Re: Implementing C/C++ style #include...

[Andrew Berg <andrewb@votehere.net>]

Robert A Duff wrote:
> 
> Pascal Obry <p.obry@wanadoo.fr> writes:
> 
> > I agree with you that in such a case a preprocessor could be usefull. Anothe
> > way to handle this is by writing a template and have the right spec generated
> > by a script.
> >
> >    function Ada_Size_Of_Input is new
> >       Interfaces_C_More.Storage_Unit_Size_Of (Input_Type);
> >    pragma Export (<OS_CONVENTION>, Ada_Size_Of_Input,
> >                   "ball_ct633_ada_size_of_input",
> >                   "ball_ct633_ada_size_of_input");
> 
> Your "script" is, in fact, a macro preprocessor.
> 
> Are macros more or less evil than #if things?
> I've heard both opinions in this thread.  ;-)

As a full time C++ programmer, I'm going to have to side with Pascal
here.  Textual macros are dangerous, but a limited form of dangerous.  

#if's on the other hand are quite possibly the worst form of evil
imaginable, in that it is never really possible to know exactly what is
going on.  Even in simple cases it is bad, because when maintenance
happens they always get worse.  I suppose that if you are writing code
that will never get looked at they might not be so bad, but I have never
had that luxury.

Probably the only decent application of #if is '#if 0' as a way to
comment out multiple lines of code at once.  C's /* */ comments cannot
be nested and it gets really tedious to put //'s everywhere, so #if 0 is
a useful construct.

If you want an example of the kind of hell I am thinking of, go download
'stlport', a reasonably portable, reasonably compliant version of C++'s
STL.  Look at those header files for a while...

-andrew