Re: Expose 'array_length()' macro in <sys/param.h>

[Jonathan Wakely <jwakely@redhat.com>]

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)*/;
>}
>
>
>