std::bsearch

 

C++

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Algorithms library

Iterators library

Numerics library

Input/output library

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Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Algorithm library

Functions
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each countcount_if mismatch equal	findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle  (C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap (C++11) is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <cstdlib>
extern "C" void* bsearch( const void* key, const void* ptr, std::size_t count,                std::size_t size, int (*comp)(const void*, const void*) );
extern "C++" void* bsearch( const void* key, const void* ptr, std::size_t count,                std::size_t size, int (*comp)(const void*, const void*) );

Finds an element equal to element pointed to by key in a sorted array pointed to by ptr. The array contains count elements of size bytes. The elements are compared using function pointed to by comp.

The behavior is undefined if the array is not already sorted in ascending order according to the same criterion that comp uses.

If the array contains several elements that comp would indicate as equal to the element searched for, then it is undefined which element the function will return as the result.

Parameters

key	-	pointer to the element to search for
ptr	-	pointer to the array to examine
count	-	number of element in the array
size	-	size of each element in the array in bytes
comp	-	comparison function which returns ​a negative integer value if the first argument is less than the second, a positive integer value if the first argument is greater than the second and zero if the arguments are equal. key is passed as the first argument, an element from the array as the second. The signature of the comparison function should be equivalent to the following:  int cmp(const void *a, const void *b); The function must not modify the objects passed to it. ​

Return value

Pointer to the found element or NULL if the element has not been found.

Notes

The two overloads provided by the C++ standard library are distinct because the types of the parameter comp are distinct (language linkage is part of its type)

Example

Run this code

#include <cstdlib>
#include <iostream>
 
int compare(const void *ap, const void *bp)
{
    const int *a = (int *) ap;
    const int *b = (int *) bp;
    if(*a < *b)
        return -1;
    else if(*a > *b)
        return 1;
    else
        return 0;
}
 
int main(int argc, char **argv)
{
    const int ARR_SIZE = 8;
    int arr[ARR_SIZE] = { 1, 2, 3, 4, 5, 6, 7, 8 };
 
    int key1 = 4;
    int *p1 = (int *) std::bsearch(&key1, arr, ARR_SIZE, sizeof(arr[0]), compare);
    if(p1)
        std::cout << "value " << key1 << " found at position " << (p1 - arr) << '\n';
     else
        std::cout << "value " << key1 << " not found\n";
 
    int key2 = 9;
    int *p2 = (int *) std::bsearch(&key2, arr, ARR_SIZE, sizeof(arr[0]), compare);
    if(p2)
        std::cout << "value " << key2 << " found at position " << (p2 - arr) << '\n';
     else
        std::cout << "value " << key2 << " not found\n";
}

Output:

value 4 found at position 3
value 9 not found

See also

qsort	sorts a range of elements with unspecified type (function)
equal_range	returns range of elements matching a specific key (function template)
C documentation for bsearch