effect of free()

[Ian Dall]

In article <14343 at haddock.ima.isc.com> karl at haddock.ima.isc.com (Karl Heuer) writes:
>In article <568 at augean.OZ> Ian Dall writes:
>>In article <1989Aug17.005548.745 at twwells.com> bill at twwells.com (T. William Wells) writes:
>>>	free(ptr);
>>>	if (ptr == 0) ...
>>>The if might cause a trap when the value of ptr is accessed.
>The issue is not whether the value of ptr has changed.  Some architectures
>distinguish between arithmetic registers and address registers, and refuse to
>allow arbitrary garbage to be loaded into an address register.

"free" or ANY function cannot change it's argument. "free" should not load
anything into "the special address register" (let alone "arbitrary garbage").

>>The compiler doesn't know what malloc and free do. For all the
>>compiler knows malloc and free could be functions you wrote with
>>completely different semantics.
>
>That's implementation-dependent.  For all you know, malloc() and free() are
>builtins on my compiler.

Your compiler can define any builtins it likes, but if they don't work like
real functions they haven't been done properly.

I don't have a copy of the ANSI standard, but surely any specification of the
behaviour of standard fuctions is to be read in conjunction with the defined
behaviour of ANY function. Which is call by value.


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-- 
 Ian Dall           life (n). A sexually transmitted disease which afflicts
                              some people more severely than others.
idall at augean.oz