Path: utzoo!attcan!uunet!mcvax!hp4nl!eutrc3!eutwc1!wzv!wietse
From: wietse@wzv.UUCP (Wietse Venema)
Newsgroups: comp.lang.c
Subject: Re: How do a write portable programs?
Summary: remember VOS
Keywords: portable OS interface
Message-ID: <141@wzv.UUCP>
Date: 8 Sep 88 21:54:05 GMT
References: <1056@nmtsun.nmt.edu>
Reply-To: wietse@wzv.UUCP (Wietse Venema)
Organization: Home (Eindhoven, NL)
Lines: 29

In article <1056@nmtsun.nmt.edu> warner@hydrovax.nmt.edu (M. Warner Losh) writes:
>How do I write program that are easily protable when I HAVE TO use the
>system calls (be they setitimer() or lib$init_timer() or int21()...).  Is
>there a good and easy way that I can write my programs so that most of the
>code never has to be touched when I port?  What is the best way of handling
>system dependent routines?  Assume the whole world is UNIX and then write
>UNIX system call emulation on those that aren't?  Or should I write
>routines that will do some functions (say turn off echo, but that is a bad
>example) regardless of how that function gets done.  Should I use zillions
>of #ifdefs everywhere? or should there be files that contain source code
>for only one system? 

You might take a look at `software tools' by Kernighan and Plauger.
It's a little old (1978) and uses a different language (Ratfor), but
provides good examples of encapsulating system-dependent code in a small
collection of interface routines.  I must admit that this portable
interface is patterned after the standard UNIX programming interface.

These ideas have been elaborated by some people (at Berkeley?) and
resulted in VOS, a virtual operating system. Basically, it is a thin
layer of routines that map requests to system calls of the local OS.
Porting software then becomes a matter of writing an appropriate VOS
implementation.

			Wietse
-- 
work:	wswietse@eutrc3.uucp	| Eindhoven University of Technology
ditto:	wswietse@heitue5.bitnet	| Mathematics and Computing Science
home:	wietse@wzv.uucp		| 5600 MB Eindhoven, The Netherlands