std:: 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

Helper variable template

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