Exceptions and Errors
Well-behaved COM server objects don't usually throw exceptions back to their clients, but they can. So, to be cautious it's a good idea to put most of your COM-related code in a try block and follow it with a catch block for COM errors. COM errors are encapsulated in the Visual C++ compiler helper class _com_error.
Other than that, you need to know about HRESULT. This is a 32-bit data structure used to return status information about calls to methods in the COM APIs. You can't just check on a nonzero return value to see whether or not a call failed; it is a more complex data structure than that. Visual C++ provides some macros to check on HRESULT. I use FAILED and SUCCEEDED. Both return booleans. You'll see that the book's ...
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