# C++ Algorithm Library - all_of() Function

## Description

The C++ function std::algorithm::all_of() Returns true if predicate returns true for all the elements in the range of first to last. If range is empty then also true is returned otherwise it returns false.

## Declaration

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

### C++11

```template <class InputIterator, class UnaryPredicate>
bool all_of (InputIterator first, InputIterator last, UnaryPredicate pred);
```

## Parameters

• first − Input iterators to the initial positions in a sequence.

• last − Input iterators to the final positions in a sequence.

• pred − An unary predicate function that accepts an element and returns a bool.

## Return value

Returns true if predicate returns true for all the elements in the range or if the range is empty otherwise returns false.

## Exceptions

Throws exception if either predicate or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

## Time complexity

Linear in the distance between first and last.

## Example

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

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

using namespace std;

bool is_even(int n) {
return (n % 2 == 0);
}

int main(void) {
vector<int> v = {2, 4, 6, 8, 10};
bool result;

result = all_of(v.begin(), v.end(), is_even);

if (result == true)
cout << "Vector contains all even numbers." << endl;

v = 1;

result = all_of(v.begin(), v.end(), is_even);

if (result == false)
cout << "Vector doesn't contain all even numbers." << endl;

return 0;
}
```

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

```Vector contains all even numbers.
Vector doesn't contain all even numbers.
```
algorithm.htm