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Introduction

A dialog-based application by default will close when the user hits Return, Esc, File -> Close, or the "X" in the system menu (top right of dialog/window). If your app is complicated and doesn't have an OK and/or Cancel button in the main window of the app, the user may be surprised when he hits Return (or Esc) accidentally and the app closes on him. Imagine if you were using MS Word and it closed when you hit the "Return" key, especially if you hadn't saved hours of work. Pretty upsetting.

I wanted my app to close only when the user clicked the "X" in the system menu or selected the File-> Close (or Exit) menu item.

The solution is simple.

//Disable OnCancel 
void MyDialog::OnCancel()
{ 
} 

//Disable OnOK 
void MyDialog::OnOK()
{ 
}

//message map event handler executed when user selects the File Ext menu 
item
void MyDialog::OnFileClose()
{
    EndDialog(IDOK);
}

void MyDialog::OnSysCommand(UINT nID, LPARAM lParam)
{
    if ((nID & 0xFFF0) == IDM_ABOUTBOX)
    {
        CAboutDlg dlgAbout;   //if you have an about dialog

        dlgAbout.DoModal();
    }
    //add the following code
    else if ((nID & 0xFFF0) == SC_CLOSE)
    {
        //if user clicked the "X"
        EndDialog(IDOK);   //Close the dialog with IDOK (or IDCANCEL)
        //---end of code you have added   
    }
    else
    {
        CDialog::OnSysCommand(nID, lParam);
    }
}