C++ Algorithm Functions none_of()

C++ Algorithm none_of() function returns a true value if the value of 'pred' argument is false. The value should be false for all elements in the range [first, last).

Syntax

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

Parameter

first : It specifies the first element in the list.

last: It specifies the last element in the list.

pred: It is an unary function which accepts the argument from the range.

Return value

The function has one return type, 'true'. If the value of argument 'pred' is false for all the elements of the range then the value 'true' is returned, else false.

Example 1

#include <iostream>
#include <algorithm>
#include <array>
int main()
{
	std::array<int, 6> arr= {25,27,29,31,33,35};
	if ( std::none_of(arr.begin(), arr.end(), [](int k) {return k%2==0;} ) )
	std::cout <<"None of the elements is divisible by 2";
	return 0;
}

Output:

 None of the elements is divisible by 2

Example 2

#include<iostream>
#include<algorithm>
using namespace std;
bool abc(int b)
{
	return b<0;
}
int main()
{
	int ar[] = { 2,4,6,8,12,0 };
	int p = sizeof(ar)/sizeof(ar[0]);
	cout<<"Array";
	for(int k=0; k<p; k++)
	cout<<" "<<ar[k];
	if(none_of(ar, ar+p, abc))
	cout<<"None of the elements in the range are negative";
	else
	cout<<"The range has at least one element that is negative";
	return 0;
}

Output:

Array 2 4 6 8 12None of the elements in the range are negative

Complexity

The function moves in a linear way, starting from the first element going towards the last one. For each element of the list value of 'pred' is checked. The search goes on until a mismatch for the 'pred' value is encountered.