Writing Bug-Free C/D Code

[Henning Hasemann]

On Mon, 19 Mar 2007 14:20:31 +0000 (UTC)
Knud Soerensen <4tuu4k002 at sneakemail.com> wrote:

> Well, I think your problems is due to fundamental errors in your
> programming method. :-)
> 
> We all know the ordinary form of Hungarian notation as described in
> http://www.duckware.com/bugfreec/chapter3.html#naming
> but there is also a stronger form called app-Hungarian notation
> where the prefix gives a hint of the purpose for the variable.
> Like rowPos for a row position and colPos for a column position.
> Now it is easy to spot buggy code like rowPos=colPos etc.

I always name my variables like this. Personally I event tend to
not use such shortcut-names as they sometimes tend do be misleading
and hard to read. (row is clear, but later you might come to a point
where you or someone in your project uses column because he thinks its
short enough and so on).
Also this has nothing to do with my problems, because my problem is
not that I adding things together that have nothing to do with
each other, but adding things together that *have* to do with
each other but are often of different signedness.
 
> Using a type system we can take the idea a step further.
> 
> typedef int ROWPOS;
> typedef int COLPOS;
> 
> foo 
> {
>   ROWPOS rowPos;
>   COLPOS colPos;
>  
>   rowPos = colPos; // error at compiler time.
> }

Yeah sometimes I tend to this too,
but not for preventig errors like rowPos = colPos (as the
naming you suggested helps me enough). 
But I also try to be careful
not to have too much typedefs and/or aliases (yes I know the difference)
to trivial types such as int as it might confuse a reader
that assumes something special or magical beyond this.

> So, the fundamental flaw is that you use raw types instead
> of making a type for each purpose in your code.

Are you really sure it is a good idea to have a typedef for each purpose?
So a point struct would look like this for you:

typedef int COORD;
struct Point {
  COORD x, y;
}

right?

Dont get me wrong, I dont want to criticize this way of doing things
its just I never done it so much before because I am not sure
it is such a good idea.

> Could the compiler do something about it ?
> Yes, it could provide a switch called -bugfree 
> which trows a error every time a non user defined type is
> used in the code.

C'mon, that would be silly.

> It would also be useful if we could add an invariance to the type
> instead of have to change it into a class or structure.

You mean something like
typedef ubyte DiceResult;

DiceResult.invariant {
   assert(1 <= value);
   assert(value <= 6);
}

... would be handy sometimes, I agree. 

Henning

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