Hi
Am 7. August 2024 17:05:48 MESZ schrieb Joseph Myers <josmy...@redhat.com>:
> On Wed, 7 Aug 2024, Alejandro Colomar wrote:
>
> > +@node Length
> > +@section Determining the Length of Arrays
> > +@cindex lengthof
> > +@cindex length
> > +@cindex array length
> > +
> > +The keyword @code{__lengthof__} determines the length of an array operand,
> > +that is, the number of elements in the array.
> > +Its syntax is just like @code{sizeof}.
> > +The operand must be a complete array type.
>
> I think you mean the operand must be *an expression whose type is a
> complete array type* or *a type name for a complete array type*. The
> wording you have suggests only type names, you need to be clear about both
> kinds of operands being possible (and include examples for them).
>
> > +@smallexample
> > +__lengthof__ (int [7][n++]); // constexpr
> > +__lengthof__ (int [n++][7]); // run-time value
> > +@end smallexample
>
> I don't think using "constexpr" to mean "constant expression" is a good
> idea, they're different things.
It should actually state "integer constant expression", I think. the nuance is
probably important
> > +void
> > +incomplete (int p[])
> > +{
> > + unsigned n;
> > +
> > + n = __lengthof__ (x); /* { dg-error "incomplete" } */
> > +
> > + /* We want to support the following one in the future,
> > + but for now it should fail. */
> > + n = __lengthof__ (p); /* { dg-error "invalid" } */
>
> This seems to be the only test you have for a non-array operand. I'd
> expect such tests (both for type name operands and for expression
> operands) covering cases that we *don't* want to support in future, not
> just this one that we would like to be supportable in future.
>
> I don't see any tests for the constraints on external definitions from
> 6.9.1 that we discussed - that referenced to undefined internal linkage
> identifiers are OK inside __lengthof__ returning a constant (both
> constant-length arrays of non-VLA and constant-length arrays of VLA) but
> not in the cases where __lengthof__ is evaluated.
>
--
Jens Gustedt - INRIA & ICube, Strasbourg, France
