std::unary_negate

 

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unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*) mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

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

std::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.

std::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)
operator()	returns the logical complement of the result of a call to the stored predicate (public member function)

std::unary_negate::unary_negate

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

Constructs a std::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(7, 7);
    v[0] = v[1] = v[2] = 6;
 
    std::unary_negate<less_than_7> not_less_than_7((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:

4

See also

binary_negate (deprecated in C++17)(removed in C++20)	wrapper function object returning the complement of the binary predicate it holds (class template)
function (C++11)	wraps callable object of any copy constructible type with specified function call signature (class template)
move_only_function (C++23)	wraps callable object of any type with specified function call signature (class template)
not1 (deprecated in C++17)(removed in C++20)	constructs custom std::unary_negate object (function template)
ptr_fun (deprecated in C++11)(removed in C++17)	creates an adaptor-compatible function object wrapper from a pointer to function (function template)
unary_function (deprecated in C++11)(removed in C++17)	adaptor-compatible unary function base class (class template)