CODEWITHSUNDEEP
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Akajit Saelim
Akajit Saelim

Reputation: 91

How to use CoCreateInstance in c++

I am a COM beginner. I have a DLL file that I register using the regsvr32 command. In the COM client, I try to use the CoCreateInstance function, but it doesn't work. This is my code:

IMessageBox *pBox;        
hr = CoCreateInstance(
          __uuidof(IMessageBox),
          NULL,
          CLSCTX_INPROC_SERVER,
          IID_IUnknown,
          (void **)&pBox
     );

IMessageBox is the interface which is defined in my DLL file. It implements the IDispatch interface. The result of hr displays the error REGDB_E_CLASSNOTREG. How do I use the CoCreateInstance function?

Upvotes: 2

Views: 1752

Answers (2)

David Heffernan
David Heffernan

Reputation: 612934

Well, the error tells you what is the problem. The class you are requesting is not registered in the COM registry. It could be that the IID of class that you registered is not the one that you are requesting. Another common failure mode is that you registered a 32 bit DLL and your calling process is 64 bit. Or vice versa.

Upvotes: 2

Frerich Raabe
Frerich Raabe

Reputation: 94319

Instead of __uuidof(IMessageBox) you have to pass the UUID of the class you want to instantiate - i.e. the class you registered previously using regsrv32.

Upvotes: 4

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