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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: UB of memcpy(NULL, NULL, 0)
Date: Sun, 23 Oct 2016 14:15:00 -0700
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Malcolm McLean <malcolm.mclean5@btinternet.com> writes:
> On Sunday, October 23, 2016 at 8:21:43 PM UTC+1, Keith Thompson wrote:
>> Meanwhile, any remaining problems can be avoided simply by *not*
>> passing null pointers to memcpy().  The effort needed to do this is
>> nonexistent in most cases, and minimal in all other cases.
>> 
>>
> /*
>   It is possible for a company to have zero employees, but it's
>   highly unusual.
> */
> void foo(Employee *e, int Nemployees)
> {
>   Employee *s = malloc(N * sizeof(Employee));
>   
>   memcpy(s, e, N * sizeof(Employee));
> }
>
> That's the snag. This bug will lurk and could pop up at any
> inconvenient moment for reasons which are hard to understand,
> eg the malloc() implementation changes.

Yes, the behavior of malloc(0) is implementation-defined.  You need to
be aware of that and allow for it.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"