< cpp‎ | algorithm
Revision as of 22:43, 31 May 2013 by P12bot (Talk | contribs)

Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations

Numeric operations
C library
Defined in header <algorithm>
template< class ForwardIt, class T >
bool binary_search( ForwardIt first, ForwardIt last, const T& value );
template< class ForwardIt, class T, class Compare >
bool binary_search( ForwardIt first, ForwardIt last, const T& value, Compare comp );

Checks if the sorted range [first, last) contains an element equal to value. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.



first, last - the range of elements to examine
value - value to compare the elements to
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type T can be implicitly converted to both Type1 and Type2, and an object of type ForwardIt can be dereferenced and then implicitly converted to both Type1 and Type2. ​

Type requirements
ForwardIt must meet the requirements of ForwardIterator.

Return value

true if an element equal to value is found, false otherwise.


The number of comparisons performed is logarithmic in the distance between first and last

Possible implementation

First version
template<class ForwardIt, class T>
bool binary_search(ForwardIt first, ForwardIt last, const T& value)
    first = std::lower_bound(first, last, value);
    return (!(first == last) && !(value < *first));
Second version
template<class ForwardIt, class T, class Compare>
bool binary_search(ForwardIt first, ForwardIt last, const T& value, Compare comp)
    first = std::lower_bound(first, last, value, comp);
    return (!(first == last) && !(comp(value, *first));


#include <iostream>
#include <algorithm>
#include <vector>
int main()
    std::vector<int> haystack {1, 3, 4, 5, 9};
    std::vector<int> needles {1, 2, 3};
    for (auto needle : needles) {
        std::cout << "Searching for " << needle << '\n';
        if (std::binary_search(haystack.begin(), haystack.end(), needle)) {
            std::cout << "Found " << needle << '\n';
        } else {
            std::cout << "no dice!\n";


Searching for 1
Found 1
Searching for 2
no dice!
Searching for 3
Found 3

See also

returns range of elements matching a specific key
(function template) [edit]