?
Solved

Using a VB based COM object from VC++

Posted on 1998-11-24
4
Medium Priority
?
260 Views
Last Modified: 2013-11-25
I have a COM object available as a DLL.  The COM is authored in VB.  How do I incorporate this COM object into VC++?  
My code looks something like this:

struct IDB: public IUnknown
{
   STDMETHOD_(void, OpenDB) () = 0;
   STDMETHOD_(char*, ErrorMsgOut) () = 0;
};

static const IID IID_IDB =
{ 0x06122e34, 0x82ba, 0x11d2, { 0xbc, 0xc4, 0x00, 0x60, 0x97, 0x50, 0xcb, 0x8d } };

funct(void)
{
   CLSID clsid;
    LPCLASSFACTORY pClf;
    LPUNKNOWN pUnk;
    IDB* pDB;
    HRESULT hr;

    if ((hr = ::CLSIDFromProgID(L"Histo.ClsHisto", &clsid)) != NOERROR) {
        TRACE("unable to find Program ID -- error = %x\n", hr);
        return;
    }
    if ((hr = ::CoGetClassObject(clsid, CLSCTX_INPROC_SERVER,
        NULL, IID_IClassFactory, (void **) &pClf)) != NOERROR) {;
        TRACE("unable to find CLSID -- error = %x\n", hr);
        return;
    }

    pClf->CreateInstance(NULL, IID_IUnknown, (void**) &pUnk);
    pUnk->QueryInterface(IID_IDB, (void**) &pDB); // All three
    pDB->OpenDB();
    char * msg = pDB->ErrorMsgOut();

    pClf->Release();
    pUnk->Release();
    pDB->Release();
 
    AfxMessageBox(msg);
}

Is this the best way to do this?  I get pointers to the interface but the functions (OpenDB, GetMsg) don't execute. I'm not sure I'm using the correct GUID for the interface.  I'm using the ID for the class within the  object.  I'm a little confused on which registry values to use.
Thanks,
Jeff
0
Comment
Question by:sieglej
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
4 Comments
 
LVL 86

Expert Comment

by:jkr
ID: 1178575
The best way is opening the ClassWizard, selecting 'New Class' and choose 'From TypeLib'. Then, supply your dll as the source for the type library, and VC++ should generate the necessary wrapper classes...
0
 
LVL 86

Expert Comment

by:jkr
ID: 1178576
Ooops, sorry, i have been a bit on the MFC path...
Well, usually VC uses IDispatch, which is usually created like this:

    sc  =   ::CoCreateInstance  (   clsid,  
                                    NULL,
                                    CLSCTX_SERVER,
                                    IID_IDispatch,
                                    ( void**) &pDB
                                );

then, the methods are usually called using the 'Invoke()' method of an IDispatch.
If you have a _real_ COM interface (different from IDispatch), the IDL code could be helpful...
0
 
LVL 15

Accepted Solution

by:
Tommy Hui earned 200 total points
ID: 1178577
Alternatively, you can #import "vbcom.dll" and use the generated classes. The generated classes have member functions you can call that will either use IDispatch or vtable methods.
0
 

Author Comment

by:sieglej
ID: 1178578
Do you have an example of using #import in VC++?  All I have provided to me is a DLL file.  
0

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

When writing generic code, using template meta-programming techniques, it is sometimes useful to know if a type is convertible to another type. A good example of when this might be is if you are writing diagnostic instrumentation for code to generat…
A theme is a collection of property settings that allow you to define the look of pages and controls, and then apply the look consistently across pages in an application. Themes can be made up of a set of elements: skins, style sheets, images, and o…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.

719 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question