C++ Pointers: Address - Address Confusion

Asked Jun 17 '20 at 15:22

Active Jun 17 '20 at 15:22

Viewed 37 times

I am trying to understand pointer arithmetic in C++ but I just don't get it why the below code gives a weird output which I cannot comprehend.

using namespace std;

int main() {
int *p1, *p2;
int x = 100;
int y = 200;
p1 = new int;
p2 = new int;

*p1 = 100;
*p2 = 200;

    cout<<p1<<endl;
    cout<<p2<<endl;

    cout<<p2 - p1<<endl;

    return 0;
}

This gives an output as follows:

0x7fffd46d2e70

0x7fffd46d2e90

8

I do not understand how come p2 - p1 is 8. Which I believe is the size of the pointer. But shouldn't it be 20?? (as calculated below)

0x7fffd46d2e90 - 0x7fffd46d2e70 = 20

or 20 / 2 = 10??

Hope I can get this cleared and some more explanation on pointer arithmetic. Specifically when we subtract an address from another address

asked Jun 17 '20 at 15:22

pratt33k

An int has sizeof(4), 0x20 / 4 is 8. – tkausl Jun 17 '20 at 15:25
Firstly, you need to learn the difference between decimal and hexadecimal. Secondly... – underscore_d Jun 17 '20 at 15:25
2

duplicate of [Pointer subtraction confusion](https://stackoverflow.com/questions/3238482/pointer-subtraction-confusion) – underscore_d Jun 17 '20 at 15:25
2

Shockingly bad duplicate. Different language for starters. Plus this one is about the difference between two pointers that are not in the same array. The behaviour of the code in this question is undefined. – Bathsheba Jun 17 '20 at 15:32
This code was in the Algorithms and Data structures notes – pratt33k Jun 17 '20 at 15:34

C++ Pointers: Address - Address Confusion

0 Answers0