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[0] = 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.