Singleton without private constructor and static getInstance metod

Create SingletonFactory class. This class is the owner of the one Singleton instance. Add also a static switch "already created" and use this switch in constructor (public) to break the second and next Singleton initialization.

Code snippet below:

singleton.h 

#include <iostream

class Singleton {
public:
  Singleton() {
     if (exists_already) {
        std::cout << "You mustn't do that !" << std::endl;
        // failure action !!!
     }
     else {
       std::cout << "Singleton first init" << std::endl;
       exists_already = true;
     }
  }

  void singleAction() {
     std::cout << "Run single action" << std::endl;
  }

private:
  static bool exists_already;
};

SingleFactory.h

#include <singleton.h>

class SingleFactory {

  public:
    static Singleton *getInstance() {
      return &single;
    }

  private:
    static Singleton single;
};

SingleFactory.cpp
(pay attention that it keeps movables belonging to Singleton class)

#include <singlefactory.h>

Singleton SingleFactory::single;
bool Singleton::exists_already = false;

and finally the usage example
main.cpp

include <iostream>
#include <cstdlib>
#include <singlefactory.h>

using namespace std;

int main(int argc, char *argv[])
{
  Singleton *n = SingleFactory::getInstance();
  cout << "Hello, world!" << endl;
  n->singleAction();
  Singleton *nextS = new Singleton();
  Singleton singleS;


  return EXIT_SUCCESS;
}