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Singleton example in C++
/*
* Example of a singleton design pattern.
* Copyright (C) 2011 Radek Pazdera
* This program 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, either version 3 of the License, or
* (at your option) any later version.
* This program 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 program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <iostream>
class Singleton
{
private:
/* Here will be the instance stored. */
static Singleton* instance;
/* Private constructor to prevent instancing. */
Singleton();
public:
/* Static access method. */
static Singleton* getInstance();
};
/* Null, because instance will be initialized on demand. */
Singleton* Singleton::instance = 0;
Singleton* Singleton::getInstance()
{
if (instance == 0)
{
instance = new Singleton();
}
return instance;
}
Singleton::Singleton()
{}
int main()
{
//new Singleton(); // Won't work
Singleton* s = Singleton::getInstance(); // Ok
Singleton* r = Singleton::getInstance();
/* The addresses will be the same. */
std::cout << s << std::endl;
std::cout << r << std::endl;
}

yeweishuai commented May 4, 2017 edited

If this is a header .h file, class implements should be written in .cpp file
Otherwise, compile error occurs.

CMLDMR commented Oct 4, 2017

Good Example to show singleton. Thank you.

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