Regarding shallow copy

[Jeff0803]

Here is a sample program.

#include <iostream>
using namespace std;
struct S {
int *p;
};

S x{ new int{0} };
void f()
{
S y{ x }; // "copy" x

*y.p = 1; // change y; affects x
*x.p = 2; // change x; affects y
delete y.p; // affects x and y
y.p = new int{ 3 }; // OK:change y;does not affect x
*x.p = 4; // ?
}
int main()
{
f();
return(0);
}

I expected an error occur at *x.p = 4 because x is copied to y, y.p is deleted and then new memory is allocated to it, and *x.p = 4 is trying to write to deallocated memory.

However there's no crash and *x.p and *y.p are both 4.

Can anybody explain this?

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