#include <iostream>
using std::ostream; using std::cout; using std::endl;
#include <string>
#include <cstddef>
using std::size_t;
/* smart pointer class: takes ownership of the dynamically allocated*                      object to which it is bound * User code must dynamically allocate an object to initialize a HasPtr* and must not delete that object; the HasPtr class will delete it
*/
//private class for use by HasPtr only
class U_Ptr {friend class HasPtr;int *ip;size_t use;U_Ptr(int *p): ip(p), use(1) { }~U_Ptr() { cout << "U_Ptr destructor" << endl; delete ip; }
};class HasPtr {
public:// HasPtr owns the pointer; p must have been dynamically allocatedHasPtr(int *p, int i): ptr(new U_Ptr(p)), val(i) { }// copy members and increment the use countHasPtr(const HasPtr &orig):ptr(orig.ptr), val(orig.val) { ++ptr->use; }HasPtr& operator=(const HasPtr&);// if use count goes to zero, delete the U_Ptr object~HasPtr() { if (--ptr->use == 0) {cout << "HasPtr destructor" << endl;delete ptr; }} friend ostream& operator<<(ostream&, const HasPtr&);// copy control and constructors as before// accessors must change to fetch value from U_Ptr objectint *get_ptr() const { return ptr->ip; } int get_int() const { return val; }// change the appropriate data membervoid set_ptr(int *p) { ptr->ip = p; }void set_int(int i) { val = i; }// return or change the value pointed to, so ok for const objects// Note: *ptr->ip is equivalent to *(ptr->ip)int get_ptr_val() const { return *ptr->ip; } void set_ptr_val(int i) { *ptr->ip = i; }
private:U_Ptr *ptr;        // points to use-counted U_Ptr classint val;
};HasPtr& HasPtr::operator=(const HasPtr &rhs)
{++rhs.ptr->use;     // increment use count on rhs firstif (--ptr->use == 0) {cout << "operator= delete" << endl;delete ptr;    // if use count goes to 0 on this object, delete it
    }ptr = rhs.ptr;      // copy the U_Ptr objectval = rhs.val;      // copy the int memberreturn *this;
}ostream& operator<<(ostream &os, const HasPtr &hp)
{os << "*ptr: " << hp.get_ptr_val() << "\tval: " << hp.get_int() << endl;return os;
}int main()
{int *obj = new int(0);HasPtr ptr1(obj, 42);HasPtr ptr2(ptr1);cout << "(1) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl;ptr1.set_ptr_val(42); // sets object to which both ptr1 and ptr2 pointptr2.get_ptr_val();   // returns 42
cout << "(2) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl;ptr1.set_int(0);   // changes s member only in ptr1ptr2.get_int();    // returns 42ptr1.get_int();    // returns 0
cout << "(3) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl;
}