Re: VARIANT as [out] parameters - COM Discussion Boards

Problem in passing recordset from server to client

ramjan24-Jan-02 3:05

24-Jan-02 3:05

Hello,

I have some sort of problem in COM while passing the ADO recordset

object through variant to the client. In the server I can able to traverse

through the recordset Blush | :O

. Once I got the variant at the client end, the variant

contains the NULL (VT_EMPTY) Confused | :confused:

.

What is the problem? For your clarity I'm putting some excerption from my

coding.

At Server_End

HRESULT CServer::Function1(VARIANT *pvarRSObj, VARIANT *pvarRetVal)
{
_RecordsetPtr pRSObj = NULL;

try
{
pRSObj->CreateInstance(__uuidof(Recordset));
pRSObj->Open(varQueryString, (IDispatch*)m_conObj,

adOpenKeyset, adLockBatchOptimistic, adCmdText);

pvarRSObj->vt = VT_DISPATCH;
pvarRSObj->pdispVal = (IDispatch*)pRSObj;
}
catch(_com_error &e)
{
ERRBOX(e.ErrorMessage());
return e.Error();
}
catch(...)
{
ERRBOX("Unknown Exception");
return E_FAIL;
}
return S_OK;
}

At Client_End

InvokeServer()
{
IServer *pServer;
//instantiation of server

pServer->Function1(&varRSObj, &varResponse);

CHECKVARIANTTYPE(&varRSObj); //It'll check the variant type
// this is showing me that variant contains VT_EMPTY.
if(varRSObj.vt == VT_DISPATCH)
{
//necessary action
}
}

Timely reply appreciated.

Regards,
Ramesh

Re: Problem in passing recordset from server to client

Shadi Al-Kahwaji24-Jan-02 3:33

Shadi Al-Kahwaji

24-Jan-02 3:33

Hi,

You can return a Recordset as an IDispatch pointer like this:

STDMETHODIMP CMyClass::GetAllRecords(BSTR bstrSearchKey, IDispatch **output)
{
....
....

*output = (IDispatch*) pRecordset.Detach(); //Return recordset as IDispatch
}

Regards,
ShadiK

Shadi Al-Kahwaji

ExecWB method on IE 5.0 ! (Urgent)

rieta22-Jan-02 21:21

rieta

22-Jan-02 21:21

I am hosting IWebBrowser2 in my application. The problem is that "cut & copy" of the default context menu were not working. Whenever I tried to copy ,"Acces is denied" alert box comes up. So I implemented my own context menu using "ShowContextMenu" of IDocHostUIHandlerDispatch interface. I used IOleCommandTarget for delete, and implemented copy and cut on my own. However, my code does not work on IE 5.0. What should I do?. Are the IOleCommandTarget's Exec method or IWebBrowser's ExecWB method not availabe on 1E 5.0 .
These functions do not work on Win98 also. Is there any other way of doing these in win98?Please help. I am in urgent need.

Re: ExecWB method on IE 5.0 ! (Urgent)

28-May-02 2:16

uyiyuiyuncvnvbmnvbmnvbmsdgsdgfsdf!!!!!!!!!!!!

-858993460

22-Jan-02 8:30

when i try to return an integer Locally, everything goe's smooth.
but when i try it remotely i get the next number:-858993460
whatever the input is.

Plese Help!

Re: -858993460

Jamie Hale22-Jan-02 10:58

Jamie Hale

22-Jan-02 10:58

Ok, did you look at the conversion? -858993460 is 0xCCCCCCCC which is usually what you find in uninitialized memory when running in debug mode.

Are you initializing the variable that you're returning? Just a guess.

J

VARIANT as [out] parameters

Nick Blumhardt21-Jan-02 16:34

Nick Blumhardt

21-Jan-02 16:34

Hi all,

When outputting a VARIANT from a COM interface member (as an [out] parameter, not [in, out]), should I call ::VariantClear() or ::VariantInit() on the output parameter before assigning to it? Or is this redundant/incorrect?

e.g.:

STDMETHODIMP MyFunc (/*[out]*/ VARIANT* pVal)
{
VariantInit (pVal); // ok?
pVal->vt = ....
...
}

cheers

NB

Re: VARIANT as [out] parameters

Rashid Thadha22-Jan-02 11:34

Rashid Thadha

22-Jan-02 11:34

See sample app of COM Variant and Safearrays at

http://www.sellsbrothers.com/tools/CComSafeArray.zip

(from chris sells site)

Remote on win95

newbe21-Jan-02 9:10

newbe

21-Jan-02 9:10

Helllo everybody:
I have a DCOM server that returns an integer. This server runs on a win95 machine. When i connect everything goes fine but when i try to return the integer from the server, The client stops immidiatly. Is there enyone who ever had the same problem.
I preciate your Help..

Re: Remote on win95

Henrik Sternberg24-Jan-02 1:45

Henrik Sternberg

24-Jan-02 1:45

Not knowing exactly what you are doing, it sounds as if the integer datatype is different between the client and the DCOM server. What kind of client are you using?

I have had this problem and I solved it by using the BSTR datatype. To do "pure COM" and being on the safe side, you should always pass BSTR:s as parameters, since they will be the same on both client and server side. This leads to a bit more of converting, but that's life Wink | ;)

Best regards,

/_henrik

Henrik Sternberg,
Cambridge Technolgy Partners, Germany
www.ctp.com/ce

henrik.sternberg@ctp.nospam.com
(take away nospam)

Does the number of events affect Performance ??

Firoz17-Jan-02 19:00

Firoz

17-Jan-02 19:00

Hi,

I have a DCOM application, where the component fires 8-10 events.
But all the events are similar in structure. (ie. they doesnt have any data associated with them).
The only difference is the event name.

So, I can easily use a single event to Notify all my events to
the client (And have some Parameter that distinguishes the event
to the client).

Now, my question is will this (using a single event in place of many events)
provide any PERFORMANCE benefits in a DCOM application ??

if yes, How ?? (some technical description will be appreciated)

anyway, the number of Network RoundTrips is going to be the same...

if no,
What will be a good COM programming practice in this situation.
(using a Single event or using different events)

Please somebody reply ... Frown | :(

I had posted this earlier, but got no response...

Thanks,

Firoz.

Re: Does the number of events affect Performance ??

Not Active18-Jan-02 2:42

Not Active

18-Jan-02 2:42

From a mantainability and debugging point of view combining all events into a single one would of course be more beneficial.

I don't believe I've seen any performance difference in using multiple events rather than a single one, as you said the round trips will be the same.

Re: Does the number of events affect Performance ??

Jamie Hale22-Jan-02 8:54

Jamie Hale

22-Jan-02 8:54

Firoz wrote:
the number of Network RoundTrips is going to be the same...

How do you figure? As I see it, DCOM needs to setup for each call. If you only call once, this setup (marshalling and whatnot) is only done once. If you do many calls, this setup needs to be done each time. Sure the amount of data (from your point of view) being sent is the same (1 x 10 events or 10 x 1 events), but I think you need to take into consideration the setup and teardown of the connection.

Please correct me if I'm wrong. Smile | :)

BSTR

newbe17-Jan-02 2:10

newbe

17-Jan-02 2:10

Hello, can somebody please help me:
i'm trying to write a string to a file serverside. and i want to get the string back. So i use the next function:
MIDL :write [in]BSTR message
cpp: HRESULT Write(BSTR message)
{
//code to write to a file on the server
}
can u please explane how the BSTR type works and how can i convert it to a normal string

Re: BSTR

Carlos Antollini17-Jan-02 2:38

Carlos Antollini

17-Jan-02 2:38

CString str = _T("")
str = message;

Carlos Antollini.
Sonork ID 100.10529 cantollini

Re: BSTR

Not Active17-Jan-02 5:28

Not Active

17-Jan-02 5:28

CString str(message)

Re: BSTR

Ernest Laurentin17-Jan-02 5:26

Ernest Laurentin

17-Jan-02 5:26

One of the easiest way to use the BSTR type as normal string, in my opinion is
to use the compiler string type: _bstr_t
Use like this:

HRESULT Write(BSTR message)
{
 _tprintf(TEXT("Message:%s\r\n", (LPCTSTR) _bstr_t(message));
}

You can look at the description for _bstr_t in MDSN for more help.
It can also convert ASCII string to Unicode. You may want to use conversion macro.

HRESULT Write(BSTR message)
{
USES_CONVERSION;
LPCTSTR lpszNormal = OLE2CT(message);
 _tprintf(TEXT("Message:%s\r\n", (LPCTSTR) lpszNormal);
}

Re: BSTR

Not Active17-Jan-02 5:29

Not Active

17-Jan-02 5:29

CComBSTR

Re: BSTR

pba_24-Jan-02 7:17

pba_

24-Jan-02 7:17

MultiByteToWideChar / WideCharToMultiByte or mbstowcs / wcstombs Wink | ;)

Re: BSTR

yamini13-Feb-02 1:14

yamini

13-Feb-02 1:14

There are 2ways to do this
The first method uses the OLE2T() for BSTR conversion to string.

The second method uses _bstr_t for conversion.
******************************************************#inclu#include <iostream.h>
#include <atlbase.h>
#include <comdef.h>
void main()
{
BSTR b=L"StringConversion"; //BSTR string
USES_CONVERSION; //First method of Conversion
cout<<"String :"<

Events in MFC client

Member 1697717-Jan-02 1:26

Member 16977

17-Jan-02 1:26

Hi,All
I have a component(built using ATL) which supports outgoing interfaces.I want to use this component in MFC client.
When component fires an event i want to trap it and show the string which it sends in the modeless dialog box.
I dont know how to trap events in MFC client.
Can anybody help.
Regards
Tushar

Re: Events in MFC client

Prem Kumar19-Jan-02 10:58

Prem Kumar

19-Jan-02 10:58

Look at the MSDN KB article Q181845.
"HOWTO: Create a Sink Interface in MFC-Based COM Client".

regards,
Prem

Re: Events in MFC client

Matt Philmon13-Feb-02 17:51

Matt Philmon

13-Feb-02 17:51

Let me know if you get really stuck. Connection Points are just as unbelieably hard to handle in MFC applications as they are easy in VB. I can give you some details or examples if you need it.

Deleting mutiple instances of COM object

Ebin16-Jan-02 20:01

Ebin

16-Jan-02 20:01

We have implemented a com client in VC++ and it should communicate with server that developed in Delphi(.dll).

The Scenario is as folows
-------------------------------------

A button click on com client(vc) will invoke the com server (Delphi interface)(dialog based).
which will display a dialog were user can interact.Thus by the button click on VC client(dialog based) can invok multiple instances of delphi server.

Now we need to delete or close all the instances of com server with a single click in vc client (com client)
how it is possible ?.

Thanks in Advance
eby

Re: Deleting mutiple instances of COM object

Henrik Sternberg18-Jan-02 1:02

Henrik Sternberg

18-Jan-02 1:02

Hello Eby,

What kind of server is it? (IN/OUT of process)

Can you provide more details?

Regards,

/_henrik

Henrik Sternberg, Consultant
Cambridge Technolgy Partners, Germany
www.ctp.com/ce

henrik.sternberg@ctp.nospam.com
(take away nospam)

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.