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/value-ptr.cpp
//Download by http://www.NewXing.com #include <iostream> using std::ostream; using std::cout; using std::endl; #include <string> class HasPtr { public: // no point to passing a pointer if we're going to copy it anyway // store pointer to a copy of the object we're given HasPtr(const int &p, int i): ptr(new int(p)), val(i) {} // copy members and increment the use count HasPtr(const HasPtr &orig): ptr(new int (*orig.ptr)), val(orig.val) { } HasPtr& operator=(const HasPtr&); // wrong: don't define a destructor without also defining copy and assign ~HasPtr() { delete ptr; } friend ostream& operator<<(ostream&, const HasPtr&); // accessors must change to fetch value from Ptr object int get_ptr_val() const { return *ptr; } int get_int() const { return val; } // change the appropriate data member void set_ptr(int *p) { ptr = p; } void set_int(int i) { val = i; } // return or change the value pointed to, so ok for const objects int *get_ptr() const { return ptr; } void set_ptr_val(int p) const { *ptr = p; } private: int *ptr; // points to an int int val; }; HasPtr& HasPtr::operator=(const HasPtr &rhs) { // Note: Every HasPtr is guaranteed to point at an actual int; // We know that ptr cannot be a zero pointer *ptr = *rhs.ptr; // copy the value pointed to val = rhs.val; // copy the int 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); // int* member points copy of obj, val is 42 HasPtr ptr2(ptr1); // int* member points new copy obj, val is 42 cout << "(1) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl; ptr1.set_ptr_val(42); // sets copy in ptr1; value in ptr2 unchanged ptr2.get_ptr_val(); // returns 0 cout << "(2) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl; ptr1.set_int(0); // changes val member only in ptr1 ptr2.get_int(); // returns 42 ptr1.get_int(); // returns 0 cout << "(3) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl; int *ip = new int(42); // dynamically allocated int initialized to 42 HasPtr ptr(*ip, 10); // HasPtr points to same object as ip does delete ip; // object pointed to by ip is freed ptr.set_ptr_val(0); // ok: ptr has its own copy cout << "(4) ptr: " << ptr << endl; }