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Date: Mon, 21 Sep 2020 23:52:13 +0200
From: Alejandro Colomar <colomar.6.4.3@...il.com>
To: Jonathan Wakely <jwakely@...hat.com>, Florian Weimer <fweimer@...hat.com>
Cc: 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>
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>
# define array_length(arr) (std:size(arr))
# else
# if __cplusplus >= 201103L
constexpr
# endif
inline std::size_t
array_length(const T(&array)[N])
# 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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