NAME

std::not1 - std::not1

Synopsis

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

not_fn Creates a function object that returns the complement of the
(C++17) result of the function object it holds
(function template)
unary_negate wrapper function object returning the complement of the unary
(deprecated in C++17) predicate it holds
(removed in C++20) (class template)
function wraps callable object of any copy constructible type with
(C++11) specified function call signature
(class template)
move_only_function wraps callable object of any type with specified function call
(C++23) signature
(class template)
not2 constructs custom std::binary_negate object
(deprecated in C++17) (function template)
(removed in C++20)
ptr_fun creates an adaptor-compatible function object wrapper from a
(deprecated in C++11) pointer to function
(removed in C++17) (function template)
unary_function adaptor-compatible unary function base class
(deprecated in C++11) (class template)
(removed in C++17)