std::is_void

template< class T >
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.

The behavior of a program that adds specializations for std::is_void or std::is_void_v is undefined.

Template parameters

Helper variable template

template< class T >
inline constexpr bool is_void_v = is_void<T>::value;

Possible implementation

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

Example

#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