std::binary_search() in C++ STL

Last Updated : 20 Jan, 2026

std::binary_search() is a C++ STL algorithm used to efficiently check whether a specific value exists in a sorted range. It is defined in the <algorithm> header and works with arrays and STL containers such as vector and set.

C++ 
#include <bits/stdc++.h>
using namespace std;
int main() {
    vector<int> v = {1, 3, 6, 8, 9};
    int k = 8;

    if (binary_search(v.begin(), v.end(), k))
        cout << k << " is Present";
    else
        cout << k << " is NOT Present";

    return 0;
}

Output
8 is Present

Syntax

std::binary_search(first, last, k, comp);

Parameters

  • first: Iterator to the first element of the range.
  • last: Iterator to the theoretical element just after the last element of range.
  • k: The value to be search.
  • comp: Custom comparison function that defines the ordering of elements. By default, std::less<T> is used.

Return Value

  • Returns true, if k is present in the given range.
  • Returns false, if k is not present in the given range.

Note: Behaviour of binary_search() is undefined if the given range is not sorted as binary search algorithm can only be implemented on sorted data.

The following examples demonstrates the different use cases of std::binary_seach() function:

Example 1: Checking if an Element Exists in Array using std::binary_search()

C++ 
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {1, 4, 5, 7, 9};
    int n = sizeof(arr) / sizeof(arr[0]);
    int k = 7;

    // Check if the element exists
    if (binary_search(arr, arr + n, k))
        cout << k << " is Present";
    else
        cout << k << " is NOT Present";
    return 0;
}

Output
7 is Present

Explanation: This program uses std::binary_search() to check whether the value 7 exists in a sorted integer array and prints whether it is present or not.

Example 2: Using binary_search() on a Set Container

C++ 
#include <bits/stdc++.h>
using namespace std;

int main() {
    set<int> s = {1, 4, 5, 7, 9};
    int k = 8;

    // Check if the element exists
    if (binary_search(s.begin(), s.end(), k))
        cout << k << " is Present";
    else
        cout << k << " is NOT Present";
    return 0;
}

Output
8 is NOT Present

Explanation: Even though set container does not have random access, binary_search() function still works because of the reason discussed below.

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