NAME¶

std::is_void - std::is_void

Synopsis¶

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

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

Inherited from std::integral_constant

Member constants¶

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

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (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 checks if a type is an array type
(C++11) (class template)
is_pointer checks if a type is a pointer type
(C++11) (class template)
is_enum checks if a type is an enumeration type
(C++11) (class template)
is_union checks if a type is a union type
(C++11) (class template)
is_class checks if a type is a non-union class type
(C++11) (class template)
is_function checks if a type is a function type
(C++11) (class template)
is_object checks if a type is an object type
(C++11) (class template)