singleton.cpp

/*
* Copyright(c) 2019 Jiau Zhang
* For more information see <https://github.com/JiauZhang/algorithms>
* 
* This repo is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation
*
* It is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with THIS repo. If not, see <http://www.gnu.org/licenses/>.
*/

#include <iostream>

using namespace std;

class singleton_v1
{
public:
	int data_test;
	static singleton_v1& getInstance() {
		static singleton_v1 singleton;
		return singleton;
	}
private:	
	singleton_v1() {}
};

int main(int argc, char** argv)
{
	//使用返回值得引用才会发生使用的是同一个类实例 
	cout << "mysingleton1: ";
	singleton_v1& mysingleton1 = singleton_v1::getInstance();
	mysingleton1.data_test = 0;
	cout << mysingleton1.data_test << ' ';
	mysingleton1.data_test++;
	cout << mysingleton1.data_test << '\n';
	
	cout << "mysingleton2: ";
	singleton_v1& mysingleton2 = singleton_v1::getInstance();
	cout << mysingleton2.data_test << ' ';
	mysingleton2.data_test++;
	cout << mysingleton2.data_test << '\n';
	
	//直接将返回值赋值给声明的类变量，并不会使用同一个类的实例 
	cout << "mysingleton3: ";
	singleton_v1 mysingleton3 = singleton_v1::getInstance();
	cout << mysingleton3.data_test << ' ';
	mysingleton3.data_test++;
	cout << mysingleton3.data_test << '\n';
	
	cout << "mysingleton4: ";
	singleton_v1 mysingleton4 = singleton_v1::getInstance();
	cout << mysingleton4.data_test << ' ';
	mysingleton4.data_test++;
	cout << mysingleton4.data_test << ' ';
	cout << mysingleton4.data_test << ' ';
	mysingleton4.data_test++;
	cout << mysingleton4.data_test << '\n';

	cout << "mysingleton1: " << mysingleton1.data_test << '\n';
	cout << "mysingleton2: " << mysingleton2.data_test << '\n';	
	cout << "mysingleton3: " << mysingleton3.data_test << '\n';
	cout << "mysingleton4: " << mysingleton4.data_test << '\n';
	
	//从输出可以看出，实例1和实例2操作的是同一个实例
	//而实例3和实例4是实例1和实例2共同指向的实例的副本，并且各自有自己的数据
	//所以，只有使用类返回的引用才可以使用同一个类实例 
	
	return 0;
}