# C++ Algorithm Library - binary_search() Function

## Description

The C++ function std::algorithm::binary_search() tests whether value exists in sorted sequence or not. It use comp function for comparison.

## Declaration

Following is the declaration for std::algorithm::binary_search() function form std::algorithm header.

### C++98

```template <class ForwardIterator, class T, class Compare>
bool binary_search (ForwardIterator first, ForwardIterator last,
const T& val, Compare comp);
```

## Parameters

• first − Forward iterators to the initial positions of the searched sequence.

• last − Forward iterators to the final positions of the searched sequence.

• val − Value to search for in the range.

• comp − Binary function that accepts two arguments and returns a bool.

## Return value

Returns true if value exists otherwise false.

## Exceptions

Throws exception if either element comparison or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

## Time complexity

Logarithmic in the distance between first and last.

## Example

The following example shows the usage of std::algorithm::binary_search() function.

```#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

using namespace std;

bool comp(string s1, string s2) {
return (s1 == s2);
}

int main(void) {
vector<string> v = {"ONE", "Two", "Three"};
bool result;

result = binary_search(v.begin(), v.end(), "one", comp);

if (result == true)
cout << "String \"one\" exist in vector." << endl;

v = "Ten";

return 0;
}
```

Let us compile and run the above program, this will produce the following result −

```String "one" exist in vector.
```
algorithm.htm