I'm having trouble making changes to parameters passed to
my COM object and then having the changes appear in the
calling VBScript.

DESIRE:
I would like to pass a variable from VBScript to my ATL
COM object and have the ATL COM object modify the value.

PROBLEM:
My ATL COM object is getting called from VBS as expected,
but if I change the parameters value, the value us
unchanged when we return to VBScript.

Here is the VBScript:

Function test(xx)
  ' my COM object
  Set UOTCtrl = CreateObject("UOTCtrl.Application")
  ' the session handle I want to fill in
  ' (We set it to 12 just so we can check it in the called
routine)
  hSession = 12
  ' This will call my COM object to fill in the session
handle
  ' I check it in my COM routine and it is indeed(12)
  UOTCtrl.Connect(hSession)
  ' At this point however, the session is still 12!!
  UOTCtrl.Disconnect(hSession)
End Function

Here is my Method Implementation:

STDMETHODIMP CApplication::Connect(unsigned long* hSession)
{
        HANDLE res = (HANDLE)13;
        *hSession = (unsigned long)res;
        return S_OK;

STDMETHODIMP CApplication::Disconnect(unsigned long
hSession)
{
        bool res = (hSession == 13);
        return res ? S_OK : S_FALSE;

Here is my IDL:
[id(13), helpstring("method Connect")] HRESULT Connect
(unsigned long* hSession);
[id(14), helpstring("method Disconnect")] HRESULT
Disconnect(unsigned long hSession);

And my Class interface:
// IApplication
public:
STDMETHOD(Disconnect)(unsigned long hSession);
STDMETHOD(Connect)(unsigned long* hSession);

So, what have I done wrong? Connect takes a unsigned
long*, so my code that assigns to it:
*hSession = (unsigned long)res;
Should change it, eh?

Q197957 - PRB: Passing Parameters By Reference to a VC COM Object
http://support.microsoft.com/default.aspx?kbid=197957

--
Michael Harris
Microsoft.MVP.Scripting
Seattle WA US

Well the article you pointed me to seems to be addressing
my problem, but it still doesn't work :(

Here is the error I get now:
Error: Wrong number of arguments or invalid property
assignment: 'UOTCtrl.Connect', ; in line 5

I tried changing the IDL from [out,retval] to [out] and
that seemed to eliminate the error message, but then we're
back to having the change made in 'Connect' not make it
back up to to VBScript.

Here's my VBScript function:

Function test(xx)
 Set UOTCtrl = CreateObject("UOTCtrl.Application")
 hSession=123
 UOTCtrl.Connect(hSession)
 test = hSession
End Function

The problem is that the function always returns 123, even
when I change the VARIANT as described in the article.

Any further help would be greatly appriciated.

For the record, here are the changes I made per the
article:

STDMETHODIMP CApplication::Connect(/*[out, retval]
*/VARIANT* vVal)
{
 HANDLE res = (HANDLE)Start();
 vVal->vt = VT_UINT;
 vVal->uintVal = (UINT)res;
 return res ? S_OK : S_FALSE;

// IDL
[id(13), helpstring("method Connect")] HRESULT Connect
([out/*, retval*/] VARIANT* vVal);

Sorry...

If I actually knew anything about coding in VC++/ATL (other than how to
spell it ;-), I could probably help more.

But I don't, so I can't :-(

--
Michael Harris
Microsoft.MVP.Scripting
Seattle WA US

That makes sense since the COM method modifies the passed argument rather
than returning a value.  You should be aware that while VBScript supports
pass by reference, JScript does not, so you exclude any JScript clients.

This should be:

   UOTCtrl.Connect hSession 'preferred syntax

or

  Call UOTCtrl.Connect(hSession) 'OK but unnecessary

When calling a COM method that does not return a value (in VBScript
terminology, a Sub as opposed to a Function that does return a value), ()s
are not used to enclose the argument list unless you explicitly use the Call
statement.

In the case of calling a method that takes only a single argument, using the
otherwise unnecessary ()s around the single argument turns the argument into
an expression, the value of which is passed to the method.  The method
expects a byref argument but ends up modifying the temporary memory holding
the value of the expression rather than the memory representing the client
variable within the expression.

If your COM method had expected 2 arguments, then

  UOTCtrl.Connect(hSession, arg2)

would have thrown a runtime error of "cannot use parentheses when calling a
Sub" and the problem would have been more obvious...

--
Michael Harris
Microsoft.MVP.Scripting
Seattle WA US

passed argument rather
JScript clients.

I'm adding VBScript to my application (not web page) via
the Scripting Control (VBX?) so there is no concern of
JScript.

So the question remains...
How do I pass a parameter to a COM control and have the
modified parameter passed back up to the calling script?
This *must* be possible!

return a value), ()s
explicitly use the Call
turns the argument into
temporary memory holding
representing the client
parentheses when calling a

I think you didn't read all of my reply which was inline in 2 parts ;-)...

--
Michael Harris
Microsoft.MVP.Scripting

Hey Michael thanks! That worked like a charm.
(I also *understand* what was happening.)

I'm a bit surprised that using parentheses for function
arguments would change the program semantics so radically.
Oh well.
Heh, I've been programming in C (and the like) for 20
years... not putting parentheses after a function call is
a hard habit to break ;P

Anyway, thanks again.
Luke