[vtk-developers] VTK style ques. - enum vars

[David Gobbi]

Hi Dean,
 
 I don't think that enums can be #undef'd, but it
 certainly is true that a #define will overrule an enum.
 Here is an example:
 
 [in the widget header file...]
 enum { LEFT_BUTTON = 1 };
 [and then in a header file included in the widget .cxx file...]
 #define LEFT_BUTTON 0
 
 The problem is that, after the preprocessor has seen the
 #define statement, it will replace every instance of
 LEFT_BUTTON with 0.  Preprocessing occurs before
 compilation, so the compiler proper will never even see
 LEFT_BUTTON.
 
 In other words, just because an enum is a member of
 a class or namespace, that doesn't protect it from being
 silently overruled by a #define.
 
 So, definitely, enum constant names should prefixed
 with "VTK" in order to protect them from conflicts.
 
  - David
 
 

----- Original Message ----
From: Dean Inglis <dean.inglis at sympatico.ca>
To: vtk-developers at vtk.org
Sent: Monday, September 18, 2006 9:39:05 AM
Subject: [vtk-developers] VTK style ques. - enum vars

with regard to this vtkusers message thread:

http://public.kitware.com/pipermail/vtkusers/2006-September/087016.html


it appears that at least 1 user has experienced
this problem with a conflict between #defines of
LEFT_BUTTON, RIGHT_BUTTON, MIDDLE_BUTTON
in the MFC afxctl.h file and the (protected) enum vars
in vtkImagePlaneWidget.h:
   enum
   {
   LEFT_BUTTON = 1,
   RIGHT_BUTTON = 2,
   MIDDLE_BUTTON = 3
   };

It was news to me that enums within a class are treated as
#defines and can therefore be #undef(ined) (please correct
me if I'm wrong!).  As a question of style, is there any
objection/problem to changing the above enums to say
   enum
   {
   VTK_LEFT_BUTTON = 1,
   VTK_RIGHT_BUTTON = 2,
   VTK_MIDDLE_BUTTON = 3
   };

thanks,
Dean

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