C# Definition:

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
class PRINTER_DEFAULTS {
   public string pDatatype;
   public IntPtr pDevMode;
   public uint DesiredAccess;
}

VB Definition:

Structure PRINTER_DEFAULTS
   Public pDatatype As IntPtr
   Public pDevMode As IntPtr
   Public DesiredAccess As Integer
End Structure

User-Defined Field Types:

None.

Notes:

PRINTER_DEFAULTS should be defined as a class instead of a struct, so that OpenPrinter does not need pDefaults to be passed in as a ref argument, thus you can pass in null if you want to.