bsearch

Performs a binary search of a sorted array.

void *bsearch( const void *key, const void *base, size_t num, size_t width, int ( __cdecl *compare ) ( const void *elem1, const void *elem2 ) );

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

bsearch returns a pointer to an occurrence of key in the array pointed to by base. If key is not found, the function returns NULL. If the array is not in ascending sort order or contains duplicate records with identical keys, the result is unpredictable.

Parameters

key

Object to search for

base

Pointer to base of search data

num

Number of elements

width

Width of elements

compare

Function that compares two elements: elem1 and elem2

elem1

Pointer to the key for the search

elem2

Pointer to the array element to be compared with the key

Remarks

The bsearch function performs a binary search of a sorted array of num elements, each of width bytes in size. The base value is a pointer to the base of the array to be searched, and key is the value being sought. The compare parameter is a pointer to a user-supplied routine that compares two array elements and returns a value specifying their relationship. bsearch calls the compare routine one or more times during the search, passing pointers to two array elements on each call. The compare routine compares the elements, then returns one of the following values:

Example

/* BSEARCH.C: This program reads the command-line
 * parameters, sorting them with qsort, and then
 * uses bsearch to find the word "cat."
 */

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

int compare( char **arg1, char **arg2 ); /* Declare a function for compare */

void main( int argc, char **argv )
{
   char **result;
   char *key = "cat";
   int i;

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

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

   /* Find the word "cat" using a binary search algorithm: */
   result = (char **)bsearch( (char *) &key, (char *)argv, argc,
                              sizeof( char * ), (int (*)(const void*, const void*))compare );
   if( result )
      printf( "\n%s found at %Fp\n", *result, result );
   else
      printf( "\nCat not found!\n" );
}

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

Output

[C:\work]bsearch dog pig horse cat human rat cow goat
bsearch cat cow dog goat horse human pig rat
cat found at 002D0008

Searching and Sorting Routines

See Also   _lfind, _lsearch, qsort