std::is_class
From cppreference.com
| Defined in header <type_traits>
|
||
template< class T > struct is_class; |
(since C++11) | |
std::is_class is a UnaryTypeTrait.
Checks whether T is a non-union class type. Provides the member constant value which is equal to true, if T is a class type (but not union). Otherwise, value is equal to false.
If the program adds specializations for std::is_class or std::is_class_v, the behavior is undefined.
Template parameters
| T | - | a type to check |
Helper variable template
template< class T > constexpr bool is_class_v = is_class<T>::value; |
(since C++17) | |
Inherited from std::integral_constant
Member constants
value [static] |
true if T is a non-union class type, 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>
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Possible implementation
namespace detail
{
template<class T>
std::integral_constant<bool, !std::is_union<T>::value> test(int T::*);
template<class>
std::false_type test(...);
}
template<class T>
struct is_class : decltype(detail::test<T>(nullptr)) {};
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Example
Run this code
#include <type_traits>
struct A {};
static_assert(std::is_class<A>::value);
class B {};
static_assert(std::is_class_v<B>);
static_assert(not std::is_class_v<B*>);
static_assert(not std::is_class_v<B&>);
static_assert(std::is_class_v<const B>);
enum class E {};
static_assert(not std::is_class<E>::value);
union U { class UC {}; };
static_assert(not std::is_class_v<U>);
static_assert(std::is_class_v<U::UC>);
static_assert(not std::is_class_v<int>);
static_assert(std::is_class_v<struct S>, "incomplete class");
static_assert(std::is_class_v<class C>, "incomplete class");
int main() {}
See also
(C++11) |
checks if a type is a union type (class template) |