ms_handle.h

C++Primer 经典之作

/*
 * 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 <exception>
#include <stdexcept>

void handle_out_of_memory(const std::bad_alloc&) { }

template <class T> class Handle {
public:
    Handle(T *p = 0) try : ptr(p), use(new size_t(1)) { 
    } catch(const std::bad_alloc &e) { handle_out_of_memory(e); }

    // overloaded operators to support pointer behavior
    T& operator*();
    T* operator->();
    const T& operator*() const;
    const T* operator->() const;

    // copy control: normal pointer aliasing; but last Handle deletes the object
    Handle(const Handle& h): ptr(h.ptr), use(h.use) { ++*use; }
    Handle& operator=(const Handle&);
    ~Handle() { rem_ref(); }
private:
    T* ptr;
    size_t *use;
    void rem_ref() { if (--*use == 0) {delete ptr; delete use;} }
};

/*  workaround: MS Compiler doesn't support out of line definition
 *  of function try block for template class constructor
template <class T> Handle<T>::Handle(T *p)
try : ptr(p), use(new size_t(1)) 
{
     // empty function body
}  catch(const std::bad_alloc &e) 
       { handle_out_of_memory(e); }
*/

template <class T> 
inline
Handle<T>& Handle<T>::operator=(const Handle &rhs)
{
    ++*rhs.use;
    rem_ref();     // decrement use count and delete pointers if needed
    ptr = rhs.ptr;
    use = rhs.use;
    return *this;
}

template <class T> inline T& Handle<T>::operator*() 
{ 
    if (ptr) return *ptr; 
    else throw std::runtime_error
                   ("derference of unbound Handle"); 
}
template <class T> inline T* Handle<T>::operator->() 
{ 
    if (ptr) return ptr; 
    else throw std::runtime_error
                   ("access through unbound Handle");

}

template <class T> inline
const T& Handle<T>::operator*() const
{ 
    if (ptr) return *ptr; 
    else throw std::runtime_error("derference of unbound Handle");
}
template <class T> inline
const T* Handle<T>::operator->() const
{ 
    if (ptr) return ptr; 
    else throw std::runtime_error("access through unbound Handle");

}