smart-ptr.cpp
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上传日期:2022-06-29
资源大小:356k
文件大小:3k
源码类别:
书籍源码
开发平台:
Visual C++
- #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
- }