COM Discussion Boards

Re: Attach Method with SmartPointers causes problems marshaling UDTs?

5-May-06 3:34

No, I verified several times... The server is registered also in client machine (with /RegServer switch), but it's configured (via DCOMCNFG) to go ONLY remote. To be sure, I referred for my test to some image files there were present only on server machine, and I referred them putting down the entire path when calling server methods. If it was like that you are saying, I should get a "file not found" error, instead it did all that it had to do with no problems at all. Also, if I unplug network cable, I get a "RPC Server Unavailable" error.

Last question: if I decide not to use dual interfaces (therefore using IUnknown instead of IDispatch), can I get rid of this problem? If I decide doing custom marshaling where can I get an example of this technique (that I've never seen before?)

Thanx again....
Morenz

Roger Stoltz5-May-06 4:24

Roger Stoltz

5-May-06 4:24

Sorry Morenz, I haven't done custom marshalling so I cannot guide you in the howto process of custom marshalling.
However, I do know that with custom marshalling you can marshal any UDT you like since you have control of how it's done and transferred through the RPC channel.
I suspect that the howto-part is non-trivial and perhaps that might make you consider still using universal marshalling and automation interfaces.

If you're going for custom marshalling I guess you have to buy a good book about the subject... Sigh | :sigh:

--
Roger

It's suppose to be hard, otherwise anybody could do it!

Re: Attach Method with SmartPointers causes problems marshaling UDTs?

morenz5-May-06 4:30

Lookup installed com components

5-May-06 4:30

ok, no matter.

The final decision will be taken by the customer, and it will be based on how SOON they want the project Laugh | :laugh:

In the worst case (custom marshaling) I think I will buy a book and, why not, consider to give a shot in some serious forum, like this... Big Grin | :-D

Thanks for all.

Enjoy
Morenz
P.S. Pardon me, but in your footnote (or signature) you have a typo: you should have "It's supposed to be hard" instead of "It's suppose to be hard" Laugh | :laugh:

Hampus@foi3-May-06 21:57

Hampus@foi

3-May-06 21:57

Hey!

I was wondering if anyone knows of a way to lookup which com components are installed in Windows XP. I know I can look it up through Visual Studio but I don't want to install that on every system every time I want to check the installed com components.

Re: Lookup installed com components

Stephen Hewitt3-May-06 22:06

Stephen Hewitt

3-May-06 22:06

Look at the subkeys of "HKEY_CLASSES_ROOT/CLSID" in the registry.

Steve

Re: Lookup installed com components

Laxman Auti4-May-06 3:40

Laxman Auti

4-May-06 3:40

Hey good luck,

i have created the sample application for same

see the following code

//Initialise com libraries
	CoInitialize (NULL);

	//The Component Category Manager implemented by System
	//implements this interface
	ICatInformation *pCatInfo=NULL;
	
	//Create an instance of standard Component Category Manager
	HRESULT hr=CoCreateInstance (CLSID_StdComponentCategoriesMgr ,NULL,CLSCTX_INPROC_SERVER,IID_ICatInformation ,(void **)&pCatInfo);

	//Increase ref count on interface
	pCatInfo->AddRef ();

	//IEnumGUID interface provides enumerator for
	//enumerating through the collection of com objects
	IEnumGUID *pEnumGUID=NULL;

	//We are intersted in finding out only controls
	//so put CATID_Control in the array
	CATID pcatidImpl[1];
	CATID pcatidReqd[1];
	pcatidImpl[0]=CATID_Control;

	//Now enumerate the classes i.e. com objects of this type.
	pCatInfo->EnumClassesOfCategories (1,pcatidImpl,0,pcatidReqd ,&pEnumGUID);
	
	//Enumerate as long as you get S_OK
	CLSID clsid;
	while( (hr= pEnumGUID->Next( 1, &clsid, NULL ))==S_OK )
	{
		BSTR bstrClassName;	
	    

		//Get the information of class
		//This is what MSDN says about the parameters
		/*-----------------------------------------------
		USERCLASSTYPE_FULL     The full type name of the class. 
		USERCLASSTYPE_SHORT    A short name (maximum of 15 characters) that is used for popup menus and the Links dialog box. 
		USERCLASSTYPE_APPNAME  The name of the application servicing the class and is used in the Result text in dialog boxes. 
		-----------------------------------------------*/
		OleRegGetUserType (clsid,USERCLASSTYPE_FULL,&bstrClassName);
		CString strControlName(bstrClassName);
		//Add string in our listbox
		m_list1.AddString (strControlName);
	}	

	//we are done so now release the interface ptr
	pCatInfo->Release ();

	CoUninitialize ();

Knock out 'T' from CAN'T
You 'CAN' if you think you 'CAN'
Cool | :cool:

ActiveX control and COM dll

csylesh3-May-06 2:23

csylesh

3-May-06 2:23

Can someone explain me the major differences between an ActiveX control
and a COM dll in the context of accessing it from a web page using some
script.

For example, I need to get the MAC ID of the machine from within a web
page. So I thought of developing a COM dll, pack it in a cab using
cabarc, and call the method from within a script in the OnLoad of the
page. Do I need to actually go for creating an ActiveX control instead
of developing the COM dll? Is there any problem with using a COM dll?
Is there any additional advantage in going for ActiveX instead of COM
dll? Infact both the approaches worked fine on my development machine
!!

Thanks in advance.

Re: ActiveX control and COM dll

Milton Karimbekallil4-May-06 5:33

Milton Karimbekallil

4-May-06 5:33

If you dont need any UI features, then ofcourse you can go for a simple com component. Activex is for putting UI stuff.

rgds..mil10

Types of DLL

Smith#2-May-06 23:40

Smith#

2-May-06 23:40

How many kinds of DLLs are there? one that we are able to use with VB, ASP ect. The one which we are able to use with C++ but not VB, Can we create a DLL that is not COM based, and use it in VB? And what kind of Dlls we find in the windows system directories? Can any one brief on it? Confused | :confused:

NULL

Re: Types of DLL

_AnsHUMAN_ 3-May-06 3:34

_AnsHUMAN_

3-May-06 3:34

For more information on dll's you can refer the bottom link
http://www.thevbzone.com/l_dll.htm#DLL%20TYPES

Vision is Always important and so is your ATTITUDE.
Wishes.
Anshuman Dandekar

Difference between static_cast and normal casting

NiceNaidu2-May-06 2:30

NiceNaidu

2-May-06 2:30

Hi,

In one of the code snippets i have seen this.
It looks something like this.

interface IA;
interface IB;

class CCOMTest : public IA,public IB
{//Some code here
}

Inorder to get the pointer to IA,
the code looks something like this
static_cast<IA*>this;
why static_cast ??
what happens if i do (IA*)this ???

can anybody clarify my doubt??

I am a beginner to COM.

Thanks in Advance.

Appu

Re: Difference between static_cast and normal casting

guestcat2-May-06 3:20

Re: Difference between static_cast and normal casting

2-May-06 3:20

this is available in this codeproject site itself.

visit : http://www.codeproject.com/cpp/static_cast.asp

^-^
@|@
- redCat

Stephen Hewitt2-May-06 15:59

Stephen Hewitt

2-May-06 15:59

"Normal casting" (a.k.a "C-style" casts) should be avoided. If you need to cast always use static_cast, const_cast, reinterpret_cast or dynamic_cast. There are many reasons, some of which are that with these "function-style" casts your cast is:
1. Explicit (in intent).
2. Visible.
3. Checked for safety by the compiler.

There are still many people who use C++ but, for one reason or another, use "C-style" casts: These people are making a mistake. If you've been a maintenance programmer for a few years and seen the havoc caused by vague (in intent) and hard to spot or grep for casts you will probably agree. Some people argue that the new casts are ugly. That is intentional: casting, in general, is an ugly and dangerous practice and more often then not indicates a design flaw in your code. Casts should be ugly.

Steve

Why Default Interface ???

NiceNaidu2-May-06 1:33

NiceNaidu

2-May-06 1:33

Hi All,

Can anybody explain the need of default interface in COM?
I am beginner to COM.

Thanks in Advance.

Appu

guestcat2-May-06 1:50

2-May-06 1:50

hi ,
i guess you are asking about IUnknown.
if so, this interface contains the 3 basic methods that are pillars of COM technology to work.
Interface is nothing but the abstract base class in c++.
it means that ultimately all components are required to implement these three methods and simply it is generalized in this IUnknown interface.. that's it

- cheers
redCat

^-^
@|@

NiceNaidu2-May-06 2:18

NiceNaidu

2-May-06 2:18

Thanks for the immediate response.
But my doubt is different.

if we look at the idl file that is generated in a COM application we could find something like this.
[default] interface ICOMSample;

Will this [default] be associated with all interfaces. if not, why??
and What is the need of this.

Appu

Mike Dimmick2-May-06 2:44

Mike Dimmick

2-May-06 2:44

[default] is an indicator to scripting languages such as VBScript which interface is the default one. Such scripting languages cannot navigate to alternate interfaces, so in effect they can only access the single interface marked [default]. This attribute is saved in the generated type library but doesn't otherwise affect the generated code.

Visual Basic 6.0 can access non-default interfaces but this feature isn't commonly used. You simply create a variable of the interface type (e.g. Dim o As IOtherInterface) and assign an existing object to that variable - if the class implements that interface, VB assigns the variable, and if not, an error occurs. Similar behaviour occurs in .NET languages.

If all your clients are C++ clients you don't need to worry about this attribute.

Stability. What an interesting concept. -- Chris Maunder

guestcat2-May-06 3:01

GetRecordInfoFromGUID returns 0x80029C4A

2-May-06 3:01

using the [default] attribute, we are specifying that this interface is to be returned for the client by default at the time of creating object using the ProgID.

let us say the scripting client create an object for MSXML Parser using the CreatObject("Microsoft.XMLDOM") method.
by default IXMLDOMDocument interface is returned. here is where we can realize the use of this
[default] attribute.

there cannot be many [default] keywords.. one for incoming and one for outgoing interface is allowed that's all . also if you are not specifying anything, by default the first thing is taken.

^-^
@|@
- redCat

morenz2-May-06 0:07

Re: GetRecordInfoFromGUID returns 0x80029C4A

2-May-06 0:07

Hi folks,

I'm developing a DCOM Client/Server project under Win2000 SP4 (both client and server) with VC++ 6.0.

An object in this project has to interface with National Instruments Vision Builder 7, which DLLs are registered under \system32 folder (the package works with no problem)

In this object, I have to pass an UDT that is a struct containing a safearray of another struct and two integer (that is, the safearray contains the RGB Values of all the points of my image and the two integers keep the image size). These structures are shown below.

When I compile, I get MIDL warning 2368: Could not set UUID ... etc etc etc... but I've seen that this can be ignored with no problems.

Now, when I run both client and server, I get an error when preparing to pack the safearray. In facts, I call GetRecordInfoFromGuids to build my SafeArray with VT_RECORD. Before, I was not doing error checking and everything seemed to be alright, but I got crashes. Now, that I added an if (FAILED(hr)) statement just after the call, I get a 0x80029C4A value, that is "Cannot load type library/DLL".

Here's the structs:

		typedef <br />
		[uuid(394143BC-4672-4E14-85DB-A96EBCA5A417),<br />
		 version(1.0),<br />
		 helpstring("RGB Representation of a single point")]<br />
		struct RGBValue_struct {<br />
			unsigned char B;     //The blue value of the color.<br />
			unsigned char G;     //The green value of the color.<br />
			unsigned char R;     //The red value of the color.<br />
			unsigned char alpha; //The alpha value of the color, which represents extra information about a color image, such as gamma correction.<br />
		} RGBValue;<br />
<br />
<br />
	typedef<br />
//		{7F7037D8-C4D5-4b75-9C68-A9627EDE914B}<br />
		[uuid(7F7037D8-C4D5-4b75-9C68-A9627EDE914B),<br />
		version(1.0),<br />
		helpstring("IVA_Data COM Wrapper")]<br />
		struct COM_IVA_Data<br />
		{<br />
			SAFEARRAY(PointFloat)	saPoints;<br />
			int			numPoints;<br />
			int			pointIndex;<br />
		}COM_IVA_Data;

Here's the function call :

HRESULT Image2Variant (IVA_Image Source, COM_IVA_Image *Dest)<br />
{<br />
<br />
	HRESULT hr = 0;<br />
	// Initializing dimension descriptor for our SafeArray<br />
	SAFEARRAYBOUND sabRGB[2];<br />
<br />
	sabRGB[0].lLbound = 0;<br />
	sabRGB[0].cElements = Source.columns * Source.rows;<br />
<br />
	hr = SafeArrayDestroy(Dest->saPoints);<br />
	if (hr != 0)<br />
	{<br />
		sprintf(logMessage, "CAugVisionEngine - Image2Variant - SafeArrayDestroy Failed (%ld)",hr);<br />
		WriteLogFile(logMessage);<br />
	}<br />
	Dest->saPoints = NULL;<br />
	IRecordInfo *pUDTRecordInfo = NULL;<br />
	hr = ::GetRecordInfoFromGuids(LIBID_AugSvrLib, 1,0,0,RGBValue_IID, &pUDTRecordInfo);<br />
	if (FAILED(hr))<br />
	{<br />
		sprintf(logMessage,"GetRecordInfoFromGuids failed (0x%X). Invalid Argument.",hr);<br />
		WriteLogFile(logMessage);<br />
		return(-1);<br />
	}<br />
<br />
	Dest->saPoints = SafeArrayCreateEx(/*Dest->vt*/VT_RECORD, 1, sabRGB,pUDTRecordInfo);<br />
	if (Dest->saPoints == NULL)<br />
	{	<br />
		WriteLogFile("Image2Variant - Array Cannot be Created");<br />
		return (-1);<br />
	}<br />
	// First of all, we'll put columns & rows, that are not arrays<br />
<br />
	Dest->columns = Source.columns;<br />
	Dest->rows = Source.rows;<br />
<br />
	// Now, start (looooooooong) loop and put all values in array.<br />
	for (int i = 0; i < Source.columns*Source.rows; i++)<br />
	{<br />
<br />
		RGBValue TempValue = Source.array[i];<br />
		hr = SafeArrayPutElement(Dest->saPoints, (long *)&i/*lDimension*/, &TempValue);<br />
		if (hr != 0)<br />
		{<br />
		<br />
			WriteLogFile("SafeArrayPutElement failed!");<br />
			return (NULL);<br />
		<br />
		}<br />
	}<br />
	<br />
/*	Dest->saPoints = SafeArrayCreateEx(VT_RECORD, 1, sabRGB, pUDTRecordInfo);<br />
	hr = SafeArrayCopy(saRGB, &Dest->saPoints);<br />
<br />
		if (hr != 0)<br />
		{<br />
			switch(hr)<br />
			{<br />
			case E_INVALIDARG:<br />
				WriteLogFile("Invalid Destination SafeArray");<br />
				break;<br />
			case E_OUTOFMEMORY:<br />
				WriteLogFile("Out Of Memory");<br />
				break;<br />
			default:<br />
				WriteLogFile("Unknown Error");<br />
			}<br />
			return (NULL);<br />
		<br />
		}<br />
	WriteLogFile ("Returning OK");<br />
*/	return (S_OK);<br />
}

Here's the method prototype where I make the above function call:

In .IDL:
HRESULT loadImage([in]BSTR FileName, [out, retval]COM_IVA_Image *IVAImage);

In .H
STDMETHOD(loadImage)(/* [in] */ BSTR FileName, /* [out] */ COM_IVA_Image *IVAImage);

Here's what I verified:
1) The typelib is both on source and in executable folder (on both machines);
2) The DLLs are all under \system32 folder. I have moved none of them to my executable folder.
3) proxy/stub DLL is correctly registered in both machines
4)

I'm really stuck. I don't know what to do and I had to release project to customer 2 months ago...

Thanks in advance,
Morenz

Vibhash Jha3-May-06 2:35

Vibhash Jha

3-May-06 2:35

just a guess..
i have always seen iid name to be seen as class name..
RGBValue_struct_IID inplace of RGBValue_IID ....in ::GetRecordInfoFromGuids(LIBID_AugSvrLib, 1,0,0,RGBValue_IID, &pUDTRecordInfo);
if still problem persists ...need more info .. >>>>

cheers
vibhash

Re: GetRecordInfoFromGUID returns 0x80029C4A

morenz3-May-06 23:06

COM - ROT - Threading - moniker - RPC - Where is the problem?

3-May-06 23:06

hi,
thank you for the reply!

(un)fortunately, it was my fault, because I have currently 2 versions of this project (the MFC and the Service ones), that are slightly different, and I used the wrong type library...

Thanks again!

guestcat1-May-06 22:47