Re: Raise Errors from non-coclasses

"Igor Tandetnik" <>
Tue, 4 May 2010 11:42:34 -0400
Barzo <> wrote:

On 4 Mag, 16:43, "Igor Tandetnik" <> wrote:

Hmm. The way AtlReportError (or, to be precise, AtlSetErrorInfo) is
written, it never sets the description to NULL. If you try to pass
NULL to it (as you did), it generates a default string "Unknown
Error" (as you observed).
I suppose you'll have to write your own helper function similar to
AtlSetErrorInfo. You can look at its implementation in atlcom.h

I follow the "instruction" of the MS link, by the way:
"The Visual Basic runtime uses the ISupportErrorInfo interface to
determine whether an object supports the rich error mechanism. If the
object supports the rich error mechanism, a call is made to the
GetErrorInfo method to retrieve the available error information. The
runtime then determines whether bstrDescription has a value other than
NULL. If the runtime finds a value other than NULL, Visual Basic
cannot translate the HRESULT value to an error number that complies
with Visual Basic. By default, the raw HRESULT value is used in this
"..If the runtime finds a NULL value, HRESULT retrieves an error
number and a description that apply to Visual Basic. Visual Basic then
uses HRESULT to look up the corresponding Visual Basic error. If a
match exists, Visual Basic uses the error number and the description
that comply with Visual Basic."
I understood that VB retrieve the description from the HRESULT I don't know! :-(

I'm not sure I understand the source of your confusion. VB only does =
this special translation when the error comes with the description of =
NULL, otherwise it uses HRESULT as is. Unfortunately, ATL's helper =
function AtlReportError never sets the description to NULL. So, you =
can't use this helper function for your purposes. Now, this helper =
function is just a thin wrapper around underlying API; in fact, its =
source code is easily available so you can see exactly how it calls said =
API. Thus, you can just call that API directly, to set up the error the =
way you need it.
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not =
necessarily a good idea. It is hard to be sure where they are going to =
land, and it could be dangerous sitting under them as they fly overhead. =
-- RFC 1925

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