Subject: 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 <[email-masked]>
Date: Thu, 30 Apr 2015 10:41:30 -0700

Elia Pinto <[email-masked]> writes:

> +#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.