Alex,
I am all for making things more consistent, but there is also a cost
to changing stuff too much. length is the established
term in most programming languages and I would recommend to stick
to it.
Note that it is not true that the standard consistently refers to
char a[3][n]
as a VLA. It does so in the description in sizeof but not in the
type compatibility rules, at least as understood by most compilers.
This is an inconsistency we *should* fix, but I do not think that
changing away from "length" is a good ida.
Note that "number of elements" is inherently an ambiguous term for
multi-dimensional arrays, and I am not sure how you want to avoid
this without making the wording more complex (e.g. "number of elements
of the outermost array).
So I would recommend not to go this way. You would need a really
good argument to convince me to vote for this, and I haven't seen
any such argument.
Martin
Am Sonntag, dem 01.09.2024 um 11:10 +0200 schrieb Alejandro Colomar:
> Hi Jens, Martin,
>
> On Wed, Aug 14, 2024 at 05:44:57PM GMT, Jens Gustedt wrote:
> > Am 14. August 2024 16:47:32 MESZ schrieb Alejandro Colomar
> > <a...@kernel.org>:
> > > > > I was thinking of renaming the proposal to elementsof(), to avoid
> > > > > confusion between length of an array and length of a string. Would
> > > > > you
> > > > > mind checking if elementsof() is ok?
> > > >
> > > > No, not for me. I really want as to go consistently to talk about
> > > > array length for this. Consistent terminology is important.
> > >
> > > I understand your desire for consistency. I think your paper is a net
> > > improvement over the status quo (which is a mix of length, size, and
> > > number of elements). After your proposal, there will be only length and
> > > number of elements. That's great.
> > >
> > > However, strlen(3) came first, and we must respect it.
> >
> > Sure, string length, a dynamic feature, and array length are two features.
> >
> > But we also have VLA and not VNEA in the standard, So we should respect
> > this ;-)
>
> I hadn't thought about it until yesterday after Martin insisted in
> preferring lengthof over nelementsof or a contraction of it, and worried
> about nelementsof possibly causing ambiguity with multi-dimensional
> arrays. But:
>
> VLA is a misnomer.
> ~~~~~~~~~~~~~~~~~~
>
> First, let's assume length refers to the number of elements, as we all
> agree that length should not refer to the size in bytes of an array,
> since we already have the term "size" for it, which is consistent with
> sizeof.
>
> int vla[3][n];
>
> The array from above is a so-called variable length array, according to
> the standard. But it does not have a variable length, according to the
> presumed meaning of length. It does indeed have a variable size. The
> element of vla is itself an array, which is the one that really has a
> variable length (or number of elements, as is the more technical term).
>
> So, if n3187 develops, and really pretends to uniquely and unambiguously
> use a term for the number of elements and another one for the size of an
> array, it should also rename "variable length array" into "variable size
> array".
>
> It is indeed due to this problematic misuse of the colloquial term
> length that "lenght" and not "number of elements" is misleading in
> multi-dimensional arrays. The standard is very strict in using NoE for
> the first dimension of an array (so its true dimension), and not for
> the dimensions of arrays that are elements of it.
>
> And now you could say that this is only a problem of multi-dimensional
> arrays. It's not. They're just the composition of arrays with elements
> of type array. The same problem arises with single dimensional arrays
> in complex situations (although, admittedly, this is non-standard):
>
> $ cat vla.c
> int
> main(void)
> {
> int n = 5;
>
> struct s {
> int v[n];
> };
>
> struct s a[3];
>
> return sizeof(a);
> }
> $ gcc -Wall -Wextra -Wpedantic vla.c
> vla.c: In function ‘main’:
> vla.c:7:22: warning: a member of a structure or union cannot have a
> variably modified type [-Wpedantic]
> 7 | int v[n];
> | ^
> $ ./a.out; echo $?
> 60
>
> a is a VLA even if it is a single-dimension array of known constant
> number of elements. Huh? :)
>
> Terminology
> ~~~~~~~~~~~
>
> Once we've determined that "length" in VLA does refer to the size and
> not the number of elements, it's hard to justify a reformation of
> terminology that would base on length meaning number of elements.
>
> Indeed, either basing justifications of the origins of length on
> strlen(3) or on VLA, we must conclude that "variable length array" must
> be renamed to "variable size array". I'm preparing a paper for that.
>
> If eventually that paper would be accepted, I'd prepare a second paper
> that would reform every use of size and length with arrays so that size
> always refers to the size in bytes, length is completely removed, and
> number of elements stands as the only term to refer to the number of
> elements.
>
>
> Have a lovely day!
> Alex
>
> > > Since you haven't proposed eliminating "number of elements" from the
> > > standard, and it would still be used alongside length, I think
> > > elementsof() would be consistent with your view (consistent with "number
> > > of elements").
> >
> > didn't we ? Then this is actually a good idea to do so, thanks for the idea
> > !
>
