`bsearch`

Article
12/02/2022

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

Syntax

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

Parameters

key
Pointer to the key to search for.

base
Pointer to the base of the search data.

number
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.

Return value

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

Remarks

The bsearch function performs a binary search of a sorted array of number 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 the requested key to an array element. It returns one of the following values that specify their relationship:

Value returned by `compare` routine	Description
`< 0`	Key is less than array element.
`0`	Key is equal to array element.
`> 0`	Key is greater than array element.

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

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

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

For more compatibility information, see Compatibility.

Example

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