bsearch

Статья
10/16/2008

Performs a binary search of a sorted array. A more secure version of this function is available; see bsearch_s.

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

Параметры

key
Object to search for.
base
Pointer to base of search data.
num
Number of elements.
width
Width of elements.
compare
Callback function that compares two elements. The first is a pointer to the key for the search and the second is a pointer to the array element to be compared with the key.

Возвращаемое значение

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.

Заметки

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:

Value returned by compareroutine	Description
< 0	elem1 less than elem2
0	elem1 equal to elem2
> 0	elem1 greater than elem2

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

Требования

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

For additional compatibility information, see Compatibility in the Introduction.

Пример

This program sorts a string array with qsort, and then uses bsearch to find the word "cat".

// crt_bsearch.c
#include <search.h>
#include <string.h>
#include <stdio.h>

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

int main( void )
{
   char *arr[] = {"dog", "pig", "horse", "cat", "human", "rat", "cow", "goat"};
   char **result;
   char *key = "cat";
   int i;

   /* Sort using Quicksort algorithm: */
   qsort( (void *)arr, sizeof(arr)/sizeof(arr[0]), sizeof( char * ), (int (*)(const 
   void*, const void*))compare );

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

   /* Find the word "cat" using a binary search algorithm: */
   result = (char **)bsearch( (char *) &key, (char *)arr, sizeof(arr)/sizeof(arr[0]),
                              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" );
}

cat cow dog goat horse human pig rat
cat found at 002F0F04