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SubjectRe: Expose 'array_length()' macro in <sys/param.h>
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Date
Thanks again for your improvements.

I think this might be ready for a patch already.
Any more thoughts?

Thanks,

Alex

------------------------


#if defined(__cplusplus)
# include <cstddef>

# if __cplusplus >= 201103L
template<typename _Tp, std::size_t _Len>
constexpr inline std::size_t
__array_length(const _Tp(&)[_Len]) __THROW
{
return _Len;
}

template<typename _Tp, std::size_t _Len>
constexpr inline std::ptrdiff_t
__array_slength(const _Tp(&)[_Len]) __THROW
{
return _Len;
}
# else /* __cplusplus < 201103L */
template<typename _Tp, std::size_t _Len>
char (&__array_length(const _Tp(&)[_Len]))[_Len];
# define __array_length(_Arr) (sizeof(__array_length(_Arr)))
# define __array_slength(_Arr) \
(static_cast<std::ptrdiff_t>(__array_length(_Arr)))
# endif /* __cplusplus >= 201103L */


#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(_Expr, _Msg) ( \
0 * (int)sizeof( \
struct { \
_Static_assert((_Expr), _Msg); \
char _ISO_C_forbids_a_struct_with_no_members; \
} \
) \
)
# else
# define __must_be(_Expr, _Msg) ( \
0 * (int)sizeof( \
struct { \
int : (-!(_Expr)); \
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_len(_Arr) (sizeof(_Arr) / sizeof((_Arr)[0]))
# define __array_length(_Arr) (__array_len(_Arr) + __must_be_array(_Arr))
# define __array_slength(_Arr) ((ptrdiff_t)__array_length(_Arr))
#endif /* defined(__cplusplus) */


static int a[5];
static int v[__array_slength(a)];
static int w[__array_length(v)];
static int *p;

int main(void)
{
int aa[5];
const int xx = 6;
int vv[xx];
int yy = 7;
int ww[yy];
int *pp;

(void)p;
(void)pp;
(void)ww;

return __array_slength(a)
+ __array_length(v)
+ __array_slength(w)
/* + __array_length(p) */ /* Always breaks :) */
+ __array_length(aa)
+ __array_slength(vv)
+ __array_length(ww) /* Not in C++ */
/* + __array_length(pp) */ /* Always breaks :) */
;
}

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