How do a write portable programs?

[Wietse Venema]

In article <1056 at nmtsun.nmt.edu> warner at 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
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