# 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 operator< for comparison.

## Declaration

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

### C++98

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

## 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.

## 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>

using namespace std;

int main(void) {
vector<int> v = {1, 2, 3, 4, 5};
bool result;

result = binary_search(v.begin(), v.end(), 3);

if (result == true)
cout << "Element 3 exist in vector." << endl;

v = 10;

result = binary_search(v.begin(), v.end(), 3);

if (result == false)
cout << "Element 3 doesn't exist in vector." << endl;

return 0;
}
```

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

```Element 3 exist in vector.
Element 3 doesn't exist in vector.
```
algorithm.htm