# std::is_void

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< cpp‎ | types

Defined in header `<type_traits>` |  |
template< class T > struct is_void; |  | (since C++11)

`std::is_void` is a UnaryTypeTrait.

Checks whether `T` is a void type. Provides the member constant value that is equal to true, if `T` is the type void, const void, volatile void, or const volatile void. Otherwise, value is equal to false.

If the program adds specializations for `std::is_void` or `std::is_void_v`, the behavior is undefined.

### Template parameters

T | - | a type to check

### Helper variable template

template< class T > constexpr bool is_void_v = is_void<T>::value; |  | (since C++17)

## Inherited from std::integral_constant

### Member constants

value [static] | true if `T` is the type void (possibly cv-qualified), false otherwise (public static member constant)

### Member functions

operator bool | converts the object to bool, returns value (public member function)
operator() (C++14) | returns value (public member function)

### Member types

Type | Definition
`value_type` | bool
`type` | std::integral_constant <bool, value>

### Possible implementation

    template<class T>
    struct is_void : std::is_same<void, typename std::remove_cv<T>::type> {};

### Example

Run this code

    #include <type_traits>

    void foo();

    static_assert
    (
        std::is_void_v<void> == true and
        std::is_void_v<const void> == true and
        std::is_void_v<volatile void> == true and
        std::is_void_v<void*> == false and
        std::is_void_v<int> == false and
        std::is_void_v<decltype(foo)> == false and
        std::is_void_v<std::is_void<void>> == false
    );

    int main() {}

### See also

is_array (C++11) | checks if a type is an array type (class template)
is_pointer (C++11) | checks if a type is a pointer type (class template)
is_enum (C++11) | checks if a type is an enumeration type (class template)
is_union (C++11) | checks if a type is a union type (class template)
is_class (C++11) | checks if a type is a non-union class type (class template)
is_function (C++11) | checks if a type is a function type (class template)
is_object (C++11) | checks if a type is an object type (class template)

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