std::is_class - cppreference.com (original) (raw)

| | | | | -------------------------------------- | | ------------- | | 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.

Contents

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Possible implementation
  • 3.5 Example
  • 3.6 See also

[edit] Template parameters

[edit] 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

| | true if T is a non-union class type, false otherwise (public static member constant) | | --------------------------------------------------------------------------------------- |

Member functions

| | converts the object to bool, returns value (public member function) | | ---------------------------------------------------------------------- | | | returns value (public member function) |

Member types

[edit] Possible implementation

[edit] Example

#include   struct A {}; static_assert(std::is_class::value);   class B {}; static_assert(std::is_class_v); static_assert(not std::is_class_v<B*>); static_assert(not std::is_class_v<B&>); static_assert(std::is_class_v);   enum class E {}; static_assert(not std::is_class::value);   union U { class UC {}; }; static_assert(not std::is_class_v); static_assert(std::is_class_v<U::UC>);   static_assert(not std::is_class_v);   static_assert(std::is_class_v, "incomplete class"); static_assert(std::is_class_v, "incomplete class");   int main() {}

[edit] See also

| | checks if a type is a union type (class template) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |