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.


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 argument 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

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


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

Returns the logical NOT of arg.


arg - value to compute logical NOT of

Return value

The result of !arg.


May throw implementation-defined exceptions.

Possible implementation

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

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