Re: How to put a struct into a VARIANT? - COM Discussion Boards

27-Sep-05 23:23

hi folks;)
I need to put a struct (in which i have another struct...) into a VARIANT to pass it between DCOM client and server methods.
I would like to avoid custom marshaling (i've never done it and the customer is getting angry... so I have no time to spend on it...).

How can I do?

Thanks in advance!
Morenz

GizzoF28-Sep-05 0:05

GizzoF

28-Sep-05 0:05

Maybe this could help`

http://www.mvps.org/vcfaq/com/4.htm[^]

morenz28-Sep-05 3:47

28-Sep-05 3:47

Hi,
First of all, thanks for your prompt reply!

Well, I can say that in 3 sheets of paper there's the informations I searched for days!

Only one thing, SafeArrayCreateEx function and VT_RECORD vartype are not declared in my Visual Studio 6. Can I get access to them installing service packs?

Many thanks, you're great!
Hope can help you back in future,
bye for now,
Morenz

Mike Dimmick28-Sep-05 5:09

Mike Dimmick

28-Sep-05 5:09

They are declared in my installation of Visual Studio 6. I'm using SP5. The easiest way to find out your service pack level is to launch Visual Basic, since the service pack number is included in the splash screen graphic.

Download service packs from here[^].

Stability. What an interesting concept. -- Chris Maunder

morenz29-Sep-05 1:27

29-Sep-05 1:27

Many thanks.
My problem was that I did not know if that new function was implemented in a later service pack or other stuff. Telling me that you have that function in your SP5 resolved me the problem, so I'm installing SP6 (that I had in the past, on the other computer).

OK, let's implement those final functions and make the customer happy! Wink | ;)

Thanks to everyone again!
Morenz

morenz30-Sep-05 0:36

30-Sep-05 0:36

Hello again...
it was too good to be real....

I used what that HOWTO said (implementing a struct into my IDL file, giving it a UUID and managing it with VARIANTs).

Now, I got a problem.
If I write in IDL
typedef [uuid(...)]
struct myStruct
{
...
...
...
}my;
, when I compile my project, MIDL is OK, but I get C2787 when compiling: no GUID has been associated with this object.

I tried to use, in IDL,
[uuid(....)]
struct myStruct
{
...
...
..
}my;
and now I get MIDL2072: inapplicable attribute: [uuid][Struct 'myStruct']

How can I get it compiled?
I'm going crazy!
thanx again!

-- modified at 6:37 Friday 30th September, 2005

morenz30-Sep-05 3:28

30-Sep-05 3:28

OK OK OK , I got the problem. I think.
Probably I need February 2003 Platform SDK (the last one released for VS 6.0).
I tried to compile that code with VS.NET 2002 and it worked.

Now the problem is to get that SDK, that is not downloadable anymore from Microsoft website... Frown | :(

I will search, in worst case I will order the CD....

Bye

Rory Solley29-Sep-05 0:49

Rory Solley

29-Sep-05 0:49

If you've written both client and server (and so can control alignment and other compile-time issues), you could create a common header file for both applications that contains the struct definition and then embed the data as a byte stream (VT_UI1|VT_ARRAY) in a VARIANT and pass that over (D)COM. I've used that method successfully in the past and its reasonably flexible.

morenz30-Sep-05 0:42

30-Sep-05 0:42

Hi!
What you're saying is to brutally force custom serialization
This should be a good method, but how can I declare my safearray dimension? With sizeof()? I've got some structs that has inside an array of another struct....

Thanks again...

Rory Solley30-Sep-05 4:10

Rory Solley

30-Sep-05 4:10

Yes, use sizeof(YourStruct). If you have embedded structs, you're going to have to be more creative e.g.

sizeof(YourStruct) + (sizeof(YourEmbeddedStruct) * NumberOfEmbeddedStructs)

etc.
It can get tricky if your structs contain "variable" data, such as strings. In the past, I've either defined the maximum size of the string (and therefore constrained the array inside the struct definition) or I've added a counter then a pointer, e.g.

...
unsigned long ByteCount;
unsigned char* pByteData;
};

The count tells the caller how big the variable data is. Hope that helps.

Jörgen Sigvardsson3-Oct-05 6:22

Jörgen Sigvardsson

3-Oct-05 6:22

Why do that, when you can define the structure in IDL? Unsure | :~

--
Look straight into the light!

Rory Solley3-Oct-05 22:20

Rory Solley

3-Oct-05 22:20

Yep, that's perfectly valid (and arguably the "right" way) but then you have an extra step of publishing the interface and managing proxy stubs. My way keeps things simple and flexible.

morenz4-Oct-05 3:09

Thorwing a event with a collection

4-Oct-05 3:09

Because my structs contain, in some cases, arrays, that have to be defined as SAFEARRAYS.

In any case, I implemented this way... I will debug the application when I will resolve my new problems (It's since a month that, when I manage to resolve a strange problem, there comes in another problem, even stranger, if possible! Sigh | :sigh:

)

If you're curious, look above.... Smile | :)

Thanks again,
Morenz

Customizing IE

babai27-Sep-05 20:52

babai

27-Sep-05 20:52

Hi,
I'm a newbie in COM development. I need to open a file of a particular format,other the ones supported by IE like .doc,.txt,.PDF etc, in the IE.
e.g. if the file is say, a.x, of a particular format, the "Open With : IE" will open the file in the IE browser window, much like the case of .pdf file.
I browsed a lot, such as, BHO etc. but could not find a proper solution.

So, I need this very urgently....

Regards,
babai.

-- modified at 12:37 Thursday 29th September, 2005

GizzoF27-Sep-05 7:53

GizzoF

27-Sep-05 7:53

I have a COM object that throws an event with a collection of others COM objects. I’m not sure about the way I have to do it. The code I have implemented is like....

ICollection * pInterfaceCollection;<br />
CCollection * pCollection = new CCollection (<COM objects array>);<br />
pCollection->QueryInterface(IID_ICollection, (void**) &pInterfaceCollection);<br />
pInterfaceCollection->Release();<br />
<br />
result = Fire_OnColletionItems(pInterfaceCollection);<br />
if(FAILED(result))<br />
{<br />
	... <br />
}

The problem here is that I have memory leaks. I fire the event, the client (an VB application) manages it, I shut down the client, and then I shut down my application (the server)... and there they are. I thought that the client was who release the object so I shouldn’t do it. How should I to do this?

Thank you in advance.

PD: sorry for my english

-- modified at 13:54 Tuesday 27th September, 2005

Mixing COM and non-COM property pages

DolphLundgren27-Sep-05 5:03

DolphLundgren

27-Sep-05 5:03

I'm working on an object that crosses two systems (one system uses standard CPropertyPages for all its objects, the other uses COM/ATL IPropertyPageImpl<t>)

The standard system objects simply create a property sheet and invoke DoModal() while the other uses OleCreatePropertyFrame() for its pages.

How do you launch a mixed collection of both systems? (CPropertyPages with COM/ATL ones)

Thanks in advance for advice!

Re: Mixing COM and non-COM property pages

Jörgen Sigvardsson27-Sep-05 9:56

Jörgen Sigvardsson

27-Sep-05 9:56

DolphLundgren wrote:
How do you launch a mixed collection of both systems? (CPropertyPages with COM/ATL ones)

I don't know exactly how CPropertyPages work, so maybe what I'm about to suggest is just not doable. If so, then I appologize.

I suppose you could inherit a new class from CPropertyPage, in which you host the COM property page, and mediates between the COM interfaces (IPropertyPage and IPropertyPageSite) and the CPropertyPage interface.

What you need to think about when creating the COM property page is:
* Your class based on CPropertyPage must implement IPropertyPageSite
* After you've created the IPropertyPage object, call SetPageSite(this)
* Give the COM object to the prop page object by using SetObjects()
* Then call Activate(m_hWnd, rcTheRectangle, FALSE)
* Followed by Show(SW_SHOW) (I think this is necessary - I don't remember - you'll notice)

IPropertyPageSite is straightforward to implement. Please refer to the MSDN docs.

Call the prop page object's Apply() method when suitable (probably on some well defined OnApply()-event defined for CPropertyPage).

When you are closing down the CPropertyPage window, call the prop page object's Deactivate() method.

--
Keep talking! You're the fool, I'm the preacher.

Dynamically switching between DLLs

Divick26-Sep-05 20:41

Divick

26-Sep-05 20:41

Hi all,
does any one know that how can I switch between two DLLs
dynamically based on some condition.

What I want to achieve is that I have an application which has to call
some functions in a C++ library exposed as a DLL.

Now I have two versions of this library which export the almost the
same symbols (not exactly the same thus different .libs for them) but I
want to allow the application to switch between these two DLL's
dynamically so that whenever it wishes it can call one library or the
other as per the need.

Remember I cannot link with both the libraries because they both
contain almost the same symbols. The sample scenario is shown below:

app --- links with EITHER DLL1
--- OR links with DLL2

DLL1 -- exports say symbols - a,b,c
DLL2 -- exports say symbols - b,c,d

app decides dynamically at runtime
if(condition 1)
Load DLL1
call a;
...
else
Load DLL2
call b;
call c;
...

I hope my question is clear.
Thanks in advance,
Divick

prasad_som26-Sep-05 21:18

prasad_som

26-Sep-05 21:18

cant you use LoadLibrary(),freelibrary() ?

Divick26-Sep-05 21:28

Divick

26-Sep-05 21:28

Well, to clarify my question more, I don't want to do a LoadLibrary within the application. What I want is that the application shouldn't know at all which DLL it is loading but there may be additional DLL or COM component in between which can decide which particular DLL to load and then load the DLL automatically.

Waiting for suggestions/ tips/ comments.
Thanks,
Divick

Divick27-Sep-05 20:47

Divick

27-Sep-05 20:47

Does nobody has a solution for this or my question is too cryptic?

Any suggestions/ideas are welcome.

Thanks a ton,
Divick