Re: Help please: Trouble getting a value back from COM.

Darrin,
I'm not sure this is a problem with jawin yet.

You Garbage method needs some tweaks for it to work with plain C++.
[out] parameters must be passed by reference or pointers. Since COM does not
deal with C++ references we'll use a pointer type:

STDMETHODIMP CValidateLogin::Garbage(
    /*[in]*/ BSTR InputString,
    /*[in]*/ int InputInt,
    /*[out]*/ BSTR *returnString)
{
 *returnString = CString(_T("blah")).AllocSysString();
 return 0;
}

Robert
-----Original Message-----
From: Discussion of Java/Win32/COM integration with Jawin
[mailto:[email protected]] On Behalf Of Darrin Smith
Sent: Friday, June 04, 2004 9:10 AM
To: [email protected]
Subject: [JAWIN] Help please: Trouble getting a value back from COM.

How do you need to set up the COM side to be able to get a value back to
your Jawin application without using simple getXXX methods? In other words,
I'd like to have a method that returns a value based on a parameter I send.

For example, I have a DLL that had a method that looks like this:

STDMETHODIMP CValidateLogin::Garbage(BSTR InputString, int InputInt, BSTR
returnString)
{
 returnString = CString(_T("blah")).AllocSysString();
 return 0;
}

I can call this just fine, but of course I can't get the value back out
(call by value on the returnString), so I modified the Garbage method to
take an array. It ended up looking like this:

STDMETHODIMP CValidateLogin::Garbage(BSTR InputString, int InputInt,BSTR
returnString[1])
{
 returnString[0] = CString(_T("blah")).AllocSysString();
 return 0;
}

This compiled just fine after changing the IDL and header file, but when I
ran it through the Jawin Type Browser, it would hang (out of memory I
think...even after I upped it to 256meg).

Next, I and a coworker (COM guy) tried to use a VARIANT like this:

STDMETHODIMP CValidateLogin::Garbage(BSTR InputString, int
InputInt,VARIANT* returnString)
{
 returnString->bstrVal = CString(_T("blah")).AllocSysString();
 return 0;
}

When that is run through the Jawin Type Browser, it ends up with this:

public void Garbage(String InputString,int InputInt,Variant[] returnString)
throws COMException
{
   invokeN("Garbage", new Object[] {InputString, new Integer(InputInt),
returnString});
}

This is just fine, but when I run this:

Variant[] v = new Variant[5];

      iLogin.Garbage("InputString", 5, v);

it gives me this error:

An unexpected exception has been detected in native code outside the VM.
Unexpected Signal : EXCEPTION_ACCESS_VIOLATION (0xc0000005) occurred at
PC=0x7715CB4D
Function=SafeArrayAllocDescriptor+0xA0
Library=C:\WINDOWS\system32\OLEAUT32.dll
Current Java thread:
 at org.jawin.marshal.GenericStub.dispatchInvoke0(Native Method)
 at org.jawin.marshal.GenericStub.dispatchInvoke(GenericStub.java:84)
 at org.jawin.DispatchPtr.invokeN(DispatchPtr.java:473)
 at org.jawin.DispatchPtr.invokeN(DispatchPtr.java:433)
...


So, my question is, how are you supposed to get a value back from COM?

Can someone provide me with an example please? This should be simple to do
but I can't find any example of how to do it using Jawin.

THANKS!