【数据结构】27_再论智能指针 （上）

SmartPointer 的设计方案

• 指针生命周期结束时主动释放堆空间
• 一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

• Poniter 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* ()

template <typename T>
class Pointer : public Object
{
public:
    Pointer(T *p = NULL);
    T *operator->();
    T &operator*();
    bool isNull();
    T *get();
    
protected:
    T *m_pointer;
};

编程实验：智能指针的新方案

文件：Pointer.h

#ifndef POINTER_H
#define POINTER_H

#include "Object.h"

namespace DTLib
{

template <typename T>
class Pointer : public Object
{
public:
    Pointer(T *p = nullptr) : m_pointer(p)
    {
    }

    T *operator-> ()
    {
        return m_pointer;
    }

    const T *operator-> () const
    {
        return m_pointer;
    }

    T &operator* ()
    {
        return *m_pointer;
    }

    const T &operator* () const
    {
        return *m_pointer;
    }

    bool isNull() const
    {
        return (m_pointer == nullptr);
    }

    T *get() const
    {
        return m_pointer;
    }

protected:
    T *m_pointer = nullptr;
};

}

#endif // POINTER_H

[重构] 文件： SmartPointer.h

#ifndef SMARTPOINTER_H
#define SMARTPOINTER_H

#include "Pointer.h"

namespace DTLib
{

template<typename T>
class SmartPointer : public Pointer<T>
{
public:
    SmartPointer(T *p = nullptr) : Pointer<T>(p)
    {
    }

    SmartPointer(const SmartPointer &obj) : Pointer<T>(nullptr)
    {
        this->m_pointer = obj.m_pointer;
        const_cast<SmartPointer&>(obj).m_pointer = nullptr;
    }

    SmartPointer &operator= (const SmartPointer &obj)
    {
        if (this != &obj)
        {
            T *pointer = this->m_pointer;

            this->m_pointer = obj.m_pointer;
            const_cast<SmartPointer&>(obj).m_pointer = nullptr;

            delete pointer;
        }

        return *this;
    }

    ~SmartPointer()
    {
        delete this->m_pointer;
    }
};

}

#endif // SMARTPOINTER_H

文件：main.cpp

#include <iostream>
#include "SmartPointer.h"

using namespace std;
using namespace DTLib;

class Test
{
public:
    int i = 10;

    Test()
    {
        cout << "Test()" << endl;
    }

    ~Test()
    {
        cout << "~Test()" << endl;
    }

};

int main()
{
    SmartPointer<Test> sp = new Test();
    SmartPointer<Test> spn;

    cout << sp->i << endl;

    spn = sp;

    cout << spn->i << endl;

    cout << sp.isNull() << endl;
    cout << spn.isNull() << endl;

    return 0;
}

输出：

Test()
10
10
1
0
~Test()

To be continued...

思考
如何实现 SharedPointer 使得多个智能指针对象能够指向同一片堆空间，同时支持内存的自动释放？

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