Performs a binary search of a sorted array.
| #include <stdlib.h> | Required for ANSI compatibility | |
| #include <search.h> | Required only for function declarations |
void *bsearch( const void *key, const void *base, size_t num, size_t width,
int ( __cdecl *compare )( const void *elem1, const void *elem2 ) );
| 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 |
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 argument is a pointer to a user-supplied routine that compares two array elements and returns a value specifying their relationship. The bsearch function calls the compare routine one or more times during the search, passing pointers to two array elements on each call. The routine compares the elements, then returns one of the following values:
| Value | Meaning |
| < 0 | elem1 less than elem2 |
| = 0 | elem1 identical to elem2 |
| > 0 | elem1 greater than elem2 |
If the array you are searching is not in ascending sort order, bsearch does not work properly. If the array contains duplicate records with identical keys, there is no way to predict which of the duplicate records will be located by bsearch.
The bsearch function returns a pointer to an occurrence of key in the array pointed to by base. If key is not found, the function returns NULL.
Standards:ANSI, UNIX
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:DOS32X
/* BSEARCH.C: This program reads the command-line arguments, 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( (char *)argv, argc, sizeof( char * ), 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 * ), 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 );
}
[C:\LIBREF] bsearch dog pig horse cat human rat cow goat
bsearch cat cow dog goat horse human pig rat
cat found at 0292:0FD0