HOWTO: Use CreateObject with Visual C++ COM Objects

ID: Q192745

The information in this article applies to:

Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0

SUMMARY

This article explains how to use CreateObject with COM/ActiveX components created in Visual C++. The CreateObject programming syntax used to create an instance of a component created in Visual Basic may not work with a VC++ component, even though the object can be created using the New method. For example, assume you have an component named "neuLib" referenced in a Visual Basic project. The component has one createable object (Interface) named "myclass." The following code will work if the ActiveX component was created using either Visual Basic or Visual C++:


   Dim objNeu as neuLib.myclass
   Set objNeu =  New neuLib.myclass

However, the code below will work only for a component created using Visual Basic:


   Dim objNeu as neuLib.myclass
   Set objNeu = CreateObject("neuLib.myclass")

If this is a VC++-created component, you will receive the error message:

"Error 429. ActiveX component can't create object."

The reason CreateObject works with a Visual Basic component and not with a Visual C++ component can be explained and resolved by examining the different way in which Visual Basic and Visual C++ create program IDs (ProgID.) When you use CreateObject, the argument you provide is a ProgID. Visual Basic and Visual C++ assign a name to the ProgID differently. Visual Basic uses the original name, Visual C++ does not. In a Visual Basic component, the ProgID for this example is "neuLib.myclass." In a Visual C++ component, the ProgID would be "myclass.myclass.1," which requires the (correct) syntax:


   Dim objNeu as neuLib.myclass
   Set objNeu = CreateObject("myclass.myclass.1")

MORE INFORMATION

There are two ways to determine the ProgID that you need to specify when using CreateObject for the VC object.

Use the OLE/Com Viewer. If you have this utility installed, start it and open the Visual C++ component. From the View menu, select Expert Mode. Select "All Objects" from the list in the left portion of the window. Scroll until you find the name of the class, then and click it. The detail window on the right should display the information about the class; the ProgID will be listed with this information, and will look like:
```
      ProgID = myclass.myclass.1
 
```

Use the Registry Editor (Regedit.exe). Click on the Start button and select Run. Type "Regedit" and click OK. From the Edit menu in Regedit, choose Find. Enter the name of the class, and make sure that "Data" is the only check box selected. Click OK.

It is difficult to provide exact instructions for searching the Registry. The entry you are looking for will probably be the second one that is found (press the F3 key to resume searching.) When the data for the key is found, look in the window on the left half of the Regedit screen. If the tree node that is open says "ProgID," and the data in the window on the right contains the class name, then this is the value you want to use as the argument for CreateObject.

Additional query words: kbDSupport kbDSD kbVBp kbVBp500 kbVBp600 kbCtrl kbActiveX kbCOMt

Keywords : kbGrpVB
Version : WINDOWS:5.0,6.0
Platform : WINDOWS
Issue type : kbhowto