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Date: Mon, 21 Sep 2020 23:04:43 +0100
From: Jonathan Wakely <jwakely@...hat.com>
To: Alejandro Colomar <colomar.6.4.3@...il.com>
Cc: Florian Weimer <fweimer@...hat.com>, gcc@....gnu.org,
libstdc++@....gnu.org, Libc-alpha <libc-alpha@...rceware.org>,
libc-coord@...ts.openwall.com
Subject: Re: Expose 'array_length()' macro in <sys/param.h>
On 21/09/20 23:52 +0200, Alejandro Colomar via Libstdc++ wrote:
>I have developed this draft code, the C++ part being based on what you
>wrote.
>
>I am a C programmer, and my C++ is very basic, and I tend to write
>C-compatible code when I need C++, so I can't really write the C++
>part.
>
>I tested the code with all C versions (--std= {c89, c99, c11, c18,
>c2x}), and it worked for all of them (correctly returning 18 in all of
>them), and if I uncomment the part of the pointer, it has a nice error
>message. I used `-Wall -Wextra -Werror -pedantic -Wno-vla
>-Wno-sizeof-pointer-div`.
>
>However, the C++ part needs some work to be able to compile.
>
>Would you mind finishing it?
>
>
>Thanks,
>
>Alex
>------------------------------------------------------------------
>
>#if defined(__cplusplus)
># include <cstddef>
>
># if __cplusplus >= 201703L
># include <array>
That should be <iterator> not <array>.
># define array_length(arr) (std:size(arr))
C++ programmers will not accept a macro for this.
># else
You're missing "template<typename T, std::size_t N>" here.
># if __cplusplus >= 201103L
>constexpr
># endif
>inline std::size_t
>array_length(const T(&array)[N])
Remove the name of the unused parameter.
># if __cplusplus >= 201103L
>noexcept
># endif
>{
> return N;
>}
># endif
>
># if __cplusplus >= 202002L
># define array_slength(arr) (std:ssize(arr))
># else
>
># if __cplusplus >= 201103L
>constexpr
># endif
>inline std::ptrdiff_t
>array_slength(const T(&array)[N])
># if __cplusplus >= 201103L
>noexcept
># endif
>{
> return N;
>}
># endif
>
>
>#else /* !defined(__cplusplus) */
>#include <stddef.h>
>
># define __is_same_type(a, b) \
> __builtin_types_compatible_p(__typeof__(a), __typeof__(b))
># define __is_array(arr) (!__is_same_type((arr), &(arr)[0]))
>
># if __STDC_VERSION__ >= 201112L
># define __must_be(e, msg) ( \
> 0 * (int)sizeof( \
> struct { \
> _Static_assert((e), msg); \
> char ISO_C_forbids_a_struct_with_no_members__; \
> } \
> ) \
>)
># else
># define __must_be(e, msg) ( \
> 0 * (int)sizeof( \
> struct { \
> int : (-!(e)); \
> char ISO_C_forbids_a_struct_with_no_members__; \
> } \
> ) \
>)
># endif
>
># define __must_be_array(arr) __must_be(__is_array(arr), "Must be an
>array!")
>
># define __array_length(arr) (sizeof(arr) / sizeof((arr)[0]))
># define array_length(arr) (__array_length(arr) + __must_be_array(arr))
># define array_slength(arr) ((ptrdiff_t)array_length(arr))
>#endif
>
>
>int main(void)
>{
> int a[5];
> const int x = 6;
> int b[x];
>#if __cplusplus >= 201103L
> constexpr
>#endif
>int y = 7;
> int c[y];
> int *p;
> (void)p;
>
> return array_slength(a) + array_slength(b) +
> array_length(c) /*+
> array_length(p)*/;
>}
>
>
>
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