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/*

* 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;

}