Forward declarations

From: Marcin Kalicinski (kalita_at_poczta.onet.pl)
Date: 05/11/04 

Date: Tue, 11 May 2004 16:35:12 +0200

Hi All,

In some headers meant to work with both C and C++ the following is often
found:

typedef struct tagMyStruct { /*some members*/ } MyStruct;

Can I forward-declare MyStruct somehow?

Or more generally, can I forward declare a typedef or an enum? Also, is
there any reason why there should be difference between forward declarations
of classes and structs (i.e. why I need to explicitly write keyword 'struct'
or 'class' when forward declaring). In some cases I don't immediately know
what to write, because, for example, the type definition in original header
file is generated with some macro, such as this:

STDINTERFACE(IBlahBlah, IBaseBlahBlah) {
    /* Members */
}

Now I need to search for the definition of STDINTERFACE to see how it works.
Even if I find it, it still may silently change in some future version of
the header file, and cause my compilation to fail. Wouldn't allowing a
generic form of forward declaration, without introducing a new keyword:

typename IBlahBlah;

be beneficial to C++?

best regards,
Marcin

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