Std :: is_class implementation

Question

I was wondering how actually std::is_class( http://www.cplusplus.com/reference/type_traits/is_class/ ). I looked at /usr/include/++/4.8/tr1/type_traits , but it seems that the only thing there is:

/// is_class
template<typename _Tp>
  struct is_class
  : public integral_constant<bool, __is_class(_Tp)>
  { };

and the definition __is_classcannot be found anywhere (or I just did not look deep enough). Anyway, I would be happy if someone could tell me where to look for this (as well as another is_***from the namespace std)

Answer 1

__is_classis a C ++ extension provided by the gcc compiler. See gcc type specifications .

++ , ( ).