Using ActiveX created in VB

[SkidMark75]

I have an ActiveX control created in Visual Basic that I'm trying to use in my Visual C++ app. I'm having a little trouble with one of the functions of the control.

The definition of the function looks like this:

Public Function GetStrVal(ByRef strVal As String) As Long

I have an instance of this control and I'm trying to call this function but I'm getting a compiler error. Here is how I'm using it:

CString str;
long lIndex = m_obj.GetStrVal(str);

which results in the following compiler error:

cannot convert parameter 1 from 'class CString' to 'unsigned short ** '

I found a way around it but I don't like it much:

_bstr_t bstrTemp;
BSTR Temp = bstrTemp;
long lIndex = m_obj.GetStrVal(&Temp);

Can anyone tell me the "correct" way or at least a "better" way of doing this? I can change either the VB side or the C++ side.

[kirants]

This is good enough..

BSTR Temp;
long lIndex = m_obj.GetStrVal(&Temp);
//use the Temp
//when done, free it
SysFreeString(Temp);

[Vi2]

This is good enough..

No, it's not. The variable should be initialized because the VB's ByRef parameter is [in,out] one.

BSTR Temp = NULL; // or SysAllocString(...)

[kirants]

No, it's not. The variable should be initialized because the VB's ByRef parameter is [in,out] one.

BSTR Temp = NULL; // or SysAllocString(...)

Thanks for correcting.. Don't know about VB
Anyways, in that case, how would Temp = NULL work ? I would assume VB would expect a valid BSTR if it is an in param , right ?

[Vi2]

Anyways, in that case, how would Temp = NULL work ? I would assume VB would expect a valid BSTR if it is an in param , right ?

The C's NULL is the valid BSTR value and equals the VB's vbNullString. There is an equivalence for "" and vbNullString: both are the empty strings.

[kirants]

OK. Just wanted to know. Because if it is a [in,out] , then VB would have to either SysFree/SysRealloc the in param. I beleive VB would handle this case.

Thanks for the info, BTW