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What is CoCreateInstance and
What is deifference between CoCreateInstance and CoCreateInstanceEx. Pls Explain?
Thank you CodeProject
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Santosh Kumar79 wrote:
CoCreateInstance
CoCreateInstance[^]
Santosh Kumar79 wrote:
What is deifference between CoCreateInstance and CoCreateInstanceEx
See Remark [^]
"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow
cheers,
Alok Gupta
VC Forum Q&A :- I/ IV
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Perhaps more information on the nuts and bolts of how one actually *writes* this software may be helpful.. I have a step-by-step DCOM tutorial, where I build a simple server which says "Hello, world!" back to the client, may help put some of this in practical perspective...
The tutorials are written as a series of separate articles, called Steps, which cover the major breakpoints in the development of the system.
Step 1 of the tutorial for VC 6 is at
http://www.codeproject.com/com/HelloTutorial1.asp[^]
And Step 1 of the turtorial for Visual C++.NET 2003 is at
http://www.codeproject.com/useritems/HelloTutorial1NET.asp[^]
I tried to write the tutorials in Microsoft-ese, so you can follow along as if you were reading the Scribble tutorial. The VS.NET version is still a work in progress; that's why it's still in "Unedited User Constributions."
Not all the Steps have been written for the VS.NET version yet. But I am working on it!
Stay tuned!
Sincerely Yours,
Brian Hart
Department of Physics and Astronomy
University of California, Irvine
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Hi, Some one can help/guide me how to debug the COM C++ DLL. I built both DLL and EXE, which is using this DLL, in debug mode. My main COM/MFC application (EXE) loads/uses this DLL. I tried specifying my executable in "Project Settings -> Debug -> General -> Executable for Debug session" of COM C++ DLL project and with putting breakpoint in DLL. But unfortunately the execution didn't stop at my breakpoint and continues to execute my application.
Any help will be appreciated in this regard.
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Make sure you are in "DEBUG" mode. And that the debug version of your dll not the release verions is registered.
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Hi ,
I have developed one dll and it is working fine in debug build however it is giving me following below error in ReleaseUMinSize build. Can you help me to resolved this issue.
Linking...
Creating library ReleaseUMinSize/PLUManager.lib and object ReleaseUMinSize/PLUManager.exp
LIBC.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
ReleaseUMinSize/PLUManager.dll : fatal error LNK1120: 1 unresolved externals
Thanks
Pankaj
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Excel enables the creation of user-defined functions that can be used in Excel formulas. So I use these code to create a COM introp.
-------------------------------------------------
using System;
using System.Runtime.InteropServices;
using Microsoft.Win32;
namespace AutomationAddin {
[ClassInterface(ClassInterfaceType.AutoDual)]
public class MyFunctions {
public MyFunctions() {
}
public double MultiplyNTimes(double number1,
double number2, double timesToMultiply) {
double result = number1;
for (double i = 0; i < timesToMultiply; i++) {
result = result * number2;
}
return result;
}
[ComRegisterFunctionAttribute]
public static void RegisterFunction(Type type) {
Registry.ClassesRoot.CreateSubKey(
GetSubKeyName(type));
}
[ComUnregisterFunctionAttribute]
public static void UnregisterFunction(Type type) {
Registry.ClassesRoot.DeleteSubKey(
GetSubKeyName(type), false);
}
private static string GetSubKeyName(Type type) {
System.Text.StringBuilder s =
new System.Text.StringBuilder();
s.Append(@"CLSID\{");
s.Append(type.GUID.ToString().ToUpper());
s.Append(@"}\Programmable");
return s.ToString();
}
}
}
-----------------------------------------------------
And set project build property,checked output item,register COM interop.
Building the project,that's success.
Launch Excel and choose Add-Ins from the Tools menu to display the Add-Ins dialog. In the Add-Ins dialog, click the Automation button. But I can't find the class I created by looking for AutomationAddin.MyFunctions in the list of automation servers.
What's wrong? Please help me !Thanks,by the way,My development tool is VS2005 ,Office 2003 (sp2)simply chinese.
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We have a product that does the following:
* starts up as service
* spawns of n threads that actually do work. All of these threads do the same thing, which is to automate a COM server to produce a result.
After about 1000 transactions have run through the process, it starts to get the hexadecimal value above as a return code. This is not always the case, and the error is in fact quite intermittent.
The call that fails is a very simple call on a smart pointer to a home-grown DCOM object.
Anyone run into this before? Any thoughts?
My first instinct is that it's one of those bizarre interplays between threads and memory and that at some point some thing just loses it's mind (very technical, I know 
Thanks. 
Also, please forgive me if this should be in the threading forum. I thought I'd start here since I KNOW that COM is involved, and only suspect threading.
Joe Hayes
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Well, if the return code could be interpreted as an error code it would be CO_E_OBJNOTREG meaning that the object is not registered.
I suspect that the smart pointer call creates an object, or in this case tries to create an object.
Hope this helps
--
Roger
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I've had a similar problem before, if I remember right it was an issue with following the rules about who (which thread) is making the calls. I'd make sure that your following the interface marshalling rules. If I remember right in my case it was somebody creating the object in one thread then making calls in another without having marshalled the interface. Hope that helps.
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Hi All,
Info: this is a single class object
why this fails?
IF I USE THIS:
hr = CoGetClassObject(CLSID_CoCar, CLSCTX_INPROC_SERVER, NULL,
IID_IClassFactory, (void**)&pCarFact);
hr = pCarFact->CreateInstance(NULL, IID_ICreateCar, (void**)&pICreateCar);
IT COMPILES BUT IT CRASHES if I insist to use IClassFactory::CreateInstance...
.................................
Then I replace it with
hr = CoCreateInstance(CLSID_CoCar, NULL, CLSCTX_INPROC_SERVER, IID_ICreateCar,
(void**)&pICreateCar);
IT COMPILES AND IT RUNS...
Still researching why but no answer so far...
TIA for any help 
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Did your CoGetClassObject API Succeeded ? what is the HR value after CoGetClassObject API call ?
AFAIK, CoCreateInstance internally uses CoGetClassObject API and queries for class Factory.
If possible post your code snippet.
Have a great day ahead!
Regards,
Sohail Kadiwala
(My Blog - http://blogs.wdevs.com/sohail/[^])
modified 21-Apr-21 21:01pm.
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odiesback wrote:
IT COMPILES BUT IT CRASHES if I insist to use IClassFactory::CreateInstance...
Too complicated to go into.  You need a good book on COM etc...
A better question is why do you not want to just use the first syntax???
odiesback wrote:
Then I replace it with
hr = CoCreateInstance(CLSID_CoCar, NULL, CLSCTX_INPROC_SERVER, IID_ICreateCar,
(void**)&pICreateCar);
This works because CoCreateInstance gets the factory for you behind the scenes, i.e.
CoCreateInstance first calls hr = CoGetClassObject(...factory parameters...)
Then it calls hr = pFactory->CreateInstance(...class parameters ...)
and returns the class pointer as hr.
The only real difference between the two approaches is convenience and performance.
When you call CoCreateInstance, COM gets the factory, and gets the class for you - it does all the work behind the scenes, and is convenient. But if you make multiple calls to get multiple instances of class from the same factory, COM may (or may not be, depending on a lot of things) recreating the same factory multiple times.
If you know in advance that you will be creating numerous instances of the same class objects from a specific factory, or if you know in advance that you will be creating different classes that are all supplied by a specific factory, then you can get the pointer to the factory yourself, hang on to it, and call pFactory->CreateInstance(...) directly.
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Thanks for your repplies:
I am studying COM from "Developer's Workshop to COM and ATL 3.0"
and the code in question is presented by the author for VC6.0 and I am
using VC7.0.
The book uses the call to the IClassFactory and then calls CreateInstance(), which
refuses to run. After trying go get it to work I replace for a call
to CoCreateInstance(). Not even the code supplied by the CD aruns.
this is the code:
----------------------------------------------------
#include <iostream.h>
#include "interfaces.h"
#include "iid.h"
int main()
{
// Initialize COM sub system
CoInitialize(NULL);
// Declare all interfaces you are going to use
IClassFactory* pCarFact = NULL;
ICreateCar* pICreateCar = NULL;
IStats* pIStats = NULL;
IEngine* pIEngine = NULL;
// Declare the return type HRESULT
HRESULT hr;
// Screen page Header
cout << "\n*****************************************************";
cout << "\n** T H E A M A Z I N G C O C A R C L I E N T **";
cout << "\n*****************************************************\n\n";;
// Grab the IClassFactory pointer from CoCarFactory
hr = CoGetClassObject(CLSID_CoCar, CLSCTX_INPROC_SERVER, NULL,
IID_IClassFactory, (void**)&pCarFact);
hr = CoCreateInstance(CLSID_CoCar, NULL, CLSCTX_INPROC_SERVER, IID_ICreateCar,
(void**)&pICreateCar);
//-------> hr is 0 coming out of the expression above
/*
 // THE PROGRAM COMPILES BUT IT CRASHES IF USING the IClassFactory pointer
// Call CreateInstance() from the Class Fatory pointer, and ask for IID_ICreate from the
// CoCar
hr = pCarFact->CreateInstance(NULL, IID_ICreateCar, (void**)&pICreateCar);
// Once you used the CoClassFactory pointer, release it.
pCarFact->Release();
*/
// Exercise ICreateCar
if(SUCCEEDED(hr))
{
BSTR name = SysAllocString(L"Odie Silva");
pICreateCar->SetPetName(name);
SysFreeString(name);
pICreateCar->SetMaxSpeed(100);
// Find IStats
hr = pICreateCar->QueryInterface(IID_IStats, (void**)&pIStats);
// Now can release ICreateCar
pICreateCar->Release();
}
if(SUCCEEDED(hr))
{
// Display properties
pIStats->DisplayStats();
// Switch hr to IEngine interface using IStats* (can also use IUnknown*)
hr = pIStats->QueryInterface(IID_IEngine, (void**)&pIEngine);
}
// If successful run the IEngine
if(SUCCEEDED(hr))
{
int curSpd = 0;
int maxSp = 0;
pIEngine->GetMaxSpeed(&maxSp);
do
{
pIEngine->SpeedUp();
pIEngine->GetCurSpeed(&curSpd);
cout << "\n\n Speed is: " << curSpd << endl;
}while(curSpd < maxSp);
// Convert BSTR to char array
char buff[80];
BSTR bstr;
pIStats->GetPetName(&bstr);
WideCharToMultiByte(CP_ACP, NULL, bstr, -1, buff, 80, NULL, NULL);
cout << "\n" << buff << " has blown up! Lead foot!" << endl;
// Final clean up
SysFreeString(bstr);
if(pIEngine)
pIEngine->Release();
if(pIStats)
pIStats->Release();
}
// Unload COM system
CoUninitialize();
return 0;
}
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I just cant find out why my program is crashing.
I simplified it to track down the erro rand the only thing I can say
for sure is that it fails to create my object instance.
hr = S_OK coming out of CoGetClassObject
it crashes when debugging at CreateInstance() using the class factory pointer
"unhandled exception..."
I will check my imp of CreateInstance in my class factory but why it works
great if I use CoCreateInstance(), if that function is just a wrapper and
uses the same data I am using through the class factory?
Thanks for your help
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I am devlopping a control (a simple container (simple frame)using MFC, not ATL) and i need to receive all mouse events, client area and non-client area ones, when the control is selected on a form in the IDE of VB.
Does somebody can help me ?
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Hi lgaudouen,
SetCapture(HWND hWnd) and ReleaseCapture() API's would do the trick for you.
For more information on these API's, refer to the MSDN...
Hope this helps !
Cheers,
Vishal
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Hello, I'm very new to COM and just had a simple question.
Does CoCreateInstance() check to see if there is another instance already in existance?
I am currently using CoCreateInstance() to create my class object, but I only want to do it once.
I want to do this:
If (there is no instance)
then (CoCreateInstance())
else (run code)
Is this automatically done within CoCreateInstance or is there another way to check to see if an instance already exists? I want to avoid running CoCreateInstance() multiple times.
Thank you.
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How to write a com application in c# and deploy.
Any source please!
pkarunadheera
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you can reference to the book 'C# COM+ programming':->
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Hello.
I need to retrive a all Interfaces (methods) and propertyes from a certain COM object i dont know realy where to start...
I'm there aren't many sources exept for some Object Browsers but no sources 
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Hi benjamin23,
OLE/COM Object Viewer gives all inofrmation about the COM object. Go to "Type
Library" and double click the COM object you want, it would show you the
information about the interfaces/structures that COM object has...
Hope this would help you...
All the best !
Cheers,
Vishal
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The link has been verry userful, still leavme some cuestions:
supose i have an instance of "Word.Application"
I dont know if ".Visible" exists as a property or even a method, the same could happen to ".WebPagePreview" it's a method but my program doesnt know that i need to retrive the collection of methods and propertyes right before i create the object, this whay i can parse for example a .txt wich contains the methods to call or the variables to set.
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Hmmm.. I think you are looking for invoking/calling a method or property dynamically. With this assumption, I think the following interface will help solve your problem -
IDispatch
IDispatch has a method called as GetIDsOfName to which you pass the name of method and it will return you an ID. Using this ID you call another method of IDispatch, namely, Invoke. For more details please check MSDN documentation for IDispatch and its methods.
I hope this helps.
Let me know if you are looking for anything other than what I assumed.
Have a great day ahead!
Regards,
Sohail Kadiwala
(My Blog - http://blogs.wdevs.com/sohail/[^])
modified 21-Apr-21 21:01pm.
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