.NET and COM Interoperability Handbook, The

Rich Error Information

Most COM programmers know that COM objects return a data structure called an HRESULT to indicate the status of a method call. If the method is successful, the COM object should return S_OK. If the method fails, the COM object can return any number of pre-defined HRESULTS, such as E_FAIL or E_INVALIDARG, or you can use the MAKE_HRESULT macro to create your own error HRESULTs. Although just returning an HRESULT is sufficient in some cases, in many cases, a client will want a textual description of the error, the name of the method that was the source of the error, and perhaps even a link to a help file that contains additional information about the error. A COM object can return this sort of rich error information to a client ...