std::not1

template< class Predicate >
std::unary_negate<Predicate> not1( const Predicate& pred );

template< class Predicate >
constexpr std::unary_negate<Predicate> not1( const Predicate& pred );

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(begin(v), end(v), 0);
 
    std::cout << std::count_if(begin(v), end(v), std::not1(LessThan7())) << '\n';
 
    //same as above, but 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';
}

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See also