www.gusucode.com > C++ Primer 书籍源代码源码程序 > C++ Primer 书籍源代码源码程序/code/13/old/smart-ptr.cpp
//Download by http://www.NewXing.com #include <iostream> using std::ostream; using std::cout; using std::endl; #include <string> #include <cstddef> using std::size_t; //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() { delete ip; } }; class HasPtr { public: // HasPtr owns the pointer; p must have been dynamically allocated HasPtr(int *p, int i): ptr(new U_Ptr(p)), val(i) { } // copy members and increment the use count HasPtr(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) delete ptr; } friend ostream& operator<<(ostream&, const HasPtr&); // copy control and constructors as before // accessors must change to fetch value from U_Ptr object int *get_ptr() const { return ptr->ip; } int get_int() const { return val; } // change the appropriate data member void 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 class int val; }; HasPtr& HasPtr::operator=(const HasPtr &rhs) { ++rhs.ptr->use; // increment use count on rhs first if (--ptr->use == 0) delete ptr; // if use count goes to 0 on this object, delete it ptr = rhs.ptr; // copy the U_Ptr object val = rhs.val; // copy the int member return *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 = 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 point ptr2.get_ptr_val(); // returns 42 cout << "(2) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl; ptr1.set_int(0); // changes s member only in ptr1 ptr2.get_int(); // returns 42 ptr1.get_int(); // returns 0 cout << "(3) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl; } void f3() { int obj; HasPtr p1(&obj, 42); HasPtr p2(p1); // p1 and p2 both point to same int object HasPtr p3(p1); // p1, p2, and p3 all point to same int object }