bsearch_s

Article
04/22/2008

Performs a binary search of a sorted array. This is version of bsearch with security enhancements as described in Security Enhancements in the CRT.

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

Parameters

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 argument is the context pointer. The second argument is a pointer to the key for the search. The third argument is a pointer to the array element to be compared with key.
context
A pointer to an object that can be accessed in the comparison function.

Return Value

bsearch_s returns a pointer to an occurrence ofkey 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.

If invalid parameters are passed to the function, the invalid parameter handler is invoked as described in Parameter Validation. If execution is allowed to continue, errnois set to EINVAL and the function returns NULL. For more information, see errno, _doserrno, _sys_errlist, and _sys_nerr.

Error Conditions

key	base	compare	num	width	errno
NULL	any	any	any	any	EINVAL
any	NULL	any	!= 0	any	EINVAL
any	any	any	any	= 0	EINVAL
any	any	NULL	an	any	EINVAL

Remarks

The bsearch_s 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_s calls the compare routine one or more times during the search, passing the context pointer and pointers to two array elements on each call. The compare routine compares the elements, and then returns one of the following values:

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

The context pointer may be useful if the searched data structure is part of an object, and the compare function needs to access members of the object. The compare function may cast the void pointer into the appropriate object type and access members of that object. The addition of the context parameter makes bsearch_s more secure since additional context may be used to avoid reentrancy bugs associated with using static variables to make data available to the compare function.

Requirements

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

For additional compatibility information, see Compatibility in the Introduction.

Example

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

// crt_bsearch_s.cpp
// This program uses bsearch_s to search a string array,
// passing a locale as the context.
// compile with: /EHsc
#include <stdlib.h>
#include <stdio.h>
#include <search.h>
#include <process.h>
#include <locale.h>
#include <locale>
#include <windows.h>
using namespace std;

// The sort order is dependent on the code page.  Use 'chcp' at the
// command line to change the codepage.  When executing this application,
// the command prompt codepage must match the codepage used here:

#define CODEPAGE_850

#ifdef CODEPAGE_850
#define ENGLISH_LOCALE "English_US.850"
#endif

#ifdef CODEPAGE_1252
#define ENGLISH_LOCALE "English_US.1252"
#endif

// The context parameter lets you create a more generic compare.
// Without this parameter, you would have stored the locale in a
// static variable, thus making it vulnerable to thread conflicts
// (if this were a multithreaded program).

int compare( void *pvlocale, char **str1, char **str2)
{
    char *s1 = *str1;
    char *s2 = *str2;

    locale& loc = *( reinterpret_cast< locale * > ( pvlocale));

    return use_facet< collate<char> >(loc).compare(
       s1, s1+strlen(s1),
       s2, s2+strlen(s2) );
}

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

   char *key = "cat";
   char **result;
   int i;

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

   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_s( &key,
                                arr,
                                sizeof(arr)/sizeof(arr[0]),
                                sizeof( char * ),
                                (int (*)(void*, const void*, const void*))compare,
                                &locale(ENGLISH_LOCALE) );
   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

.NET Framework Equivalent

BinarySearch

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