std:: not1

std::not1 is a helper function to create a function object that returns the complement of the unary predicate function passed. The function object created is of type std:: unary_negate < Predicate > .

The unary predicate type must define a member type, argument_type , that is convertible to the predicate's parameter type. The unary function objects obtained from std::ref , std::cref , std::negate , std::logical_not , std::mem_fn , std::function , std::hash , or from another call to std::not1 have this type defined, as are function objects derived from the deprecated std::unary_function .

Parameters

Return value

std::not1 returns an object of type std:: unary_negate < Predicate > , constructed with pred .

Exceptions

(none)

Example

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
 
struct LessThan7 : std::unary_function<int, bool>
{
    bool operator()(int i) const { return i < 7; }
};
 
int main()
{
    std::vector<int> v(10);
    std::iota(std::begin(v), std::end(v), 0);
 
    std::cout << std::count_if(begin(v), end(v), std::not1(LessThan7())) << '\n';
 
    // the same as above using std::function
    std::function<bool(int)> less_than_9 = [](int x) { return x < 9; };
    std::cout << std::count_if(begin(v), end(v), std::not1(less_than_9)) << '\n';
}

3
1

See also