Singleton Template

[mohaps]

Singleton.h (this is all you need)

Code: Select all

#ifndef _Singleton_h_
#define _Singleton_h_

template<class T> class Singleton : public T
{
public:
	static T* getInstance();
	static void deleteInstance();
protected:
	Singleton() : T(){}
	virtual ~Singleton(){}
private:
	static Singleton *sInstance;
};

template<class T> Singleton<T>* Singleton<T>::sInstance = 0;
template<class T> T* Singleton<T>::getInstance()
{
	if(sInstance == 0)
	{
		sInstance = new Singleton();
		atexit(deleteInstance);
	}
	return sInstance;
}
template<class T> void Singleton<T>::deleteInstance()
{
	if(sInstance)
	{
		delete sInstance;
	}
	sInstance = 0;
}


#define SINGLETON_CLS(cls)	Singleton<cls>
#define GET_INSTANCE(cls)	(SINGLETON_CLS(cls)::getInstance())
#endif

Singleton.cpp (a simple cpp main demonstrating how to use the Singleton template

Code: Select all

#include "Singleton.h"
#include <iostream>
#include <ctime>
class Clock
{
public:
	const unsigned int currentTimeMillis() const
	{
		return (unsigned int)time(0);
	}
protected:
	Clock(){}
	virtual ~Clock(){}
};

using std::cout;
using std::endl;
int main(int argc,char **argv)
{

	cout<<"Current Time : "<<GET_INSTANCE(Clock)->currentTimeMillis()<<endl;
}

have fun

[cmoibenlepro]

sorry... but what is a singleton?

[mohaps]

A Singleton is a design pattern where you just want to have one instance of a class and share it among the users.

take a look at the Clock class in the example..

Clock is a singleton.. the same instance is shared everywhere

[bal]

It's a design pattern. A singleton class is a class where there is only once instance of. So when you use the getInstance() method you're always getting the same object (usefull for sharing data between classes etc.).

@mohaps, what's with the #define's ?

[jox]

Singelton is a "design pattern" that allows to make sure that only and exactly one instance of a specific class is ever created and used in the whole application regardles in which part of it and how often it gets requested.

[jox]

you where shootin' quicker bal

[buhatkj]

Very clever certainly, but macros are something I generally try to avoid....
I generally prefer cleaner inheritance relationships than using a template and macro as you have done here. I'm sure this is just my own personal style, so regardless, as I said, pretty clever
-Ted

[schick]

Sorry, obsolute.

[schick]

Very clever certainly, but macros are something I generally try to avoid....
I generally prefer cleaner inheritance relationships than using a template and macro as you have done here. I'm sure this is just my own personal style, so regardless, as I said, pretty clever
-Ted

I like the ::getInstance() singleton pattern.

[mohaps]

hey macros are pretty cool if you use them responsibly


the macro GET_INSTANCE(clsName) actually is shorthand for writing Singleton<clsName>::getInstance()