Re: Predefining __OS_DOS__

[Peter Gerwinski <peter at gerwinski dot de>]

Jeffrey A Law wrote:
>   > Up to now, `MSDOS', `_WIN32' and `__EMX__' always occured in
>   > this combination in the GPC project.  Sometimes someone forgot
>   > one (or two) of them and caused unpleasant bugs.  I don't know,
>   > but I can imagine that similar things have happened in the C
>   > world, too.
> True.  This can be a problem.  But I'd prefer people to actually think about
> the code they write instead of depending on this kind of crutch.
> 
> I'd think it is just as likely that someone will start using __OS_DOS__ for
> code they think is common to dos-like systems, when in fact it is not common
> to all the dos-like systems.
> 
> Additionally, less and less code in the compiler should be conditional on
> host defines of this nature.  Instead we should be depending on autoconf
> macros and defines which indicate the availability or non-availability of
> specific features.  This is the general direction most FSF code is taking
> and __OS_DOS__ seems to me like a step backwards.

In most other cases I would agree, but ports of GNU software to
MS-DOS-like systems have always been somewhat special rather
than part of the main line.  These ports being all independent
resulted in independent, unsystematic predefinitions.  (There
are, for instance, also -D__MSDOS__, -D__WIN32__, -DWIN32, but
only the combination I mentioned has the intended effect of
identifying all MS-DOS-like systems.)  I think it's time to
clean them up, and a common predefinition for all MS-DOS-like
systems is a step forward in this direction.

BTW, does anyone know whether autoconf works on MS-DOS?

>   > This is confusing for Pascal programmers since there is no
>   > symbol `||' in Pascal.
> But there's also no #ifdef in Pascal.  If they can learn about #ifdef,
> #define and friends, they can learn about ||. :-)

There is (*$ifdef FOO *), (*$define FOO *), but no `||' in
Pascal.  (In fact GNU Pascal does support `||' because its
preprocessor is a modified `cpp', but I consider C expressions
in a Pascal preprocessor a bug, not a feature, and I am not
planning to encourage their use in Pascal programs.)

>   > There are no header files in Pascal.  One would have to add this
>   > to each source file.
> Err, if you're using cpp, then you have #include capabilities.  How else are
> you testing #ifdefs?

Okay, it seems to be necessary to go a little deeper into the
details.

Pascal has include capabilities - (*$i Foo *) means
#include "foo.pas" - but they are not used for communication
between different modules of the same project.  (Pascal provides
other mechanisms to achieve this.)  Thus, a Pascal project
usually does not have "header" files included by all source
files.

    Peter

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Peter Gerwinski, Essen, Germany, http://home.pages.de/~Peter.Gerwinski/
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