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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: UB of memcpy(NULL, NULL, 0)
Date: Sat, 22 Oct 2016 16:33:23 -0700
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Lőrinczy Zsigmond <nospam@for.me> writes:
> That might be very true, but not really relevant
> when talking about the standard describing
> function 'memcpy'

What might be very true?  Please quote some context from the article
you're replying to.

> IMHO it could mention that reading from unreadable address,
> or writing into unwriteable address is UB,
> but that is true for every function dealing with pointers.
>
> I think, important points would be these:
>
> * if len==0, memcpy should do nothing

That would have been a reasonable definition, but it's not what the
standard says.  Your opinion that it *should* do nothing in that
case is a perfectly valid one, but it's not one that everyone shares.

Personally, I have no particular problem with memcpy(NULL, NULL, 0)
having undefined behavior.  I've never written non-contrived code that
would be affected by it, and if I needed to I'd simply add an if
statement and move on.

> * if the from-area and to-area overlap, it is UB

Already specified.

> * if from+len<from or to+len<to (address wrap-around), it is UB

Already specified, though not in those terms.  The standard says nothing
about address arithmetic wrapping around; it simply makes certain
operations undefined behavior.

-- 
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"