Re: [PATCH v3] git-compat-util.h: implement a different ARRAY_SIZE macro for for safely deriving the size of array

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 30, 2015, 17:41 UTC
Message-ID: <xmqqd22l1pkl.fsf@gitster.dls.corp.google.com>
In-Reply-To: <1430397854-28908-1-git-send-email-gitter.spiros@gmail.com>

Elia Pinto <gitter.spiros@gmail.com> writes:

Show 23 quoted lines

> +#if defined(__GNUC__) && (__GNUC__ >= 3)
> +# if GIT_GNUC_PREREQ(3, 1)
> + /* &arr[0] degrades to a pointer: a different type from an array */
> +# define BARF_IF_IS_NOT_AN_ARRAY(arr)						\
> +	BUILD_ASSERT_OR_ZERO(!__builtin_types_compatible_p(typeof(arr), \
> +							typeof(&(arr)[0])))
> +# else
> +#  define BARF_IF_IS_NOT_AN_ARRAY(arr) 0 
> +# endif
> +#endif 
> +/*
> + * ARRAY_SIZE - get the number of elements in a visible array
> + *  <at> x: the array whose size you want.
> + *
> + * This does not work on pointers, or arrays declared as [], or
> + * function parameters.  With correct compiler support, such usage
> + * will cause a build error (see the build_assert_or_zero macro).
> + */
> +#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + BARF_IF_IS_NOT_AN_ARRAY(x))
> +
>  #define bitsizeof(x)  (CHAR_BIT * sizeof(x))
>  
>  #define maximum_signed_value_of_type(a) \

Hmmmmmmmm.

    CC ws.o
ws.c: In function 'parse_whitespace_rule':
ws.c:46:3: error: unknown type name 'typeof'
   for (i = 0; i < ARRAY_SIZE(whitespace_rule_names); i++) {
   ^

$ gcc --version gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2 Copyright (C) 2013 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.