NAME

std::unary_negate - std::unary_negate

Synopsis

Defined in header <functional>
template< class Predicate >
struct unary_negate : public (until C++11)
std::unary_function<Predicate::argument_type, bool>;
(since C++11)
template< class Predicate > (deprecated in
struct unary_negate; C++17)
(removed in C++20)

unary_negate is a wrapper function object returning the complement of the unary
predicate it holds.

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.

unary_negate objects are easily constructed with helper function std::not1.

Member types

Type Definition
argument_type Predicate::argument_type
result_type bool

Member functions

constructor constructs a new unary_negate object with the supplied predicate
(public member function)
returns the logical complement of the result of a call to the stored
operator() predicate
(public member function)

std::unary_negate::unary_negate

explicit unary_negate( Predicate const& pred ); (until C++14)
explicit constexpr unary_negate( Predicate const& pred ); (since C++14)

Constructs a unary_negate function object with the stored predicate pred.

Parameters

pred - predicate function object

std::unary_negate::operator()

bool operator()( argument_type const& x ) const; (until C++14)
constexpr bool operator()( argument_type const& x ) const; (since C++14)

Returns the logical complement of the result of calling pred(x).

Parameters

x - argument to pass through to predicate

Return value

The logical complement of the result of calling pred(x).

Example

// Run this code

#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::unary_negate<less_than_7> not_less_than_7((less_than_7()));

std::cout << std::count_if(v.begin(), v.end(), not_less_than_7);

/* C++11 solution:
// Use std::function<bool (int)>
std::function<bool (int)> not_less_than_7 =
[](int x)->bool{ return !less_than_7()(x); };

std::cout << std::count_if(v.begin(), v.end(), not_less_than_7);
*/
}

Output:

3

See also

binary_negate wrapper function object returning the complement of the binary
(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)
not1 constructs custom std::unary_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)