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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.lang.ada,comp.lang.c,sci.space,sci.space.shuttle
Subject: Re: "C" vrs ADA
Message-ID: <8513@utzoo.UUCP>
Date: Sat, 29-Aug-87 02:25:25 EDT
Article-I.D.: utzoo.8513
Posted: Sat Aug 29 02:25:25 1987
Date-Received: Sat, 29-Aug-87 02:25:25 EDT
References: <1065@vu-vlsi.UUCP> <2231@cbmvax.UUCP> <36@sarin.UUCP>
Organization: U of Toronto Zoology
List-Id: <comp.lang.ada>

> Um...  How do these [safe] C environments detect subscript range errors
> in a piece of code like:
> 
>         strcpy(s,t)
>         char *s, *t;
>         { while (*s++ = *t++); return s;}

Easy, a pointer becomes a non-trivial data structure that carries bounds
with it; those bounds are checked when it is used.  Remember that pointer
arithmetic is technically legal only within a single array.  Getting the
little details right must be a bit tricky in spots, but it does work.

> Although an unhandled exception in C "typically" produces a dump,
> it does not "always" produce a dump.  Also, the dump may occur long
> after the invalid code was executed, making it more difficult to figure
> out what went wrong.

This property is shared by *all* programming languages that can generate
run-time exceptions; usually the actual exception shows up at some remove
from the bug that actually caused it.  Unless Ada is much more radical
than I remember (it's been a long time since I read the definition),
it is just as subject to this problem as C.
-- 
"There's a lot more to do in space   |  Henry Spencer @ U of Toronto Zoology
than sending people to Mars." --Bova | {allegra,ihnp4,decvax,utai}!utzoo!henry