Hi Jens, Martin, On Wed, Aug 14, 2024 at 08:11:20AM GMT, Jens Gustedt wrote: > > Checking <https://codesearch.debian.net>, I see that while several > > projects have a lengthof() macro, all of them use it with semantics > > compatible with this keyword, so it shouldn't break too much. Maybe > > those projects will start receiving diagnostics that they're redefining > > a standard keyword, but that's not too bad. > > For a WG14 paper you should add these findings to support that choice. > Another option would be for WG14 to standardize the then existing > implementation with the double underscores.
Makes sense; I'll add that into new "Prior art" and "Backwards compatibility" sections within the paper. > > > As for the parentheses, I personally think lengthof should follow > > > similar rules compared to sizeof. > > > > I think most people agree with this. > > I still don't, in particular not for standardisation. > > We have to remember that there are many small C compilers out there. > I would not want unnecessary burden on them. So my preferred choice would be > a standardisation as a macro, similar to offsetof. > gcc (and clang) could then just map that to their builtin, other compilers > could use > whatever they have at the moment, even just the macros that you have in the > paper as a starting point. > > The rest would be "quality of implementation" Hmmm, sounds reasonable. Some doubts: If we allow a compiler to implement it as a predefined macro that expands to the usual sizeof division, it might produce double evaluation in some VLA cases. That would be surprising to some programs, which may expect either 0 or 1 evaluations, but not 2. Maybe we can leave it as unspecified behavior, and an implementation may document that double evaluation may happen if the input is a VLA? > What time horizon do you see to add the feature for array parameters? Martin, what do you think? I think the only blocking thing for me is what you mentioned about turning function parameters into arrays that decay almost everywhere. Once that's set up, my code will probably work with them without modification, or maybe with just a little tweak. Do you have an idea of how much time that can take you? I expect it to be well before C2y. Maybe a year or two? Have a lovely day! Alex > Thanks > Jens -- <https://www.alejandro-colomar.es/>
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