Defined in header
<type_traits> | ||
---|---|---|
template< class T > struct is_class; | (since C++11) |
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".
T | - | a type to check |
template< class T > constexpr bool is_class_v = is_class<T>::value; | (since C++17) |
value
[static]
| true if T is a class or struct , false otherwise (public static member constant) |
operator bool | converts the object to bool , returns value (public member function) |
operator()
(C++14)
| returns value (public member function) |
Type | Definition |
---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
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> {}; |
#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
(C++11)
| checks if a type is an union type (class template) |
(library fundamentals TS)
| variable template alias of std::is_class::value (variable template) |
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