How to write `is_complete` template?

It might be a bit late, but so far, no C++ 11 solution worked for both complete and abstract types.

So, here you are.

With VS2015 (v140), g++ >= 4.8.1, clang >= 3.4, this is working:

template <class T, class = void>
struct IsComplete : std::false_type
{};

template <class T>
struct IsComplete< T, decltype(void(sizeof(T))) > : std::true_type
{};

Thanks to Bat-Ulzii Luvsanbat: https://blogs.msdn.microsoft.com/vcblog/2015/12/02/partial-support-for-expression-sfinae-in-vs-2015-update-1/

With VS2013 (V120):

namespace Details
{

    template <class T>
    struct IsComplete
    {
        typedef char no;
        struct yes { char dummy[2]; };

        template <class U, class = decltype(sizeof(std::declval< U >())) >
        static yes check(U*);

        template <class U>
        static no check(...);

        static const bool value = sizeof(check< T >(nullptr)) == sizeof(yes);
    };

} // namespace Details


template <class T>
struct IsComplete : std::integral_constant< bool, Details::IsComplete< T >::value >
{};

This one is inspired from the internets and static assert that template typename T is NOT complete?

template<class T>
struct is_complete {
    static T & getT();
    static char (& pass(T))[2];
    static char pass(...);

    static const bool value = sizeof(pass(getT()))==2;
};

The answer given by Alexey Malistov can be used on MSVC with a minor modification:

namespace 
{
    template<class T, int discriminator>
    struct is_complete {  
      static T & getT();   
      static char (& pass(T))[2]; 
      static char pass(...);   
      static const bool value = sizeof(pass(getT()))==2;
    };
}
#define IS_COMPLETE(X) is_complete<X,__COUNTER__>::value

Unfortunately, the __COUNTER__ predefined macro is not part of the standard, so it would not work on every compiler.