Path: utzoo!utgpu!watmath!clyde!att!osu-cis!killer!usl!ralph!pja
From: pja@ralph.UUCP (Pete Alleman)
Newsgroups: comp.lang.c
Subject: Re: Run-time Checks for C
Message-ID: <366@ralph.UUCP>
Date: 26 Nov 88 18:05:30 GMT
References: <10113@umn-cs.CS.UMN.EDU>
Reply-To: pja@ralph.UUCP (Pete Alleman)
Organization: Home Sweet Home, Lafayette, LA
Lines: 24

In article <10113@umn-cs.CS.UMN.EDU> raghavan@umn-cs.cs.umn.edu (Vijay Raghavan) writes:
>the C language definition doesn't really preclude any implementation from
>doing certain run-time checks (for array bounds, type checking, referring
>contents of uninitialized pointer variables &c),

The real problem with bounds checking in C is that the implementation is
difficult (if not impossible).  Most high-level languages allow only very
limited pointer arithmetic (array indexing on arrays with known bounds).
Bounds checking in C might be possible is a pointer contained 3 values:
The memory address, an upper bound, and a lower bound.  Pointer arithmetic
would modify only the current value.  Assignment would copy all 3 values.
Can anyone find a flaw in this type of implementation?

>it's just that most
>(okay, all!) implementations don't do any such checking because of efficiency
>reasons. 

I vaguely remember seeing a flyer for a C interpreter that claimed to
check bounds.

-- 
Pete Alleman
	ralph!pja or
	digitran!pja