But mmap() is not part of C++. For that matter, neither are file descriptors. So what you're really saying is that you want to use information that your particular implementation provides in an implementation-dependent way.
Which means that the answer to your question relies on the details of your implementation.
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...