c++ - Which COM smart pointer classes to use?

Question

I'm confused by the choices for COM smart pointers classes for C++ programming:

There's three four I'm aware of:

• CCOMPtr from ATL
• _com_ptr_t from the MS Com Support Classes
• TComInterface (because I'm using C++Builder 2009)
• CCOMQIPtr, (which I'd previously forgotten)

I've read about the error vs. exception handling differences of the first two, but TComInterface seems totally undocumented. Both the first two seem to have gotchas or 'unexpected' behaviour, from what I can find.

Ideally, I'd like something that's clean and modern C++, but boost::com doesn't exist as far as I know...

I need to control an application from another vendor. They provide a COM interface via a TLB file.

Answer 1

If you are using the type-library import stuff, it will generate code based upon _com_ptr_t and the related COM Support Classes. Go ahead and use those if you are just using stuff from those libraries.

If you are writing ATL-based code, then use CCOMPtr and the other ATL-based classes.

Things may get ugly if you need to mix-and-match both types, but you should probably just get comfortable with both and use whichever makes the most sense for whatever you are doing at the time.

The nice thing is that you have the source for all of these things, so you don't have to rely only on the documentation (which has not been getting much care since .NET appeared).