Macro definition ARRAY_SIZE

Question

I encountered the following macro definition when reading the globals.h in the Google V8 project.

// The expression ARRAY_SIZE(a) is a compile-time constant of t         


        

Answer 1

In the Linux kernel, the macro is defined as (GCC specific):

#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))

where __must_be_array() is

/* &a[0] degrades to a pointer: a different type from an array */
#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))

and __same_type() is

#define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))