设计模式C++学习笔记之三（Singleton单例模式）

单例模式看起来也蛮简单的，就是在系统中只允许产生这个类的一个实例，既然这么简单，就直接贴代码了。更详细的内容及说明可以参考原作者博客：cbf4life.cnblogs.com。

3.1.解释

main()，大臣

CEmperor，需要单例的类

说明：很多大臣拜见的皇帝，只有一个。体现在面向对象方面，CEmperor定义一个静态指针，和一个静态函数，私有化构造函数、析构函数、构造函数复制、重载赋值语句。

注意：线程安全，采用互斥体的方式实现。

看代码：

//Emperor.h

#pragma once#include <iostream>using std::cout;using std::endl;using std::string;class CEmperor{public:    static CEmperor * GetInstance();    static void ReleaseInstance();    void EmperorInfo(void);    void SetEmperorTag(string tag);private:    CEmperor(void);    virtual ~CEmperor(void);    CEmperor(const CEmperor&);    CEmperor& operator=(const CEmperor&);    static CEmperor *m_pEmperor;    static HANDLE m_pMutex;    string m_EmperorTag;    class CGarbo    {    public:        CGarbo()        {            cout << "Create Garbo" << endl;        }        ~CGarbo()        {            cout << "Destroy Garbo" << endl;            if (NULL != m_pEmperor)            {                WaitForSingleObject(m_pMutex, INFINITE);                if (NULL != m_pEmperor)                {                    cout << "Remove instance" << endl;                    delete m_pEmperor;                    m_pEmperor = NULL;                }                ReleaseMutex(m_pMutex);            }            if (NULL != m_pMutex)            {                cout << "Delete mutex" << endl;                CloseHandle(m_pMutex);                m_pMutex = NULL;            }        }    };    static CGarbo m_Garbo;};//Emperor.cpp

#include "StdAfx.h"#include "Emperor.h"#include <iostream>using std::cout;using std::endl;using std::string;CEmperor* CEmperor::m_pEmperor = NULL;HANDLE CEmperor::m_pMutex = CreateMutex(NULL, FALSE, NULL);CEmperor::CGarbo CEmperor::m_Garbo;CEmperor::CEmperor(void){    cout << "Create CEmperor Instance" << endl;}CEmperor::~CEmperor(void){    cout << "Destroy CEmperor Instance and release its resource" << endl;}void CEmperor::EmperorInfo(void){    char msgBuffer[50] = { 0 };    sprintf_s(msgBuffer, 50, "皇ê帝?某3某3某3... ...(%s).", m_EmperorTag.c_str());    string msg(msgBuffer);    cout << msg.c_str() << endl;}CEmperor* CEmperor::GetInstance(){    if (NULL == m_pEmperor)    {        WaitForSingleObject(m_pMutex, INFINITE);        if (NULL == m_pEmperor)            m_pEmperor = new CEmperor();        ReleaseMutex(m_pMutex);    }    return m_pEmperor;}void CEmperor::ReleaseInstance(){    if (NULL != m_pEmperor)    {        WaitForSingleObject(m_pMutex, INFINITE);        if (NULL != m_pEmperor)        {            delete m_pEmperor;            m_pEmperor = NULL;        }        ReleaseMutex(m_pMutex);    }}void CEmperor::SetEmperorTag( string tag ){    m_EmperorTag = tag;}//Singleton.cpp
#include "stdafx.h"#include "Emperor.h"
void DoIt()
{
    CEmperor *pEmperor1 = CEmperor::GetInstance();    pEmperor1->SetEmperorTag("95");    pEmperor1->EmperorInfo();    CEmperor *pEmperor2 = CEmperor::GetInstance();    pEmperor2->EmperorInfo();    CEmperor *pEmperor3 = CEmperor::GetInstance();    pEmperor3->EmperorInfo();    CEmperor *pEmperor4 = pEmperor3;    pEmperor4->EmperorInfo();    CEmperor *pEmperor5 = NULL;    pEmperor5 = pEmperor4;    pEmperor5->EmperorInfo();    CEmperor::ReleaseInstance();
}
int _tmain(int argc, _TCHAR* argv[])
{
    DoIt();
    _CrtSetDbgFlag(_CRTDBG_LEAK_CHECK_DF | _CRTDBG_ALLOC_MEM_DF);    _CrtDumpMemoryLeaks();    return 0;}
单例模式比较简单，但在项目中使用的时候，需要明确只调用CEmperor的GetInstance函数来获取实例。在C#里有更简单的方法，那就是声明只读的静态变量，比C++简单多了。但C++更吸引人们去研究，这就是软件研发的乐趣吧。