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From: sjs@gnv.ifas.ufl.edu
Newsgroups: comp.lang.c
Subject: Re: Portability Issues
Message-ID: <1991Apr24.115543.123@gnv.ifas.ufl.edu>
Date: 24 Apr 91 16:55:43 GMT
References: <2573@plx.UUCP>
Lines: 50

In article <2573@plx.UUCP>, ming@plxsun.uucp (Lak-Ming Lam) writes:
> I would like to develop program which can be portable to different system
> (e.g. PC/MS-DOS, UNIX, Mac OS, etc.).  I would like to have anyone of you
> help me on the following issues:
> 
> ...
> o	how to use one set of source code to support different systems
> 	(using #if MSDOS etc. or some other ways)
> ...

I write in C for the PC and a VAX.  I have a special include files whose
contents are different on the PC and VAX, so I don't have to change the
specifications in the source code.  Example:

#include "setups.h"

where the contents on the PC would be for PC-specific setups, and the
contents on the VAX would be for VAX-specific setups.

At places where I have to use a machine-specific function (like keyboard
handlers), I make a common name that I use throughout my code, and supply
the machine-specific reference on the appropriate computer.  For example:

	get_key_press (&key_value);

The setups.h file on the PC may use a #define or a full function to
take care of the keypress routine on the PC; the setups.h file on the
VAX would define or use VAX-specific functions.  I'd use #defines to
assign words like EXIT or CANCEL to represent the key functions instead
of passing back actual key values; this will make it easier to set
things up in a switch block.

The object is to create a maximum core of code that will work unchanged
on more than one computer; supply computer-specific code in separate
.h or .c files, which each residing on its respective machine.

While this may result in some nested function calls to finally
get to a computer-specific function, it will be much easier to
manage.  Unless speed is very critical, given the number of machines
you are going to write your code for, I'd trade a few clock ticks
for maximum common code.


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