From cppreference.com
template<classT>structis_class;(since C++11)std::is_class is a
.
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.
Template parameters
T - a type to check Helper variable template
template<classT>constexprboolis_class_v=is_class<T>::value;(since C++17)Inherited from
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_typebooltypestd::integral_constant<bool,value>Possible implementation
namespacedetail{template<classT>std::integral_constant<bool,!std::is_union<T>::value>test(intT::*);template<class>std::false_typetest(...);}template<classT>structis_class:decltype(detail::test<T>(nullptr)){};Example
Run this code
#include<type_traits>structA{};static_assert(std::is_class<A>::value);classB{};static_assert(std::is_class_v<B>);static_assert(notstd::is_class_v<B*>);static_assert(notstd::is_class_v<B&>);static_assert(std::is_class_v<constB>);enumclassE{};static_assert(notstd::is_class<E>::value);unionU{classUC{};};static_assert(notstd::is_class_v<U>);static_assert(std::is_class_v<U::UC>);static_assert(notstd::is_class_v<int>);static_assert(std::is_class_v<structS>,"incomplete class");static_assert(std::is_class_v<classC>,"incomplete class");static_assert(std::is_class_v<decltype([]{})>);intmain(){}See also