std::is_class (3) - Linux Manuals

std::is_class: std::is_class

NAME

std::is_class - std::is_class

Synopsis

Defined in header <type_traits>
template< class T > (since C++11)
struct is_class;

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.

Template parameters

T - a type to check

Helper variable template

template< class T > (since C++17)
inline constexpr bool is_class_v = is_class<T>::value;

Inherited from std::integral_constant

Member constants

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

Member functions

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

operator() returns value
              (public member function)
(C++14)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Possible implementation

  namespace detail {
      template <class T> char test(int T::*);
      struct two { char c[2]; };
      template <class T> two test(...);
  }

  template <class T>
  struct is_class : std::integral_constant<bool, sizeof(detail::test<T>(0))==1
                                              && !std::is_union<T>::value> {};

Example

// Run this code

  #include <iostream>
  #include <type_traits>

  struct A {};

  class B {};

  enum class C {};

  int main()
  {
      std::cout << std::boolalpha;
      std::cout << std::is_class<A>::value << '\n';
      std::cout << std::is_class<B>::value << '\n';
      std::cout << std::is_class<C>::value << '\n';
      std::cout << std::is_class<int>::value << '\n';
  }

Output:

  true
  true
  false
  false