Question

I’ve been told that every COM method callable from C++ code (take for instance IHTMLDocument2::write) has an equivalent C declaration, usable from C code…

How do I find it?

Thanks in advance!

Answer 1

This particular interface is documented as being provided by <mshtml.h>. Now, as it happens the second and third line of that file are:

// Include the full header file that works for C
#include "mshtmlc.h"

Looking into that file, we find the declaration

    /* [id][vararg] */ HRESULT ( STDMETHODCALLTYPE *write )( 
        IHTMLDocument2 * This,
        /* [in] */ __RPC__in SAFEARRAY * psarray);

Note that this is actually a pointer to the IHTMLDocument2::write method.

Sometimes the C declaration is the same header; sometimes the declaration isn’t publicly available. But the COM standard is an ABI (a binary interface) designed such that you can always write a C declaration. Could be painful though.