Re: unexpected exception handler

From:
=?Utf-8?B?R2Vvcmdl?= <George@discussions.microsoft.com>
Newsgroups:
microsoft.public.vc.language
Date:
Sat, 19 Jan 2008 05:16:00 -0800
Message-ID:
<2252CBE4-E2C7-4B3C-B4E2-D0DF2D63E193@microsoft.com>
Thanks Tamas,

     HRESULT _hr = raw_MyMethod(my_param);
     if (FAILED(_hr)) _com_issue_errorex(_hr, this, __uuidof(this));


1. For the wrapper code, I think there may be exceptions from raw_MyMethod?

2. Does _com_issue_errorex(_hr, this, __uuidof(this)); translate a failed
_hr into an exception?

regards,
George

"Tamas Demjen" wrote:

George wrote:

I always use HRESULT from COM API, like CoCreateInstance or something. What
do you mean "COM Exception"?


I brought up the COM exception topic first, sorry if I confused you. I
wasn't specific enough. What I meant was that when you #import a type
library file, the compiler automatically generates a C++ wrapper for
you, something like this (as of VC++ 2005):

inline HRESULT IMyClass::MyMethod ( long my_param) {
     HRESULT _hr = raw_MyMethod(my_param);
     if (FAILED(_hr)) _com_issue_errorex(_hr, this, __uuidof(this));
     return _hr;
}

You can catch such errors the following way:

try
{
    my_interface->MyMethod(my_param);
}
catch(_com_error& ce)
{
}

As you can see, this happens in the C++ wrapper, and not on the COM
level. Technically the 3rd party code returns HRESULT, and it only turns
into C++ exceptions when you start using it from your own C++ code.

The bottom line is that the exception is not coming out of nowhere.

Tom

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