单例模式的C++简单实现

深碍√TFBOYSˉ_ 2022-06-08 00:29 183阅读 0赞

## 一、懒汉模式 ##

具体例子如下：

/**
      *		懒汉式单例模式
      */
    
    #include <iostream>
    
    using namespace std;
    
    /* 定义Singleton类，用来表示单例模式 */
    class Singleton
    {
    public:
    	static Singleton *getInstance();
    private:
    	Singleton();
    	Singleton(const Singleton &other);
    	Singleton &operator=(const Singleton &other);
    
    	static Singleton *instance;
    };
    
    /* 实现Singleton类中的方法和静态数据成员 */
    Singleton *Singleton::getInstance()
    {
    	return instance;
    }
    
    Singleton::Singleton(){cout << "Singleton()" << endl;}
    Singleton::Singleton(const Singleton &other){cout << "Singleton(const Singleton &other)" << endl;}
    Singleton &Singleton::operator=(const Singleton &other){cout << "Singleton &operator=(const Singleton &other)" << endl;}
    
    Singleton *Singleton::instance = new Singleton();
    
    
    /* 程序入口 */
    int main()
    {
    	Singleton* s1 = Singleton::getInstance();
    	Singleton* s2 = Singleton::getInstance();
    	Singleton* s3 = Singleton::getInstance();
    
    	cout << "s1 address is " << s1 << endl;
    	cout << "s2 address is " << s2 << endl;
    	cout << "s3 address is " << s3 << endl;
    	
    	return 0;
    }

注意有内存泄漏。

## 二、饿汉模式 ##

具体实现如下：

/**
      *	饿汉式单例模式
      */
    
    #include <iostream>
    #include <pthread.h>
    
    using namespace std;
    
    /* 定义Singleton类，用来表示单例模式 */
    class Singleton
    {
    public:
    	static Singleton *getInstance();
    private:
    	Singleton();
    	Singleton(const Singleton &other);
    	Singleton &operator=(const Singleton &other);
    
    	static Singleton *instance;
    	static pthread_mutex_t mutex;
    
    	/* 定义一个内嵌类用于清除Singleton实例 */
    	class DestroySingleton
    	{
    	public:
    		~DestroySingleton();
    	};
    
    	static DestroySingleton destroyInstance;
    };
    
    /* 实现Singleton类中的方法和静态数据成员 */
    Singleton *Singleton::getInstance()
    {
    	if(NULL == instance)
    	{
    		pthread_mutex_lock(&mutex);			/* 上锁 */
    		if(NULL == instance)
    		{
    			instance = new Singleton();
    		}
    		pthread_mutex_unlock(&mutex);		/* 解锁 */
    	}
    	return instance;
    }
    
    Singleton::Singleton(){cout << "Singleton()" << endl;}
    Singleton::Singleton(const Singleton &other){cout << "Singleton(const Singleton &other)" << endl;}
    Singleton &Singleton::operator=(const Singleton &other){cout << "Singleton &operator=(const Singleton &other)" << endl;}
    
    Singleton *Singleton::instance = NULL;
    pthread_mutex_t Singleton::mutex = PTHREAD_MUTEX_INITIALIZER;
    Singleton::DestroySingleton Singleton::destroyInstance;
    
    
    /* 实现内部类DestroySingleton的析构函数 */
    Singleton::DestroySingleton::~DestroySingleton()
    {
    	if(NULL != Singleton::instance)
    	{
    		delete Singleton::instance;
    		Singleton::instance = NULL;		/* 防止野指针 */
    		cout << "~DestroySingleton()" << endl;
    	}
    }
    
    
    /* 程序入口 */
    int main()
    {
    	Singleton* s1 = Singleton::getInstance();
    	Singleton* s2 = Singleton::getInstance();
    	Singleton* s3 = Singleton::getInstance();
    
    	cout << "s1 address is " << s1 << endl;
    	cout << "s2 address is " << s2 << endl;
    	cout << "s3 address is " << s3 << endl;
    	
    	return 0;
    }

注意多线程的同步问题，加锁与解锁。