Receiving an E-mail Message

Retrieving mail from your Inbox with CDO is also easy. Here is my illustration code (CDO/ReceiveMail):

void CReceiveMailDlg::OnReceive()
{
    try
    {
        // Initialize session object
        Session session;
        BOOL bResult = session.CreateDispatch("MAPI.Session");
        ASSERT(bResult);

        // Logon
        VARIANT vResult;
        VariantInit(&vResult);
        session.InvokeHelper(0x77, DISPATCH_METHOD, VT_VARIANT, (void *) &vResult, NULL);
        VariantClear(&vResult);

        // Get Inbox
        VARIANT vInbox = session.GetInbox();
        Folder Inbox(vInbox.pdispVal);
        ASSERT(Inbox.m_lpDispatch);

        // Get Messages collection
        VARIANT vMessages = Inbox.GetMessages();
        Messages messages(vMessages.pdispVal);
        ASSERT(messages.m_lpDispatch);

        // Get first message
        VARIANT vMessage;
        VariantInit(&vMessage);
        messages.InvokeHelper(0x6d, DISPATCH_METHOD, VT_VARIANT, (void *) &vMessage, NULL);
        Message message(vMessage.pdispVal);

        // Get subject
        VARIANT vSubject = message.GetSubject();
        CString strSubject(vSubject.bstrVal);
        VariantClear(&vSubject);

        // Get text
        VARIANT vText = message.GetText();
        CString strText(vText.bstrVal);
        VariantClear(&vText);

        // Display a message box with results.
        CString str = "Received message. Subject: " +
            strSubject + ". Text: " + strText + ".";
        ::MessageBox(NULL, str, "Success", MB_OK | MB_ICONINFORMATION);
        session.Logoff();

        // Cleanup
        message.ReleaseDispatch();
        messages.ReleaseDispatch();
        Inbox.ReleaseDispatch();
    }
    catch (...)
    {
        ::MessageBox(NULL, "Exception raised...", "Error", MB_OK | MB_ICONINFORMATION);
    }
}

The beginning is standard: I create the session and do logon to underlying MAPI. Then I open the Inbox, navigate to the Messages collection and obtain the first message in there (you must have at least one message in your Inbox for this code to work). Then I retrieve message subject and text and display them.

This code, as well as all other MFC examples in this chapter assume that COM is properly initialized. All these samples are trivial dialog based MFC applications. I have put the CoInitialize call before displaying the modal dialog and corresponding CoUninitialize after the DoModal call. Although the class collection in the project may at first seem quite rich, the following simple procedure had been used to create the app:

Create an MFC dialog based project.
Use ClassWizard to import classes from olemsg32.dll.
Add a custom button on the dialog and map a handler to it.
Add #include <afxdisp.h> to stdafx.h file.
Add CoInitialize(NULL) before displaying the dialog and CoUninitialize() after.
Add code to your handler as illustrated above.

Obviously, this demo code (and other samples for this book) lacks proper error handling. Thus, it is not acceptable for production. This is because the book's primary goal is to illustrate possibilities rather than making samples robust and inevitably less readable.

I have shown how you can use CDO with C++. The two ways that I have described in this chapter (either using IDispatch interface directly or ClassWizard generated COleDispatchDriver derived classes) require some knowledge of Automation (how to handle VARIANTs, for example). Although it is possible to cut and paste code from my or somebody else's samples, modify them slightly and make simple things working, it is unlikely that a serious CDO C++ development would be possible without familiarity with Automation. In this context, perhaps, one could find Visual Basic, and even Visual Basic Script to be better choices because the development platform handles the majority of problems.

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