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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
* 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 <>.
#include <iostream>
class Singleton
/* Here will be the instance stored. */
static Singleton* instance;
/* Private constructor to prevent instancing. */
/* 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;
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

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.

thank you,very good

how to implement in header only library.

Is this implementation thread-safe?

Your implementation has a memory leak.

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