Message map and virtual inheritance causes C4407 warning

=?windows-1252?Q?=22Fernando_A._G=F3mez_F.=22?= <>
Mon, 02 Mar 2009 01:35:02 -0600
Hello all. I have the following code:

class IMessageProvider;

class IMessageProcessor {
     virtual void UpdateMessages(IMessageProvider* pProvider) = 0;

class CCatalogDocument :
   public CDocument, public virtual IMessageProcessor

     virtual void UpdateMessages(IMessageProvider* pProvider);
     void OnCommandSave();

BEGIN_MESSAGE_MAP(CCatalogDocument, CDocument)
   ON_COMMAND(ID_CATALOG_SAVE, OnCommandSave) // C4407

When I compile this code, I get the C4407 warning:
Cast between different pointer to member representations, compiler may
generate incorrect code.

The MSDN documentation says that:
C4407 can be generated because of compiler conformance work that was
done in Visual C++ 2005; pointer-to-members now require qualified name
and &. [...] C4407 can occur if you cast between a multiple inheritance
pointer-to-member to a single inheritance pointer-to-member. Sometimes
this can work, but sometimes it can?t because the single inheritance
pointer-to-member representation doesn?t hold sufficient information.
[...] You can also try rearranging your base classes; the compiler is
detecting a loss of information in the conversion because a base class
is at a non-zero offset from the derived.

So my only chance, as I understand it, is not to inherit virtually from
IMessageProcessor (when I remove the "virtual", the warning is gone).
However, I'd like to keep it virtual, since CCatalogDocument-derived
classes can inherit from IMessageProcessor-derived interfaces.

So I was wondering whether I can safely ignore this warning or not. Any
help or comments regarding this issue will be really appreciated.

Thanks in advance.

Fernando G?mez

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