scrptr.h

C++_Primer_Book_and_Code.rar 第四版C++ PRIMER的中英文对照书和源代码

/*
 * This file contains code from "C++ Primer, Fourth Edition", by Stanley B.
 * Lippman, Jose Lajoie, and Barbara E. Moo, and is covered under the
 * copyright and warranty notices given in that book:
 * 
 * "Copyright (c) 2005 by Objectwrite, Inc., Jose Lajoie, and Barbara E. Moo."
 * 
 * 
 * "The authors and publisher have taken care in the preparation of this book,
 * but make no expressed or implied warranty of any kind and assume no
 * responsibility for errors or omissions. No liability is assumed for
 * incidental or consequential damages in connection with or arising out of the
 * use of the information or programs contained herein."
 * 
 * Permission is granted for this code to be used for educational purposes in
 * association with the book, given proper citation if and when posted or
 * reproduced.Any commercial use of this code requires the explicit written
 * permission of the publisher, Addison-Wesley Professional, a division of
 * Pearson Education, Inc. Send your request for permission, stating clearly
 * what code you would like to use, and in what specific way, to the following
 * address: 
 * 
 * 	Pearson Education, Inc.
 * 	Rights and Contracts Department
 * 	75 Arlington Street, Suite 300
 * 	Boston, MA 02216
 * 	Fax: [phone]
*/ 

#include <cstddef>
using std::size_t;
#include "screen5.h"

//private class for use by ScreenPtr only
class ScrPtr {
    friend class ScreenPtr;
    Screen *sp;
    size_t use;
    ScrPtr(Screen *p): sp(p), use(1) { }
    ~ScrPtr() { delete sp; }
};

class ScreenPtr {
public:
    // no default constructor: ScreenPtrs must be bound to an object
    ScreenPtr(Screen *p): ptr(new ScrPtr(p)) { }

    // copy members and increment the use count
    ScreenPtr(const ScreenPtr &orig):
       ptr(orig.ptr) { ++ptr->use; }
    ScreenPtr& operator=(const ScreenPtr&);

    // if use count goes to zero, delete the ScrPtr object
    ~ScreenPtr() { if (--ptr->use == 0) delete ptr; } 

    // constructor and copy control members as before
    Screen &operator*() { return *ptr->sp; }
    Screen *operator->() { return ptr->sp; }

    const Screen &operator*() const { return *ptr->sp; }
    const Screen *operator->() const { return ptr->sp; }
private:
    ScrPtr *ptr;        // points to use-counted ScrPtr class
};

ScreenPtr& ScreenPtr::operator=(const ScreenPtr &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 ScrPtr object
    return *this;
}