Path: utzoo!attcan!uunet!mcvax!hp4nl!ruuinf!piet
From: piet@ruuinf (Piet van Oostrum)
Newsgroups: comp.lang.modula2
Subject: Re: C++ vs. Modula2
Message-ID: <981@ruuinf.UUCP>
Date: 16 Jan 89 08:54:26 GMT
References: <INFO-M2%89011219330825@UCF1VM>
Sender: piet@ruuinf.UUCP
Reply-To: piet@ruuinf (Piet van Oostrum)
Organization: Dept of Computer Science, University of Utrecht, Holland
Lines: 38
In-reply-to: alk@UX.ACSS.UMN.EDU

In article <INFO-M2%89011219330825@UCF1VM>, alk@UX writes:
`As was recently observed in the info-pascal mailing list, optimization ->
`conditional compilation.  Consider:
`      .
`      :
`      CONST
`      .
`      :
`        OpSys = VMS;
`      .
`      :
`      IF OpSys = VMS THEN
`        DoVMSStuff
`      ELSE
`        DoOtherOSStuff;
`      .
`      :
`
`All but the most inanely STUPID of compilers will completely eliminate the
`unreachable code.

This only helps for statements, not for declarations.

`
`>Allocation of space for records (particularily alignment) is unclear in Modula.
`>Operating system calls frequently return pointers to records with some
`>operating system defined layout. Mapping these on Modula records is, due to
`>alignment, compiler dependent.

This is also true for C. I had a problem recently on our HCX/UX system
where the compiler insists on aligning a lot, and where this gave problems
in one of the COFF format structs, that have a long word not aligned on a
four-byte boundary. I could get along with hacking a short in front of it
and reading/writing the second to last fields.
-- 
Piet van Oostrum, Dept of Computer Science, University of Utrecht
Padualaan 14, P.O. Box 80.089, 3508 TB Utrecht, The Netherlands
Telephone: +31-30-531806. piet@cs.ruu.nl (mcvax!hp4nl!ruuinf!piet)