第27课 - 再论智能指针（上）

1、再论智能指针

思考

使用智能指针(SmartPointer)替换单链

表(LinkList)中的原生指针是否可行？

LinkList.h

#ifndef LINKLIST_H

#define LINKLIST_H

#include"List.h"

#include"Exception.h"

#include"SmartPointer.h"

namespace DTLib

template <typename T>

class LinkList : public List<T>

protected:

    struct Node : public Object

        T value;

        SmartPointer<Node> next;

};

    mutable struct : public Object  //保证内存布局一致

        char reserved[sizeof(T)];   //木有实际作用，仅仅占空间,保证内存布局和Node一样

        SmartPointer<Node> next;

    }m_header;

    int m_length;

    SmartPointer<Node> m_current;

    int m_step;

    Node* position(int i) const

        SmartPointer<Node> ret  = reinterpret_cast<Node*>(&m_header);

        for(int p=0;p<i;p++)

            ret = ret->next;

        return ret.get();

    virtual Node* create()

        return new Node();

    virtual void destroy(Node* pn)

        delete pn;

public:

    LinkList()

        m_header.next = NULL;

        m_length = 0;

        m_step = 1;

        m_current = NULL;

    bool insert(int i,const T& e)

        bool ret = (0 <= i)&&(i <= m_length);

        if(ret)

            SmartPointer<Node> node = create();

            if( node.isNull() )

                SmartPointer<Node> current = position(i);

                node->value = e;

                node->next = current->next;

                current->next = node;

                m_length++;

            else

                THROW_EXCEPTION(NoEnoughMemoryException,"No memory to insert new element ...");

        return ret;

    bool insert(const T& e)

        return insert(m_length,e);

    bool remove(int i)

        bool ret = (0 <= i)&&(i < m_length);

        if(ret)

            SmartPointer<Node> current = position(i);

            SmartPointer<Node> toDel = current->next;

            if(m_current.get() == toDel.get())

                m_current = toDel->next;    //游标指向下一个数据元素即可

            current->next = toDel->next;

            m_length--;

          //  destroy(toDel);

        return ret;

    bool set(int i,const T& e)

        bool ret = (0 <= i)&&(i < m_length);

        if(ret)

            position(i)->next->value = e;

        return ret;

    T get(int i) const

        T ret;

        if(get(i,ret))

            return ret;

        else

            THROW_EXCEPTION(IndexOutOfBoundsExpception,"Invalid parameter i to get element ...");

        return ret;

    bool get(int i,T& e) const

        bool ret = (0 <= i)&&(i < m_length);

        if(ret)

            e = position(i)->next->value;   //position 为 const 成员函数

        return ret;

    int find(const T& e) const

        int ret = -1;

        int i = 0;

        SmartPointer<Node> node = m_header.next;

        while( node.isNull() )

            if(node->value == e)

                ret = i;

                break;

            else

                node = node->next;

                i++;

        return ret;

    int length() const

        return m_length;

    void clear()

        while( m_header.next.isNull() )

            SmartPointer<Node> toDel = m_header.next;

            m_header.next = toDel->next;

            m_length--;

          //  destroy(toDel);

    bool move(int i,int step = 1)

        bool ret = (0 <= i)&&(i < m_length)&&(step > 0);

        if(ret)

            m_current = position(i)->next;

            m_step = step;

        return ret;

    bool end()

        return ( m_current.isNull());

    T current()

        if(!end())  //if( m_current != NULL )

            return m_current->value;

        else

            THROW_EXCEPTION(InvalidParameterException,"No value at current position ...");

    bool next()

        int i = 0;

        while((i < m_step) && !end())

            m_current = m_current->next;

            i++;

        return (i == m_step);

    ~LinkList()

        clear();    //构造函数析构函数不会发生多态，destroy调用的父类

};

#endif // LINKLIST_H

main.cpp

#include <iostream>

#include"LinkList.h"

using namespace std;

using namespace DTLib;

int main()

    LinkList<int> list;

    for(int i=0;i<5;i++)

        list.insert(i);

    for(list.move(0);!list.end();list.next())

        cout<<list.current()<<endl;

    return 0;

程序崩溃！！！

问题出在哪里？

- SmartPointer的设计方案

指针生命周期结束时主动释放堆空间

—片堆空间最多只能由一个指针标识

杜绝指针运算和指针比较

新的设计方案

是时候创建新的智能指针了！

新的设计方案

- Pointer是智能指针的抽象父类（模板）

纯虚析构函数virtual ~Pointer() = 0;

重载operator - > ()

重载operator * ()

2、编程实验

智能指针的新方案 Pointer.h SmartPointer.h

Pointer.h

SmartPointer.h

main.cpp

To be continued ...

思考：

如何实现SharedPointer使得多个智能指针对象可

以指向同—片堆内存，同时支持堆内存的自动释放？