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#include <iostream>using std::cout;using std::endl;struct B { // default access modifier inside struct is public    void set_n(int v) { n = v; }    void f()          { cout << "B::f" << endl; }  protected:    int m, n; // B::m, B::n are protected  private:    int x;}; struct D: B {    using B::m;               // D::m is public    int get_n() { return n; } // B::n is accessible here, but not outside//  int get_x() { return x; } // ERROR, B::x is inaccessible here private:    using B::f;               // D::f is private}; int main() {    D d;//  d.x = 2; // ERROR, private//  d.n = 2; // ERROR, protected    d.m = 2; // protected B::m is accessible as D::m    d.set_n(2); // calls B::set_n(int)    cout << d.get_n() << endl; // output: 2//  d.f();   // ERROR, B::f is inaccessible as D::f    B& b = d; // b references d and "views" it as being type B//  b.x = 3; // ERROR, private//  b.n = 3; // ERROR, protected//  b.m = 3; // ERROR, B::m is protected    b.set_n(3); // calls B::set_n(int)//  cout << b.get_n(); // ERROR, 'struct B' has no member named 'get_n'    b.f();   // calls B::f()    return 0;}