std::is_class

std::is_class

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

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 > inline 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>

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

See also

is_union (C++11)

checks if a type is an union type (class template)

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