std::logical_not - cppreference.com

From cppreference.com

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.

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.

function object implementing !x deducing parameter and return types
(class template specialization) [edit]

(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

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;
}