effect of free()

[Rahul Dhesi]

In article <137 at bbxsda.UUCP> scott at bbxsda.UUCP (Scott Amspoker) writes:
>It
>was pointed out that there are no new portability issues that haven't
>been there all along.  In other words, this pointer thing is not new.
>However, nobody has been able to come up with an example where this
>was actually a problem (unless I missed something).  Maybe it is 
>because of the way people write their programs.  Maybe it is because
>C implementers didn't have a standard to hide behind and kept a wide
>safety margin in their products.  

It's probably because portability is not a boolean attribute, and some
things -- like examining a pointer after it has been given to free() --
correspond closely enough to the way most computer systems work that
they are as near being perfectly portable as makes little difference.

The purist point of view seems to be that portability an absolute
attribute, and a C construct either "is" or "isn't" portable.  The
result is the typical "is!" "isn't!" portability war that you often see
here.

In actual practice, the question one really ought to ask is not "is it
portable?" but "how portable is it?"

So how portable is a C program that examines a freed pointer without
dereferencing it?  Probably not 100.000% portable, but close enough
that it makes little difference.

Before worrying about architectures that might not like the type of
thing being discussed, worry about defining too many long macros, or
having long literal strings, or having long external names, or using
#if rather than #ifdef, or doing any type of token-pasting (whether or
not ANSI-conformant), or using data structures that are bigger than 64
kilobytes, or using a word inside a literal string after defining a
macro called by the same name, or continuing a macro definition to the
next line, or any of hundreds of apparently-innocent things that make
C programs less than perfectly portable in the real world.  Then, if
you have any time left, you can relax over lunch and dwell on largely
theoretical endeavors...such as wondering if examining a freed pointer
will give you a C program that might not run on *every* possible
computer system that might exist in the entire world for the next
century.
--
Rahul Dhesi <dhesi%cirrusl at oliveb.ATC.olivetti.com>
UUCP:  oliveb!cirrusl!dhesi