Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!ucsd!ames!killer!vector!rpp386!jfh
From: jfh@rpp386.UUCP (John F. Haugh II)
Newsgroups: comp.lang.c
Subject: Re: data validation (was re self-modifying code)
Summary: interface specifications.
Message-ID: <4661@rpp386.UUCP>
Date: 30 Jul 88 07:34:04 GMT
References: <61251@sun.uucp> <3084@geac.UUCP>
Reply-To: jfh@rpp386.UUCP (The Beach Bum)
Organization: Big "D" Home for Wayward Hackers
Lines: 33

In article <3084@geac.UUCP> daveb@geac.UUCP (David Collier-Brown) writes:
>From article <61251@sun.uucp>, by guy@gorodish.Sun.COM (Guy Harris):
>> input data before using it (unless they have good reason to know the data will
>> *never* be incorrect);
>
>  When I look in my Mutlics standard systems designers' notebook, I
>find the following words of wisdom...
>
>	Subroutines should not check the number or type of input
>  arguments, but assume they have been called correctly.

in my humble opinion, subroutines on the interface boundary SHOULD check
their arguments for conformity to the interface definition.  once inside
of a system of subroutines, there is no need to check for out of band
data.

a well defined interface will specify the action to be taken on each
type of out of band data.  a very well defined interface will specify
EXACTLY how to deal with out of band values.

>  Depending on the hrdware or compiler to catch invalid data by
>trapping on its use has been a known bad practice since well before
>Unix... The manual above is a reprint, circa 1980.

unix has been around longer than since circa 1980.  DEC would seem to
disagree since they included the trap on overflow/etc exceptions to
their double precision machine operands when they created the VAX
family of minicomputers.
-- 
John F. Haugh II                 +--------- Cute Chocolate Quote ---------
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