Re: Conditional compilation in Ada?

[Martin Krischik <martin@krischik.com>]

jtg wrote:

> I am using Ada for many years now, but recently
> I stumbled upon a problem I cannot solve: I need
> some kind of conditional preprocessing, which is
> commonly used in C programs:
> 
> #ifdef CONDITION
>   (some source code)
> #else
>   (other source code)
> #endif
> 
> How to achieve it with Ada?

Depends on the Ada compiler you use. GNAT has "GNAT PREPROCESS" or
"gnatprep" for short. You need to RTFM ;-) on how to use "GNAT PREPROCESS".

> I am developing two applications which are very similar
> and share the same source code. The only difference is
> a small change in a fundamental data structure. Both versions of the
> data structure are mostly handled the same way (within thousands of
> lines of source code), but there are some 10 or 20 (number still
> growing) places where minor changes are necessary. What is worse,
> during the development every several hours I have to prepare
> and run both the applications. To do this, I have to perform
> "human preprocessing": find those places, comment lines
> for app1, and uncomment lines for app2. This is very error prone and
> I have already made a mistake.
> 
> Any hints?

Well in AdaCL long ago I used "GNAT PREPROCESS" - however once I learned the
Ada way more closely I removed all use "GNAT PREPROCESS" and used the build
management instead:

All differences where encapsulated in private "XXX.Low_Level" packages. When
suitalble "pagama Inline" was uesd. Those packages where moved ito "NT",
"Linux" and "OS2" directories. The build mamagement picks up the version
needed.

With Regards

Martin

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