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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: memcpy can't take null.
Date: Wed, 08 Apr 2020 13:33:23 -0700
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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
[...]
> If Nemployees is non-zero whilst the pointer employees points to invalid
> memory, it's likely that the bug will be discovered soon enough.
> But if Nemployees is zero and employees is NULL, then the loops through
> the employees array will all be no-ops and have defined, correct
> behaviour. It's only if you call a library function like memcpy that
> the code becomes incorrect.

Your function that takes a pointer to an employee structure and
a count indicating the number of elements in the array should be
accompanied by documentation (at least a comment) that tells the
user what combinations are valid.  If you write a call that violates
those requirements, that call is incorrect -- even if the function
happens not to misbehave.

If that documentation says that func(NULL, 0) is valid and
func(NULL, 1) is not, that's fine -- but then you need to guarantee
that func(NULL, 0) won't blow up in future versions unless you want
to risk breaking existing code.

See memcpy for an example of this.  Ideally, your function should
be documented as clearly.  If it isn't, it might be impossible to
tell whether a given call is correct or not.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */