Re: function can't change a pointer's address

"Giovanni Dicanio" <giovanni.dicanio@invalid.it> ha scritto nel messaggio
news:OCFInchFIHA.2004@TK2MSFTNGP06.phx.gbl...


As a working code sample, you may find my code here to be interesting:

  http://www.geocities.com/giovanni.dicanio/vc/#cppdialog

There is a working C++ project that you can download, showing in code the
ideas I was trying to explain in my previous post.

There is an excerpt here (however, I think that you should consider the
original code, which is also full of comments).

----[ Dialog.h ]-------------------------------------------

<code file="Dialog.h">
class CDialog
{
public:
    ...

    // Shows the dialog-box.
    INT_PTR Show( HWND hwndParent = NULL );

    ...

protected:

    // Handle to dialog-box.
    // Derived classes can access it
    HWND m_hDlg;

    // Dialog-box procedure,
    // to be overridden by derived classes
    virtual INT_PTR Proc(
            HWND hwndDlg,
            UINT uMsg,
            WPARAM wParam,
            LPARAM lParam
        ) = 0;

private:
    ...

    // Global dialog-box procedure.
    // It routes messages to the instance-specific
    // dialog-box procedure.
    static INT_PTR CALLBACK GlobalProc(
        HWND hwndDlg,
        UINT uMsg,
        WPARAM wParam,
        LPARAM lParam
        );

};

</code>

----[ Dialog.cpp ]-----------------------------------------

<code file="Dialog.cpp">

INT_PTR CDialog::GlobalProc( HWND hwndDlg, UINT uMsg,
                             WPARAM wParam, LPARAM lParam )
{
    // Pointer to dialog class instance
    CDialog * theDialog = NULL;

    //
    // When we receive the WM_INITDIALOG message,
    // we store "this" class instance pointer into
    // dialog-box private slot (DWL_USER), so we can
    // retrieve "this" pointer in next calls, and route
    // the messages to instance-specific dialog procedure.
    //
    if ( uMsg == WM_INITDIALOG )
    {
        //
        // lParam contains the "this" instance pointer,
        // passed from ::DialogBoxParam.
        // Store this pointer into DWL_USER slot,
        // for retrieval in future.
        //
        ::SetWindowLong( hwndDlg, DWL_USER, (LONG) lParam );

        theDialog = (CDialog *)lParam;

        //
        // Save dialog-box handle into proper class
        // data member
        //
        _ASSERTE(hwndDlg != NULL);
        theDialog->m_hDlg = hwndDlg;
    }
    else
    {
        // Retrieve "this" instance pointer from DWL_USER slot
        theDialog = (CDialog *) ::GetWindowLong( hwndDlg,
                                                 DWL_USER );
    }

    // Route message to particular dialog-box instance
    if ( theDialog != NULL )
    {
        return theDialog->Proc( hwndDlg, uMsg, wParam, lParam );
    }
    else
    {
        // Default Windows message processing
        return FALSE;
    }
}

INT_PTR CDialog::Show( HWND hwndParent )
{
    _ASSERTE( m_hInstance != NULL );

    // Run the dialog-box
    INT_PTR result = ::DialogBoxParam(
        m_hInstance,
        MAKEINTRESOURCE( m_templateID ),
        hwndParent,
        CDialog::GlobalProc,
        (LPARAM) this
        );

    return result;
}

</code>

You can derive your class from CDialog, and add data members to store your
dialog state information. You must override the Proc() virtual method in
your derived class, and handle messages there (see the CTestDialog in sample
code).

This is how the code looks like in WinMain:

<code>
    // Testing dialog-box
    CTestDialog dlg( hInstance );

    // Set string to be shown to the user
    dlg.SetUserString( _T("<< enter text>>") );

    // Run the dialog-box.
    // (The user can modify the above string.)
    dlg.Show();

    // Retrieve and show user's string, if user pressed OK button
    if ( dlg.UserOK() )
    {
        ::MessageBox( HWND_DESKTOP, dlg.GetUserString(),
                _T("User entered:"), MB_OK );
    }

</code>

Giovanni