PRB: Unhandled Exception Using COM Smart Pointers with VC++

MORE INFORMATION

Steps to Reproduce Behavior

This problem can appear in any call in which a Component Object Model (COM) smart pointer is reused. The following example reproduces the problem:

   try {

        _SessionPtr pSession("MAPI.Session");
        pSession->Logon();

        FolderPtr   pFolder = pSession->Inbox;
        MessagesPtr pMessages = pFolder->Messages;
        MessagePtr  pMessage = pMessages->GetFirst();
        _bstr_t body;

        while (pMessage != NULL) {
            body = pMessage->Text;
            _tprintf("%s\n", (LPCTSTR)body);
            pMessage = pMessages->GetNext();
        }

    } catch (_com_error &e) {
        dump_com_error(e);
    }
				

The preceding code fails on the following line because you are now reassigning the smart pointer without first releasing the underlying object:

   pMessage = pMessages->GetNext();
				

For the preceding code to work, that line should be replaced by the following two lines of code:

   pMessage = NULL;
   pMessage = pMessages->GetNext();
				

It is also a good idea to set the pointers to NULL at the end of your code. This must be done if you are going to call the CoUninitialize function in the same scope as the smart pointers.