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Expertise: Intermediate
Language: C++

April 24, 2001

How to Force a C++ Class to Be a Singleton

The following example demonstrates how to have only one instance of a class at a time.

 
class MySingleTon
{
public:
	static MySingleTon * GetObject()
	{
		static MySingleTon obj;
		return &obj;
	}

	...
	//other interface functions here
	...

private:
	MySingleTon();

};

First, declare the constructor as private, so no one can create an instance. Next, declare a static method, like GetObject in the code above. Any client can use the only instance of the class, as shown below:

 
#include “MySingleton.h”

main()
{
 MySingleTon * pObject = MySingleton::GetObject();

 ... use the object...

MySingleTon * pAnother = MySingleton::GetObject();

Note that both pObject and pAnother points to the one and only instance of MySingleTon.