Hi

I have a C# DLL which has a method which accepts a string argument. This is
registered for COM. The resulting .tlb is then referenced in a native C++
DLL. I then wrap the method in a C++ method and add some trace code. The
wrapped C# method also includes some trace code. When I attempt to run the
C++ method, passing a BSTR to it, the C++ methods trace code fires, however,
the C# method call doesn't appear to do anything.

The strange thing is that if I remove the string argument from the C#
method, regenerate the .tlb and change the wrapper method accordingly the C#
trace code fires. I have other methods which accept and return numeric
types which issue, it's just this one which accepts a BSTR that seems to be
a problem.

I should say that the C++ dll has to be native to integrate with an ancient
PowerBuilder component which can't be changed, hence the C++ to COM to C#
process.

I'm rather lost on this one, as I know almost nothing about C++, so I'd
really appreciate if anyone can give me a few pointers (no pun intended).

Many Thanks

Glenn

GlennAnthonyB wrote:
executed or does it hang?


--Johannes


--
Johannes Passing - http://int3.de/

"Johannes Passing" <jpassing_at_hotmail_com (AT) nospam (DOT) com> wrote

It's doesn't hang, it just doesn't appear to enter the C# method.

C# code fragment...

public int Search( string searchString )
{
Trace.TraceInformation( "Managed Search method invoked..." );

int status = -1;

return status;
}

C++ code fragment...

#include "stdafx.h"

#import "Test.tlb" raw_interfaces_only

BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
CoInitialize( NULL );
return TRUE;
}

int Search( BSTR searchString )
{
long lResult = 0;

Test::ISearchEnginePtr searchEngine( __uuidof( Test::SearchEngine ) );

searchEngine->Search( searchString, &lResult );

printf( "result %d", lResult );

return lResult;
}


Thanks

Glenn

Interesting point is that if I create a BSTR in the C++ method I can pass
that to the COM wrapped C# method and it works. The issue is using the BSTR
argument passed to the C++ method.


"glennanthonyb" <glenn.csharp (AT) yahoo (DOT) co.uk> wrote

Hi Glenn,

first, there are some issues with your DllMain. DllMain is not only
called on initialization but also on termination of process/threads, so
you definitely need to switch on ul_reason_for_call rather than always
perform the same action. Furthermore, you should never call CoInitialize
from DllMain - see [1] for details. Depending on the calling
application, this might even be the reason for your problem, so try to
fix this first.

To use COM in a DLL, create a helper thread (in the C++ Search function)
and perform all COM-related work on this thread.

[1] http://download.microsoft.com/download/a/f/7/
af7777e5-7dcd-4800-8a0a-b18336565f5b/DLL_bestprac.doc

--Johannes


--
Johannes Passing - http://int3.de/

Thanks for the info, appreciate it.

Glenn

"Johannes Passing" <jpassing_at_hotmail_com (AT) nospam (DOT) com> wrote