std::not1

From Cppreference

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. Unary function objects derived from std::unary_function will have this type defined, as will functions wrapped in a call to std::ptr_fun. In C++11, a std::function specialization for unary functions provides this type.

[edit] Parameters

[edit] Return value

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

[edit] Exceptions

None.

[edit] Example

#include <algorithm>
#include <functional>
#include <iostream>
#include <vector>
 
struct less_than_7 : std::unary_function<int, bool>
{
    bool operator()(int i) const { return i < 7; }
};
 
int main()
{
    std::vector<int> v;
    for (int i = 0; i < 10; ++i) v.push_back(i);
 
    std::cout << std::count_if(v.begin(), v.end(), std::not1(less_than_7()));
 
    /* C++11 solution:
        // Use std::function<bool (int)> to create or wrap the predicate type
        std::function<bool (int)> less_than_7 = [](int x){ return x < 7; };
 
        std::cout << std::count_if(v.begin(), v.end(), std::not1(less_than_7));
    */
}

Output:

3

[edit] See also