c – 简单引用计数：智能指针

>如果我们使用NULL初始化对象：reference_count = -1 else reference_count = 1
> copy ctor和operator = increment reference_count
>析构函数递减reference_count并且如果没有对指向对象的其他引用则执行其删除.

这是我的代码：

#ifndef smart_pointer_H
#define smart_pointer_H

template < typename T > class smart_pointer
{
    private:
        T*    pointer;      
        int reference_count;    

    public:

        smart_pointer() : pointer(0),reference_count(-1) {}

        smart_pointer(T* p) : pointer(p)
        {
            if (p != NULL)
            {
                this->reference_count = 1;
            }

            else
            {
                this->reference_count = -1;
            }
        }

        smart_pointer(const smart_pointer <T> & p) : pointer(p.pointer),reference_count(p.reference_count + 1) {}
        bool operator == (const smart_pointer <T>& p) { return pointer == p.pointer; }
        bool operator != (const smart_pointer <T>& p) { return pointer != p.pointer; }


        ~ smart_pointer()
        {
            if(-- reference_count == 0)
        {
                std::cout << "Destructing: " << 'n';
                delete pointer;
            }
        }

        T& operator *  () { return *pointer; }
        T* operator -> () { return pointer; }

        smart_pointer <T> & operator = (const smart_pointer <T> & p)
        {
                if (this != &p)
                {
                    if( -- reference_count == 0)
                    {
                        delete pointer;
                    }

                        pointer = p.pointer;
                        reference_count = p.reference_count + 1;
                }

        return *this;
        }
};

这是我的测试代码,类样本存储2D点和两个指向任何其他2D点的指针.

template < typename T >
class smart_pointer;

class Point
{
private:
    double x,y;
    smart_pointer <Point> p1;
    smart_pointer <Point> p2;

public:
    Point(double xx,double yy): x(xx),y(yy) {this-> p1 = NULL; this->p2 = NULL;}
    Point(double xx,double yy,smart_pointer <Point> p1,smart_pointer <Point> p2): x(xx),y(yy) {this-> p1 = p1,this->p2 = p2; }
    double getX(){ return x;}
    double getY(){ return y;}
    void setX(double xx)  {this->x = xx;}
    void setY(double yy)  {this->y = yy;}
    void setP1(smart_pointer <Point> p1) {this->p1 = p1;}
    void setP2(smart_pointer <Point> p2) {this->p2 = p2;}

    void print()
    {
         std::cout << "x= " << x << " y= " << y << 'n';
         std::cout << "p1" << 'n';
         if (p1 != NULL)
         {
             p1->print();
         }
         std::cout << "p2" << 'n';
         if (p2 != NULL)
         {
            p2->print();
         }
         std::cout << 'n';
    }

};

2D点列表：

#include "Point.h"

class PointsList
{
private:
    std::vector <smart_pointer <Point> > points;

public:
    smart_pointer <Point> & operator [] ( int index ) {return points[index];}

public:
    void push_back(smart_pointer <Point> p) {points.push_back(p);}
    void erase(unsigned int index) {points.erase(points.begin() += index );}
    void printPoints()
    {
        std::cout << "List of points" << 'n';
        for (unsigned int i = 0; i < points.size();  i++)
        {
            points[i]->print();

        }

    }
};

测试代码：

#include "Point.h"
#include "PointsList.h"

int main()
{
    smart_pointer <Point> pb = NULL;
    pb = (new Point(0,0));
    smart_pointer <Point> p0(new Point(0,0));
    p0->print();
    smart_pointer <Point> p1(new Point(10,10));
    p1->print();
    smart_pointer <Point> p2(new Point(20,20));
    p2->print();
    smart_pointer <Point> p3(new Point(30,30));
    p3->print();

    smart_pointer <Point> pa(p3);
    p0->setP1(p2);
    p0->setP2(p3);
    p0->print();    
    p0 = p1;
    p0->print();
    p0->print();

    PointsList pl1;
    pl1.push_back(p0);
    pl1.push_back(p1);

    PointsList pl2;
    pl2.push_back(p2);
    pl2.push_back(p3);
    pl1.erase(0);
    pl1.printPoints();
    pl2.printPoints();
    return 0;
}

这种解决方案的优势或不足之处在哪里？如何为大量数据运行速度,转换,可能的继承问题等等.Thanx为您提供帮助.

我对这个例子还有一个问题：哪种类型的智能指针(共享,作用域)最适合这样的数据结构：

//Class with cross-references to points p1,p2
class PointTopo
{
private:
    double x,y;
    PointTopo * p1;
    Point * p2;

public:
    PointTopo(double xx,y(yy) {this-> p1 = NULL; this->p2 = NULL;}
    ...

};

//Class  with cross references: topological model for Delaunay triangulation
class Edge
{
   private:
      Point2D * start;
      Edge *next;
      Edge *previous;
      Edge *twin;
...
};

谢谢你的帮助…