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

Elia Pinto [off-list ref] 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.

On Thu, Apr 30, 2015 at 10:41:30AM -0700, Junio C Hamano wrote:

Elia Pinto [off-list ref] writes:

quoted

+#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

[...]

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.

ISTR that you compile with "-std=c89". typeof was added in c99, I think
(and was a GNU extension before that). I wonder if that is fooling the
gcc version-check.

-Peff