std::is_void
From cppreference.com
| 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
(C++11) |
checks if a type is an array type (class template) |
(C++11) |
checks if a type is a pointer type (class template) |
(C++11) |
checks if a type is an enumeration type (class template) |
(C++11) |
checks if a type is a union type (class template) |
(C++11) |
checks if a type is a non-union class type (class template) |
(C++11) |
checks if a type is a function type (class template) |
(C++11) |
checks if a type is an object type (class template) |