_bstr_t class is using reference counted BSTR inside this class.
What is happening here is that when you return _bstr_t from
ExtractAddErrInfo, C++ is creating temporary instance, which
will live only during assignment operation to _bstr_t val and
it will be destroyed right after assignment operation.
It means, that val now has a pointer to already destroyed
BSTR, hence crash when it is trying to destroy it again
in the destructor.
I am not judging your design of ExtractAddErrInfo function, so
the easiest way to fix it is:

_bstr_T val = CErrorUtil::ExtractAddErrInfo(bstrIn).Copy();

This is not a bug in _bstr_t, just improper use of it.

Regards,

Alex Shevchuk

> -----Original Message-----
> From: S.Pradhan [mailto:sabyasachi.pradhanKLA-TENCOR.COM]
> Sent: Wednesday, March 20, 2002 8:26 PM
> To: DCOMDISCUSS.MICROSOFT.COM
> Subject: bug in _bstr_t ????
>
>
> I have the following problem.
>
> I have a win32 Dll(non COM ordinary Dll).The dlll exposes a
> method which
> takes in a _bstr_t as a parameter and returns a _bstr_t
> parameter.Inside the
> method i do some manipulation with the passed in bstr and
> return it.When i
> call it from another application(say a console app), the
> function returns
> succesfully, but at the caller app when the returned bstr
> goes out of scope
> it crashes.
> Why does it happen so.If i replace _bstr_t with CComBSTR or
> _variant_t data
> type, everything works fine without any problem.
> Look like there is a bug in _bstr_t.
>
> I know all of you might say, that i am not handling the
> memory properly when
> i manipulate the bstr in the method and return.Hence i am
> giving the code
> here.
>
> Pl et me know if i am doing anything wrong here fundamentally
> or there is a
> problem with _bstr_t.
>
> The error.h file of the win 32 DLL
>
> **************************************************************
> ************
> #ifdef ERROR_API_EXPORT
> #define ERROR_API __declspec(dllexport)
> #else
> #define ERROR_API __declspec(dllimport)
> #endif
>
> #include<comdef.h>
> //#include<atlbase.h>
> class ERROR_API CErrorUtil
> {
>
> public:
> static _bstr_t ExtractAddErrInfo(_bstr_t bstrErrMessage);
> private:
> // This class is not meant to be instantiated; therefore,
> the constructor
> is
> // made a private member.
> CErrorUtil(void);
> };
>
> **************************************************************
> ***********
>
> The error.cpp of the win 32 DLL
>
> **************************************************************
> *************
> #include "error.h"
>
> _bstr_t CErrorUtil::ExtractAddErrInfo(_bstr_t bstrErrMessage)
> {
>
> _bstr_t batrval2("Pradhan");
> bstrErrMessage=batrval2;
>
> return bstrErrMessage;
>
> /*tried with Following line, still it crashes */
> //return bstrErrMessage.copy() ;
> //return ::SysAllocString((OLECHAR*)bstrErrMessage);
>
> }
>
> **************************************************************
> *************
>
>
> Console client.cpp
> **************************************************************
> *************
> #include<comdef.h>
>
> #include "D:\Scratch Area 2\testproject\Error\error.h"
> #include<stdio.h>
> void main()
> {
> CoInitialize(NULL);
> try
> {
> _bstr_t bstrIn="Rajesh";
> _bstr_t val=CErrorUtil::ExtractAddErrInfo(bstrIn);
>
> }///it crashes here, when the _bstr_t val gets destroyed.
> catch(_com_error &e)
> {
>
> }
> CoUninitialize();
> }
> **************************************************************
> *************
>
> ----------------------------------------------------------------
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