std::binary_search() in C++ STL (original) (raw)

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 header and works with arrays and STL containers such as vector and set.

C++ `

#include <bits/stdc++.h> using namespace std; int main() { vector 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;

}

`

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 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;

}

`

**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 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;

}

`

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