elem1, const void *elem2 ) );
Routine Required Header Compatibility
qsort <stdlib.h> and <search.h> ANSI, Win 95, Win NT
For additional compatibility information, see Compatibility in the Introduction.
Libraries
LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version
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:
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.
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
