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std:: logical_not

From cppreference.net
C++
Utilities library
Function objects
Function invocation
(C++17) (C++23)
Identity function object
(C++20)
Old binders and adaptors
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Defined in header <functional>
template < class T >
struct logical_not ;
(until C++14)
template < class T = void >
struct logical_not ;
(since C++14)

Function object for performing logical NOT (logical negation). Effectively calls operator ! for type T .

Contents

Specializations

The standard library provides a specialization of std::logical_not when T is not specified, which leaves the parameter types and return type to be deduced.

(C++14)
function object implementing ! x deducing parameter and return types
(class template specialization)
(since C++14)

Member types

Type Definition
result_type (deprecated in C++17) (removed in C++20) bool
argument_type (deprecated in C++17) (removed in C++20) T

These member types are obtained via publicly inheriting std:: unary_function < T, bool > .

(until C++11)

Member functions

operator()
returns the logical NOT of the argument
(public member function)

std::logical_not:: operator()

bool operator ( ) ( const T & arg ) const ;
(constexpr since C++14)

Returns the logical NOT of arg .

Parameters

arg - value to compute logical NOT of

Return value

The result of ! arg .

Exceptions

May throw implementation-defined exceptions.

Possible implementation 

constexpr // since C++14
bool operator()(const T& arg) const 
{
    return !arg;
}