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Compiler Error C2788

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'identifier' : more than one GUID associated with this object

The __uuidof operator takes a user-defined type with a GUID attached or an object of such a user-defined type. This error occurs when the argument is an object with multiple GUIDs.

The following sample generates C2788:

// C2788.cpp
#include <windows.h>
struct __declspec(uuid("00000001-0000-0000-0000-000000000000")) A {};
struct __declspec(uuid("{00000002-0000-0000-0000-000000000000}")) B {};
template <class T, class U> class MyClass {};

typedef MyClass<A,B> MyBadClass;
typedef MyClass<A,A> MyGoodClass;

int main() {
   __uuidof(MyBadClass);    // C2788
   // try the following line instead
   __uuidof(MyGoodClass);
}