std::is_class

template< class T >
struct is_class;

Checks whether T is a 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.

Note that types declared with the struct keyword are classes, so this trait is true for "structs".

Template parameters

Helper variable template

template< class T >
constexpr bool is_class_v = is_class<T>::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

#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';
}

true
true
false
false

See also