C Pointer Arithmetic sizeof(struct)

Question

Here is the code in question

#include 

struct test {
    unsigned char t;
    unsigned short u;
    unsigned char v;
};


int main ()
{
    s         


        

Answer 1

The problem is that when you do pointer arithmetic, it increments by a multiple of the size of the datatype.

So what you're effectively doing is adding by the square of sizeof(struct test).

Since sizeof(struct test) = 6, you are incrementing the address by 6 * 6 = 36. Hence why you get 0x1024 and 0xfdc instead of 0x1006 and 0xffa. (You also switched the + and -, but that's a small thing.)

Instead, just do this:

printf("%x %p %p\n",
       sizeof(struct test),
       a + 1,
       a - 1);