Path: utzoo!mnetor!uunet!husc6!bloom-beacon!mit-eddie!uw-beaver!uw-june!pardo
From: pardo@june.cs.washington.edu (David Keppel)
Newsgroups: comp.lang.c
Subject: Re: C run-time checking
Message-ID: <4465@june.cs.washington.edu>
Date: 15 Mar 88 23:39:23 GMT
References: <763@uvm-gen.UUCP>
Reply-To: pardo@uw-june.UUCP (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 33
Keywords: C arrays pointers run-time-checking

In article <763@uvm-gen.UUCP> hartley@uvm-gen (Stephen J. Hartley) writes:
>
>  I scan this news group every day but don't remember ever seeing a
>discussion about this.  Are there C compilers provided by any
>vendors that generate code to perform run-time checking (toggled
>by an option on the command line, say)?  I have in mind run-time
>checking of the type provided by Pascal compilers, such as checking
>an array subscript against the array bounds, checking a pointer for
>reasonable values before dereferencing it.

I think that this is very difficult to do in C.  Consider a generic
"pointer to char" type that can point into any-ol'-char array.
What's "reasonable"?

There is an alternative, namely to pass the "reasonable" limits to
the pointer when it is assigned, but then this requires the char*
to be structure:

    struct char* {
	val : real char*
	lo : real char*
	hi : real char*
    }

and then what do things like:

    foo = (char *)33;
    foo = NULL;

mean?  We can special case them, but now life has gotten a lot more
complicated.  I won't go into detail, but things do get wierder.

	;-D on  (Dereferencing an idea)  Pardo