Re: Speed difference between CoCreateInstance and new operator - COM Discussion Boards

Re: What are the ways a COM dll can be used? + questions

19-Feb-09 21:23

But what does this mean?

#import "C:\Program Files\Common Files\System\ADO\msado15.dll"

Roger Stoltz19-Feb-09 21:53

Re: What are the ways a COM dll can be used? + questions

19-Feb-09 21:53

It means that you want to include type library information from the file.
Read more here[^].

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

grassrootkit19-Feb-09 21:30

Re: What are the ways a COM dll can be used? + questions

19-Feb-09 21:30

Also, my program has not generated any .tlh or .tli files. But it has created a C file with _i suffixed. like this : MyComTest_i.c. I should use this rather?
Using VC8.0.

Roger Stoltz19-Feb-09 21:57

Re: What are the ways a COM dll can be used? + questions

19-Feb-09 21:57

The extensions of the preprocessor generated files can be configured in the project settings. Different versions of MSVC seem to use different extensions.
Don't worry about the *.c-file. If you want to use the typelibrary information from another file, simply include the preprocessor generated header file.
A common way is to do the import in the stdafx.h file and then include the preprocessor generated header file as needed.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

grassrootkit19-Feb-09 22:43

Re: What are the ways a COM dll can be used? + questions [modified]

19-Feb-09 22:43

//You mean,In the project option, Configuration properties-> MIDL->Output->IID File = MyProject_i.c ?

I should use this file for using with client?

grassrootkit19-Feb-09 23:35

Speed difference between CoCreateInstance and new operator

19-Feb-09 23:35

Hey got it Smile | :)

.. I've used COM but not from a C++ client. So my first C++ client takes off well Big Grin | :-D

thanks.

Next is to use Connection points in a C++ client. Wink | ;)

Can you point to a good article that speaks about USING connection points in a C++ client?

modified on Friday, February 20, 2009 5:41 AM

Alexandre GRANVAUD19-Feb-09 3:08

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 3:08

Hi guys,
I have COM DLL Servers creating a lot of COM objects with CoCreateInstance and it's quite slow.
I wondered if replacing the CoCreateInstance(CLSID_Foo) by a new CComObject < CFoo > would speed up things ?
Or to be clearer, how slower is CoCreateInstance compared to new operator ?
thanks !

Roger Stoltz19-Feb-09 5:07

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 5:07

Alexandre GRANVAUD wrote:
I wondered if replacing the CoCreateInstance(CLSID_Foo) by a new CComObject < CFoo > would speed up things ?

No.
Since in both ways a COM object is created. Using the "new operator", as you call it, will eventually call ::CoCreateInstance(), so there's no difference.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

Alexandre GRANVAUD19-Feb-09 5:10

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 5:10

calling new CComObject < CThing > calls CoCoreateInstance????
i'm sure it doesnt !!

Roger Stoltz19-Feb-09 5:18

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 5:18

Alexandre GRANVAUD wrote:
calling new CComObject < CThing > calls CoCoreateInstance????
i'm sure it doesnt !!

No, of course; allocating memory for a CComObject doesn't call ::CoCreateInstance().
But in order to create the server you'd have to call CComObject::CreateInstance().
Otherwise the server won't be created and your comparison wouldn't make sense at all. Suspicious | :suss:

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

Alexandre GRANVAUD19-Feb-09 5:21

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 5:21

why do you need to call it ?
as i can see, the CCOmObject constructor call FinalConstruct, so what extra initialization do we need ?

CPallini19-Feb-09 5:10

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 5:10

You simply cannot use new to create COM objects (COM objects lifetime has its own rules Roll eyes | :rolleyes:

). If you need to create multiple objects, then you may obtain a speed enhancement using directly the IClassFactory interface, see the remarks section of this page [^].

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

[My articles]

Alexandre GRANVAUD19-Feb-09 5:11

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 5:11

yes you can in the same DLL, i do it everyday : in inprocess it's ok to do so Wink | ;)

new CComObject < CThing > then doing a Queryinterface or a AddRef on it and your object is ok

CPallini19-Feb-09 5:30

Re: Speed difference between CoCreateInstance and new operator

19-Feb-09 5:30

And what is the rationale behind that (other than revealing your bad practices Roll eyes | :rolleyes:

Alexandre GRANVAUD28-May-09 21:04

Re: Speed difference between CoCreateInstance and new operator

28-May-09 21:04

speed is always a good practice Wink | ;)

having a bad practice is ok if you know you have (i do Wink | ;)

) and know the consequences Wink | ;)

CPallini28-May-09 21:32

Re: Speed difference between CoCreateInstance and new operator

28-May-09 21:32

Alexandre GRANVAUD wrote:
speed is always a good practice

Before the first road accident Poke tongue | ;-P

--Carlo The Motor Biker.

(Anyway Carlo The Developer suspects it is more coding lazyness than speed improvement... Roll eyes | :rolleyes:

).

BTW breaking the COM object creation mechanism is really a bad practice and even if you're stuck with it, please don't tell other people to do it.
Smile | :)

Alexandre GRANVAUD28-May-09 21:46

Re: Speed difference between CoCreateInstance and new operator

28-May-09 21:46

lol i agree for the speed Wink | ;)

(but can't slowdown)
i don't break the com creation mechanism : the CreateInstance in a ClassFactory does exactly the same : a new CComObject<cthing> ! Wink | ;)

CPallini28-May-09 21:56

Know if a dll COM is registred or no!

28-May-09 21:56

Alexandre GRANVAUD wrote:
i don't break the com creation mechanism : the CreateInstance in a ClassFactory does exactly the same : a new CComObject !

Avoiding such call you're breaking it by definition. Of course you'll see the practical implications of such a wicked act just on 'strange' servers (i.e. servers that don't "do exactly the same", such a behaviour is allowed by COM).
Smile | :)

MrKBA19-Feb-09 2:42

19-Feb-09 2:42

hi,

Please, I developed an application with C + + and I need help; I am trying to test in my application that usually requires a COM + dll and I wonder how I could test that this dll is registred or no and it should display a message if this dll is not in the register or it does not exist?

thanks

D'Oh! | :doh:

CPallini19-Feb-09 2:49

19-Feb-09 2:49

What about calling CoGetClassObject [^]?
Smile | :)

MrKBA19-Feb-09 3:31

19-Feb-09 3:31

i just create an instance of a class in this dll and after i do a test if it is registred or no .this are some lines of code which can explain what i need exactly:

CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
hRes = TContext::CreateInstanceNoAppID(CLSID_TLibraryInformation_SeeEdbUI, &piLibInfoSeeEdbUI);
if(FAILED(hRes))
{
if(hRes == REGDB_E_CLASSNOTREG)
{
strTemp.LoadString(IDS_SEEEDBUIDLL_NOT_FOUND);
TErrorTool::DisplayErrorStack(TRUE, _bstr_t(strTemp));
}
else
{
strTemp.LoadString(IDS_SEEEDBUIDLL_NOT_FOUND);
TErrorTool::DisplayErrorStack(TRUE, _bstr_t(strTemp));
}
exit(0);
}

CPallini19-Feb-09 5:02

19-Feb-09 5:02

You don't you trust CoGetClassObject, do you? Why?
Smile | :)

MrKBA19-Feb-09 5:07

19-Feb-09 5:07

frankly, i don't try it and i would save the same structure of my code. so if you can help me with this?

CPallini19-Feb-09 5:14

19-Feb-09 5:14

I don't know Borland's (or CodeGear or whatever) classes so I cannot help with those.
I would keep the whole thing simple using directly COM library API, anyway, if your code is able to detect DLL's registration, that's fine, isn't it?

MrKBA19-Feb-09 6:35