引用計數實現

在看More Effective C++時就有引用計數，如今本身實現了下。

完成計數的基類

/************************************************
*
*author:周翔
*e-mail:604487178@qq.com
*blog:http://blog.csdn.net/zhx6044
*
*
*************************************************/

#ifndef REFCOUNTER_H
#define REFCOUNTER_H

#include <iostream>

class RefCounter
{
public:
    RefCounter();
    virtual ~RefCounter() = 0;
    void plusOneRef();
    void minusOneRef();
    bool isShared() const;
private:
    int m_refCounter;
};

#endif // REFCOUNTER_H

/************************************************
*
*author:周翔
*e-mail:604487178@qq.com
*blog:http://blog.csdn.net/zhx6044
*
*
*************************************************/

#include "refcounter.h"

RefCounter::RefCounter():m_refCounter(1)
{
}

RefCounter::~RefCounter()
{

}

void RefCounter::plusOneRef()
{
    ++m_refCounter;

}

void RefCounter::minusOneRef()
{
    --m_refCounter;

}

bool RefCounter::isShared() const
{
    return m_refCounter > 1;
}

一個須要實現引用計數的類

/************************************************
*
*author:周翔
*e-mail:604487178@qq.com
*blog:http://blog.csdn.net/zhx6044
*
*
*************************************************/

#ifndef OBJECT_H
#define OBJECT_H

#include <cstring>

#include "refcounter.h"

class Object : public RefCounter
{
    friend Object operator +(const Object& _v1, const Object& _v2);
public:
    Object(const char* _value);
    virtual ~Object();
    Object(const Object& _v);
    const char* className() const;
private:
    char *pd;
};

#endif // OBJECT_H

/************************************************
*
*author:周翔
*e-mail:604487178@qq.com
*blog:http://blog.csdn.net/zhx6044
*
*
*************************************************/

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

Object::Object(const char *_value)
{
    pd = new char[strlen(_value) + 1];
    strcpy(pd, _value);
}

Object::~Object()
{
    if (!isShared()) {
        delete[] pd;
    }
}

Object operator +(const Object& _v1, const Object& _v2)
{
    return Object((std::string(_v1.pd) + _v2.pd).data());
}

Object::Object(const Object &_v)
{
    pd = new char[strlen(_v.pd) + 1];
    strcpy(pd,_v.pd);
}

const char* Object::className() const
{
    return pd;
}

一個實現引用判斷的外裹類模板，封裝了邏輯

/************************************************
*
*author:周翔
*e-mail:604487178@qq.com
*blog:http://blog.csdn.net/zhx6044
*
*
*************************************************/

#ifndef REFCOUNTERWAPPER_H
#define REFCOUNTERWAPPER_H

#include <iostream>


template <typename T>
class RefCounterWapper
{
public:
    RefCounterWapper(T *p);
    ~RefCounterWapper();
    RefCounterWapper(const T& _v);
    RefCounterWapper(const RefCounterWapper &_v);
    RefCounterWapper& operator =(const RefCounterWapper& _v);
    const T* operator ->() const;
    const T& operator *() const;
    T* operator ->();
    T& operator *();
private:
    T *pd;
};

template <typename T>
RefCounterWapper<T>::RefCounterWapper(T *p):pd(p)
{

}

template <typename T>
RefCounterWapper<T>::~RefCounterWapper()
{
    if (!pd->isShared()) {
        delete pd;
    } else {
        pd->minusOneRef();
    }

}

template <typename T>
RefCounterWapper<T>::RefCounterWapper(const T &_v)
{
    pd = new T(_v);
}

template <typename T>
RefCounterWapper<T>::RefCounterWapper(const RefCounterWapper &_v)
{
    pd = _v.pd;
    pd->plusOneRef();
}

template <typename T>
RefCounterWapper<T>& RefCounterWapper<T>::operator =(const RefCounterWapper& _v)
{
    if (this == &_v) return *this;
    pd->minusOneRef();
    if (!pd->isShared()) {
        delete pd;
    }
    pd = _v.pd;
    pd->plusOneRef();
    return *this;
}

template <typename T>
const T* RefCounterWapper<T>::operator ->() const
{
    return  pd;
}

template <typename T>
const T& RefCounterWapper<T>::operator *() const
{
    return *pd;
}

template <typename T>
T* RefCounterWapper<T>::operator ->()
{
    return  pd;
}

template <typename T>
T& RefCounterWapper<T>::operator *()
{
    return *pd;
}

#endif // REFCOUNTERWAPPER_H

供外部使用的具備計數功能的類

/************************************************
*
*author:周翔
*e-mail:604487178@qq.com
*blog:http://blog.csdn.net/zhx6044
*
*
*************************************************/

#ifndef REFCOUNTEROBJECT_H
#define REFCOUNTEROBJECT_H

#include "refcounterwapper.h"
#include "object.h"




class RefCounterObject
{
    friend RefCounterObject operator +(const RefCounterObject& _v1, const RefCounterObject& _v2);
public:
    RefCounterObject(const char* _v = "Object");
    virtual ~RefCounterObject();
    const char* className() const;
private:
    RefCounterObject(const Object& _v);
    RefCounterWapper<Object> pd;
};


RefCounterObject::RefCounterObject(const char *_v):pd(new Object(_v))
{

}


RefCounterObject::~RefCounterObject()
{

}

RefCounterObject operator +(const RefCounterObject& _v1, const RefCounterObject& _v2)
{
    return RefCounterObject((*_v1.pd) + (*_v2.pd));
}

RefCounterObject::RefCounterObject(const Object &_v):pd(_v)
{

}

const char* RefCounterObject::className() const
{
    return pd->className();
}

#endif // REFCOUNTEROBJECT_H

測試代碼

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

using namespace std;

int main()
{
    RefCounterObject v("zhou love cc");
    cout << v.className() << endl;
    RefCounterObject v2 = v;
    cout << v2.className() << endl;
    RefCounterObject v3(v2);
    cout << v3.className() << endl;
    RefCounterObject v4;
    cout << v4.className() << endl;
    v4 = v3;
    cout << v4.className() << endl;

    RefCounterObject v5 = v4 + v2;
    cout << v5.className() << endl;


}

5個對象共享了2個Object，它們保存的字符串的值，分別位zhou love cc和zhou love cczhou love cc。

用Valgrind分析了內存，沒有內存泄漏

分析Object的析構函數被調用幾回

5個對象有兩個Object對象，調用析構2次，

還有各一次是

RefCounterObject v4;
    cout << v4.className() << endl;
    v4 = v3;//析構v4開始的Object
    cout << v4.className() << endl;

    RefCounterObject v5 = v4 + v2;//+操做底層產生一個局部的Object
    cout << v5.className() << endl;

共享的是RefCounterWapper中pd這個指針指向的對象。

這幾個類的關係如圖