Re: dual interface for IDispatch - C / C++ / MFC Discussion Boards

CPallini15-Feb-08 3:10

15-Feb-08 3:10

George_George wrote:
If I remember correctly (I am not VB expert), in VB to access some object in COM, we have to program in the way above, does it mean VB always use later binding?

2.

Do you mean there are any other ways to access VB in COM, that is not later binding?

No. You can also, for instance, import into your VB6 project the MSComm object as ActiveX control at design time, say MSComm1 and then use it inside code, this way you will use early binding and VTABLE access to the component.

George_George wrote:
3.

Later binding means runtime binding, right? In runtime, using invoke method on the IDispatch interface of the component?

Yes.

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

Re: dual interface for IDispatch

George_George15-Feb-08 3:41

George_George

15-Feb-08 3:41

Thanks CPallini,

1.

For the later binding case (suppose client will use invoke, other than vtabke), I am wondering during compile/build phase, how will the client (C++, VB, VBScript, etc.) utilize the TLB file? Does the contained interface function information be read and checked?

(I think the answer is no)

2.

So, all the interface/function/parameter checking work in done during runtime?

regards,
George

Re: dual interface for IDispatch

CPallini15-Feb-08 4:01

CPallini

15-Feb-08 4:01

George_George wrote:
1.

For the later binding case (suppose client will use invoke, other than vtabke), I am wondering during compile/build phase, how will the client (C++, VB, VBScript, etc.) utilize the TLB file? Does the contained interface function information be read and checked?

(I think the answer is no)

Type libraries are not used in late binding case.

George_George wrote:
So, all the interface/function/parameter checking work in done during runtime?

Yes this the automation mechanism.
Automation client need only IDispatch interface, all of the server functionality is accessed via IDispatch methods (i.e. GetIDsOfNames, Invoke, ..)

Smile | :)

Re: dual interface for IDispatch

George_George16-Feb-08 22:33

George_George

16-Feb-08 22:33

Thanks CPallini,

Quite interesting, you mean if we write statement like this in VB (later binding),

Dim objSer as Objectset
objSer = CreateObject("MSCOMMLib.MSComm")

during compile/build phase in VB, nothing is checked? Even if the component progID MSCOMMLib.MSComm is not checked?

(if yes, type library is not used at compile/build time)

regards,
George

Re: dual interface for IDispatch

CPallini16-Feb-08 23:04

CPallini

16-Feb-08 23:04

Exactly, the following code succesfully compiles on my system

Private Sub Command1_Click()
    Dim obj As Object
    Set obj = CreateObject("George.George")
End Sub

Re: dual interface for IDispatch

George_George16-Feb-08 23:32

George_George

16-Feb-08 23:32

Thanks CPallini,

My question is answered! You are so knowledgeable! Cool!!

regards,
George

Re: dual interface for IDispatch

Rajkumar R15-Feb-08 0:14

Rajkumar R

15-Feb-08 0:14

George_George wrote:
once we inherit from IDispatch interface, then it is always a dual interface, right?

why u said so.

George_George wrote:
What type of implementation in C++ for a component is not a dual interface? I can not imagine a sample

I think ur confusion is once derived from IDispatch in C++, u have access through vtbl (atleast of IDispatch) and also through Invoke(), dual implicit and why u need dual keyword. Is it?

Re: dual interface for IDispatch

George_George15-Feb-08 0:28

George_George

15-Feb-08 0:28

Yes Rajkumar,

Rajkumar R wrote:
I think ur confusion is once derived from IDispatch in C++, u have access through vtbl (atleast of IDispatch) and also through Invoke(), dual implicit and why u need dual keyword. Is it?

Sometimes I notice that the component actually implements the dual interface, but in the IDL file, "dual" property is not added to the interface property.

1. Is it good practice?

2. What is the purpose of doing so? Force user to use IDispatch other than efficient vtable?

3. Could we use vtable even if dual property is not added to interface? For example, using QueryInterface to get come component interface (other than IDispatch and IUnknown)? If we could, then it is a dual interface activity -- invoking through vtable.

regards,
George

Re: dual interface for IDispatch

Rajkumar R15-Feb-08 4:43

Rajkumar R

15-Feb-08 4:43

yes!! I guessed correctly, u misunderstood the concept of dual interface in OA.

direct vtable-based interfaces as u expect are called "custom interfaces" and invocation through IDispatch are called "automation" or "dispatch interfaces" the "custom interfaces" may need to be accessed after a query interface and may needs custom marshalling. Dual iterfaces can be accessed without a query interface and gets standard marshalling support like dispatch interfaces.

a comparison of these 3 interfaces is here [^]

Re: dual interface for IDispatch

George_George16-Feb-08 22:36

George_George

16-Feb-08 22:36

Thanks Rajkumar,

Sorry that I may not made myself understood. My question is, if I do not declare the interface as dual in IDL file, but actually in implementation, I implemented the dual approach.

Could the client of the component (e.g. in case of C++ client) utilize vtable other than through IDispatch?

regards,
George

Re: dual interface for IDispatch

Rajkumar R17-Feb-08 0:09

Rajkumar R

17-Feb-08 0:09

George_George wrote:
but actually in implementation, I implemented the dual approach.

again, don't confuse it with "custom interface"

George_George wrote:
Could the client of the component (e.g. in case of C++ client) utilize vtable other than through IDispatch?

yes, u can, use queryinterface and get ur "custom interface".

Re: dual interface for IDispatch

George_George17-Feb-08 0:23

George_George

17-Feb-08 0:23

Thanks Rajkumar,

Seems the dual property does not enforce compile/link/runtime's strong checking about whether or not the component implements dual interfaces (if the component does not implement dual interface, and there will not be any compile/link/runtime error if component only implemeents IDispatch)? Right?

And similar to the situation when we do not add dual, compile/link/runtime does not enforce strong checking and gives warning or error message when client tries to use dual interface (both vtable and IDispatch), right?

regards,
George

File Comparison in VC++6.0

seshi_hari14-Feb-08 21:36

seshi_hari

14-Feb-08 21:36

Hi,
I need to compare two text files in VC++6.0, whose contents have been displayed in two richedit controls.Also i need to highlight the differences that exists in the two files......Can any one help me out?

Re: File Comparison in VC++6.0

Cedric Moonen14-Feb-08 21:41

Cedric Moonen

14-Feb-08 21:41

See point 2 here[^]

Cédric Moonen
Software developer

Charting control [v1.2]

Re: File Comparison in VC++6.0

Rajesh R Subramanian14-Feb-08 21:43

Rajesh R Subramanian

14-Feb-08 21:43

What have you tried so far? Where are you stuck?

Re: File Comparison in VC++6.0

seshi_hari14-Feb-08 23:29

seshi_hari

14-Feb-08 23:29

i have displayed the contents of the files in the richeditcontrols.I dont know how to compare the files and highlight the differences in them.The codes which i got by surfing the net just tell whether the files are equal or not.They just return an int or bool value.Here is the place i got struck.

Re: File Comparison in VC++6.0

Rajesh R Subramanian15-Feb-08 0:12

Rajesh R Subramanian

15-Feb-08 0:12

I think it's rather a complex task. I don't think you will get the "code" here right away. You may have to look at the XDiff[^] project. Perhaps that would help you.

Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP

Re: File Comparison in VC++6.0

Nemanja Trifunovic15-Feb-08 3:54

Nemanja Trifunovic

15-Feb-08 3:54

My condolences. I had to do the exactly same thing some 5 years ago, and ended up with a post "I hate MFC" in the Lounge Smile | :)

Anyway, to find the differences between files, use Longest Common Subseqence Algorithm[^] - that would be the easy part.

Now, for displaying it in the richedit controls - good luck with that Smile | :)

Programming Blog

utf8-cpp

checking for instance validity

rp_suman14-Feb-08 21:26

rp_suman

14-Feb-08 21:26

How to check the instance of the class is valid or it is not especially in multi threaded program?

Best Regards,
Suman

Re: checking for instance validity

Cedric Moonen14-Feb-08 21:29

Cedric Moonen

14-Feb-08 21:29

rp_suman wrote:
How to check the instance of the class is valid

What do you mean exactly ? Can you be more explicit please. What does 'valid' mean ?

Cédric Moonen
Software developer

Charting control [v1.2]

Re: checking for instance validity

Prasanth M V14-Feb-08 23:08

Prasanth M V

14-Feb-08 23:08

Suman,

Plz give more deatils....what is actually men by 'valid'.
It will be better if u provide with some code fragment that u are using.....

Prasanth Smile | :)

Re: checking for instance validity

Prasanth M V14-Feb-08 23:13

Prasanth M V

14-Feb-08 23:13

HI,

Plz give more deatils....what is actually mean by 'valid'.
It will be better if u provide with some code fragment that u are using.....

prasanth Smile | :)

Re: checking for instance validity

Maxwell Chen14-Feb-08 23:19

Maxwell Chen

14-Feb-08 23:19

Hi Prasanth, you replied to the wrong person.

Maxwell Chen