How data secured from out side world in c plus plus?

Answer 1

In C++, data is not secured from the outside world it is merely protected from accidental mutation. A determined programmer can easily circumvent the encapsulation of an object. Consider the following:

class X {

int data; // private by default

};

Here, the data member is declared private (the default access for a class), however the class definition exposes the implementation details making it possible to define the exact same class with public access under a different name:

struct Y {

int data;

};

Given that X and Y both have the same memory layout, it is trivial to undermine the encapsulation of an X by casting to a Y:

void f (X& x) {

x.data = 42; // error: x.data is private

Y& y {(Y&) x}; // refer to x as if it were really a Y with pubic access

y.data = 42; // ok

}