Confused about pointer adding/subtracting

[LB]

I am very confused.                                                              Output:

1 2 3 4 5

int a[2]; a[0] = 3; a[1] = 7; int *p = a; cout << *p + *(p+sizeof(int)) << endl;

10

I compiled and ran this on two separate computers. My assumption is that adding X to pointers makes it point to a value X bytes later. (I have never had to deal with adding to/subtracting from pointers that point to types larger than one byte, so I could be completely off on this assumption) However, I get a strange error with this:

void *vp = new int[2];
vp + 4; //error C2036: 'void *' : unknown size
delete[] vp;

Surely it should understand that a void pointer can be incremented by X bytes?

[o1vk4iN6]

It's just as the error says, void doesn't have a size.

int a[5];

cout << a[4] << endl;
//equivalent
cout << *(a + 4) << endl;

essentially when you add "4", you are actually adding "4 * sizeof(int)" to the pointer. Since void isn't a type it doesn't know what size to increment by.

If you want to increment by bytes than typecast to "char*".

EDIT: just so it doesn't confuse you, int a[5] is techniquelly a pointer, just it allocates local memory (stack) and places the pointer to that memory in it for you.

[LB]

Oh, huh - I guess I got really lucky on both computers >_<

Thanks!