# std::logical_not

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< cpp‎ | utility‎ | functional

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.
logical_not<void> (C++14) | 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

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

## std::logical_not::operator()

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`.

### 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;
    }

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