c++ program:unexpected output

[venkatacplpl]

#include<iostream>
using namespace std;



struct elem{
int a;
int b;
};

void display(elem *ptr);



int main()
{
elem *ptr=new elem();
display(ptr);
return 0;

}


void display(elem *ptr1)
{  ptr1->a=5;
   ptr1->b=6;
elem*ptr2=ptr1++;
cout<<ptr1<<endl<<ptr2<<endl;
cout<<ptr2->a<<endl<<ptr2->b<<endl;
}

This simple program is giving unexpected output:

0x84ba010
0x84ba008
5
6

1.Why is it displaying 5 and 6 which are contents of ptr1 ,when I actually displayed contents of ptr2 which should have resulted in segmentation fault.

2.when it didnt lead to segmentation fault I displayed ptr1 and ptr2 and difference between those two pointers is just 2 bytes(0x84ba010-0x84ba008=2) which should be 4 bytes as elem struct has 2 integers.

please help!!

[jlb]

Do you realize that you have computed the difference of the pointers incorrectly? Remember the values are in hexadecimal not decimal (0x10 == 16).

And as far as your first question, welcome to the world of undefined behavior where anything can happen.