设计模式之单例模式

#include<iostream>
using namespace std;
#include<string>

//单例模式
//控制某个对象个数，只有一个

//实现单例的步骤
//1.构造函数的私有化
//2.增加静态私有的当前类指针
//3.提供静态的对外接口，可以让用户获得单例对象
    
//单例分为懒汉式和饿汉式，在类外初始化的时候可看出不同

//懒汉式是多线程不安全的，因为在getInstance那里可能创建多个类

//懒汉式
class singleton_lazy{
private:
    singleton_lazy(){
        cout<<"lazy"<<endl;
    }
    static singleton_lazy* sl;
public:
    static singleton_lazy* getInstance(){
        if(sl==NULL){
            sl=new singleton_lazy;
        }
        return sl;
    }
};
//类外初始化    
singleton_lazy* singleton_lazy::sl=NULL;


//饿汉式
class singleton_hungry{
private:
    singleton_hungry(){
        cout<<"hungry"<<endl;
    }
    static singleton_hungry* sh;
public:
    static singleton_hungry* getInstance(){
        return sh;
    }
};
//类外初始化    
singleton_hungry* singleton_hungry::sh=new singleton_hungry;


void test1()
{
    singleton_lazy* p1=singleton_lazy::getInstance();
    singleton_lazy* p2=singleton_lazy::getInstance();
    if(p1==p2){
        cout<<"lazy is singleton"<<endl;
    }
    else{
        cout<<"lazy is not singleton"<<endl;
    }
    
    singleton_hungry* p3=singleton_hungry::getInstance();
    singleton_hungry* p4=singleton_hungry::getInstance();
    if(p3==p4){
        cout<<"hungry is singleton"<<endl;
    }
    else{
        cout<<"hungry is not singleton"<<endl;
    }
}
int main()
{
    test1();
    cout<<"main"<<endl;
    return 0;
}