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Using a VB based COM object from VC++

Posted on 1998-11-24
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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
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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 100 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.  
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