NULL returned from COM dll crashes VB app.

[TheMillionDollarMan]

Hi,

We have an application written in C++. We have exposed some of the objects in a COM dll.

Now when the VB application calls one of the methods in the COM dll that returns a NULL the VB application blows up.

Normally when using the same method in C++ we can handle the NULL return type no problem.

How can we handle the null return type?
1. Change all of the methods in the C++ object so that they never return a null.

2. set one of the project configurations? NMAKE?

3. Avoid the VB application calling the NULL returning methods. Not feasible as its a distributed software component.

I would like some suggestions as there are 1000's of methods and I don't want to have to code the

return MethodMayReturnNull() = NULL : 0 : MethodMayReturnNull();

Thanks..

 

[palbano]

>> Now when the VB application calls one of the methods in
>> the COM dll that returns a NULL the VB application
>> blows up.

I don't understand. VB uses IDispatch

HRESULT Invoke(
DISPID dispIdMember,
REFIID riid,
LCID lcid,
WORD wFlags,
DISPPARAMS FAR* pDispParams,
VARIANT FAR* pVarResult,
EXCEPINFO FAR* pExcepInfo,
unsigned int FAR* puArgErr
);

So your code returns NULL for the HRESULT? It's not supposed to do that.

-pete

 

[TheMillionDollarMan]

Whoops.

Sorry you're right. My problem is that the C++ object is returning NULL and causing the problem.

Thanks for you're help anyway.