std::is_class

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

Checks whether T is a class or struct type. Provides the member constant value which is equal to true, if T is an class or struct type (but not union). Otherwise, value is equal to false.

Template parameters

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 class or struct , 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

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';
}

Output:

true
true
false
false

is_union (C++11)	checks if a type is an union type (class template)
std::experimental::is_class_v (library fundamentals TS)	variable template alias of `std::is_class::value` (variable template)