6.23 Arithmetic on void- and Function-Pointers

In GNU C, addition and subtraction operations are supported on pointers to void and on pointers to functions. This is done by treating the size of a void or of a function as 1.

A consequence of this is that sizeof is also allowed on void and on function types, and returns 1.

The option -Wpointer-arith requests a warning if these extensions are used.

typedef int boot_os_fn (int flag, int argc);
sizeof(boot_os_fn) 大小為 1
sizeof(void) 大小為 1


基本疑惑在函式型別上
typedef int(*boot_os_fn) (int flag, int argc);
sizeof(boot_os_fn) 大小為 4 或者8  32bit or 64bit 系統上