我想使用智能指针实现一个简单的引用计数。该变量pointer表示指向存储对象的指针，reference_count表示对象副本的总数。
- 如果我们使用 NULL 初始化一个对象：reference_count = -1 else reference_count = 1
- 复制 ctor 和 operator = 增加 reference_count
- 析构函数递减reference_count，如果没有其他对指向对象的引用，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，类示例存储 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';
}
};
二维点列表：
#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;
}
这种解决方案的优点或缺点在哪里？大量数据的运行速度如何，转换，继承可能出现的问题等。感谢您的帮助。
我对这个例子还有一个问题：哪种类型的智能指针（共享的，作用域的）最适合这种数据结构：
//Class with cross-references to points p1, p2
class PointTopo
{
private:
double x, y;
PointTopo * p1;
Point * p2;
public:
PointTopo(double xx, double yy): x(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...