std::not1

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not1
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Defined in header <functional>
template< class Predicate >
std::unary_negate<Predicate> not1(const Predicate& pred);
 (until C++14)
template< class Predicate >
constexpr std::unary_negate<Predicate> not1(const Predicate& pred);
 (since C++14)
(deprecated in C++17)
(removed in C++20)

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

pred - unary predicate

Return value

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

Exceptions

None.

Example

Run this code
#include <algorithm>
#include <numeric>
#include <iterator>
#include <functional>
#include <iostream>
#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";
}

Output: 

3
1

See also

(C++17)
 Creates a function object that returns the complement of the result of the function object it holds
(function template)
(deprecated in C++17)(removed in C++20)
 wrapper function object returning the complement of the unary predicate it holds
(class template)
(C++11)
 wraps callable object of any copy constructible type with specified function call signature
(class template)
(C++23)
 wraps callable object of any type with specified function call signature
(class template)
(deprecated in C++17)(removed in C++20)
 constructs custom std::binary_negate object
(function template)
(deprecated in C++11)(removed in C++17)
 creates an adaptor-compatible function object wrapper from a pointer to function
(function template)
(deprecated in C++11)(removed in C++17)
 adaptor-compatible unary function base class
(class template)
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