Segmentation fault while reading Memory in C++ - c++

Question

I am just trying to get Value stored at a specific memory address using two C++ codes
Code which I using to write data to memory and get its address :
#include <iostream>
using namespace std;
int main()
{
int i = 10;
cout<<&i<<endl;
cin>>i; // This is just to make sure program doesn`t end
return 0;
}
I used cin>>i; just to make sure that it doesn't end.
After getting the address of int i, put in the following code :
#include <iostream>
using namespace std;
int main()
{
// This address changes everytime and I change it everytime
// This is just one temporary address
volatile int *x = (volatile int *)0x7ffef9246e74; // [1]
int y = *x;
cout<<y<<endl;
return 0;
}
[1] : I copied this line from this page.
Program #1 keeps running while I run Program #2
On running the second code, I am getting segmentation fault (core dumped). Any help?

Answer 1

Your model of how modern operating systems, compilers, etc. work is wrong. When you run the program the first time, the process gets assigned a memory space. Everything within this memory space, which is a virtual memory space, gets mapped to physical memory by the processor's MMU.
When the process finished, its memory space no longer exists. The next time you start the same program, it will run in another and independent memory space. It might be mapped to different physical memory addresses and even the virtual addresses are either not the same or they are cleared to make sure that no information is leaked from former processes.
This means that when you enter the address from the first program into the second, it has no meaning there. What is worse is that the memory address from the first run is not part of the virtual memory space of the second one when you run it, hence the CPU's MMU detects an illegal access to a memory location and you get a seg-fault.