FIX: Smartptr Property in Interface Causes C2512 Error

• Microsoft Visual C++, 32-bit Editions, version 5.0

SYMPTOMS

The compiler may incorrectly issue error C2512 when a class has a _declspec(property) member. Having a _declspec(property) member is common when you import type-libraries with #import. In addition to error C2512, warnings C4510, C4511, C4512, C4513 and C4610 may also be generated.

RESOLUTION

This can be avoided when doing #import by using the attributes raw_interfaces_only or no_native_types. Unfortunately, this also turns off major functionality.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio 97, Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see the following article in the Microsoft Knowledge Base:

Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

The first sample below causes the compiler to give the following messages when compiled at warning level 4:

warning C4510: 'B' : default constructor could not be generated

warning C4610: struct 'B' can never be instantiated - user defined
constructor required

error C2512: 'B' : no appropriate default constructor available

Sample Code A

   // Compile option needed /W4
   class A
   {  A();
   };
   struct B
   {  __declspec( property (get=getA)) A a;
      A getA();
   };
   void f()
   {
      B b;
   } 

warning C4510: 'IA' : default constructor could not be generated

warning C4511: 'IA' : copy constructor could not be generated

warning C4512: 'IA' : assignment operator could not be generated

warning C4513: 'IA' : destructor could not be generated

warning C4610: struct 'IA' can never be instantiated - user defined constructor required

warning C4510: 'CA' : default constructor could not be generated

warning C4511: 'CA' : copy constructor could not be generated

warning C4512: 'CA' : assignment operator could not be generated

warning C4513: 'CA' : destructor could not be generated

warning C4610: class 'CA' can never be instantiated - user defined constructor required

error C2512: 'CA' : no appropriate default constructor available

Sample Code B

   // custom.idl
   // MIDL options: <none>
   #include <olectl.h>
   #include <idispids.h>
   #ifndef DO_NO_IMPORTS
   import "objidl.idl";
   import "oleidl.idl";
   import "oaidl.idl";
   import "ocidl.idl";
   #endif
   interface IB;
   [ object, uuid(27979FD1-E576-11cf-BFAC-00A02437A6A0) ]
   interface IA : IUnknown
   {
       [propput, id(1)] HRESULT Interface([in] IB* pB);
       [propget, id(1)] HRESULT Interface([out, retval] IB** ppB);
   }
   [ object, uuid(27979FD0-E576-11cf-BFAC-00A02437A6A0) ]
   interface IB : IUnknown
   {
       [id(5)] HRESULT Method([in] int in1);
   }
   [ uuid(596DBF82-2F2D-11D0-A537-00A02437A6A0), version(1.0) ]
   library Custom
   {
       importlib(STDOLE_TLB);
       importlib(STDTYPE_TLB);
       interface IA;
       interface IB;
   }

   // test.cpp
   // compile options: /GX /W4 /c
   #import "Custom.tlb" no_namespace
   class CA : IA
   {
      STDMETHOD_(ULONG, AddRef)() { return 0; }
      STDMETHOD_(ULONG, Release)() { return 0; }
      STDMETHOD(QueryInterface)(REFIID,  LPVOID* ) { return E_NOTIMPL; }
      // ICustom methods
      STDMETHOD(put_Interface)(IB *) { return E_NOTIMPL; }
      STDMETHOD(get_Interface)(IB **) { return E_NOTIMPL; }
   };
   class CB
   {
      CB(){
         CA* pA = new CA;
          if (pA)
            delete pA;
      }
   }; 

Additional query words:

Keywords : kbVS97sp1fix kbVS97sp2fix
Version : 5.0
Platform : NT WINDOWS
Issue type : kbbug