Q168009: FIX: Smartptr Property in Interface Causes C2512 Error

Article: Q168009
Product(s): Microsoft C Compiler
Version(s): 5.0
Operating System(s): 
Keyword(s): kbVS97sp1fix kbVS97sp2fix
Last Modified: 17-JUL-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
- Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
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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;
     }

The second sample generates the following errors:

  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 
Technology        : kbVCsearch kbAudDeveloper kbVC500 kbVC32bitSearch kbVC500Search
Version           : 5.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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