Singleton模式

 1. Introduction

 

  This design pattern and methodology ensures that only one instance of the C++ class is instantiated. It assures that only one object is created and no more. It is often used for a logging class so only one object has access to log files, or when there is a single resource, where there should only be a single object in charge of accessing the single resource. The singleton pattern discussed here gives the class itself, the responsibility of enforcement of the guarantee that only one instance of the class will be allowed to be generated.

 

2. example

   singleton.h 代码如下：

  class Singleton{public:static Singleton * GetInstance();void output();void SetID(int id);private:int m_id;private:Singleton(int id);Singleton(Singleton const &);static Singleton * m_instance;};

 

singleton.cpp 代码如下：

#include "singleton.h"#include <iostream>using namespace std;Singleton * Singleton::m_instance = NULL;Singleton::Singleton(int id):m_id(id){}Singleton::Singleton(Singleton const & singleton){m_id = singleton.m_id;}Singleton * Singleton:: GetInstance(){if( m_instance == NULL)m_instance = new Singleton(0);return m_instance;}void Singleton::SetID(int id){m_id = id;}void Singleton::output(){cout<<"I am singleton, and my id is "<<m_id<<"/n";}

 

client.cpp 代码如下

#include "singleton.h"int main(){Singleton * instance1 = Singleton::GetInstance();Singleton * instance2 = Singleton::GetInstance();instance1->output();instance2->output();instance1->SetID(100);instance1->output();instance2->output();}

 

运行结果如下：

I am singleton, and my id is 0I am singleton, and my id is 0I am singleton, and my id is 100I am singleton, and my id is 100