Analysis on Singleton class....

[A_Surender]

Dear Gurus,


Please clear my doubts. I have browsed this site regarding Singleton class, I got to know how singleton works. But there are lot of doubts raised against "Singleton Class".

class Singleton
{
private:
static bool instanceFlag;
static Singleton *single;
Singleton()
{
//private constructor
}
public:
static Singleton* getInstance();
void method();
~Singleton()
{
instanceFlag = false;
}
};

void main()
{
Singleton obj1Singleton;
Singleton *obj2Singleton = new Singleton();

// An object of Singleton class
//case 1:

obj1Singleton.methos();

//yet another object of singleton class
//case 2:
obj2Singleton -> method();


}

Q1) But i can create multiple objects of "Singleton" class and access "method" function.

please clear my doubt.....



Thank you in advance...


-Suren

[humptydumpty]

have a look for the Following Code. and same time static Singleton* getInstance(); in your Code. Because No where i found the defenation of this Function in you Code.

class MySingleton {
private:
	static MySingleton *myReference;
	MySingleton()
	{
	}
 
public:
	static MySingleton *getInstance()
	{
		if(myReference==NULL)
			myReference = new MySingleton();
 
		return myReference;
	}
};

have a look here for a Singelton Class .and go with following Link this will help you to understand Singelton Class Concept.and yes don't forget to delete your myReference after Performing your work.

http://www.codeguru.com/forum/showth...ingelton+Class

Thanx

[Kheun]

In addition to humptydumpty's example, you also have to declare the static pointer in the .cpp file.

// In .cpp file
// Not necessary requires to assign NULL because static variables are set to 0 by default.
MySingleton *MySingleton::myReference;

[A_Surender]

Using the above class definition for a Singleton class. how do i declare an instance in my Main function?


-Suren

[Kheun]

Call the getInstance() member function.

class MySingleton {
private:
	static MySingleton *myReference;
	MySingleton1()
	{
	}
 
public:
	static MySingleton *getInstance()
	{
		if(myReference==NULL)
			myReference = new MySingleton();
 
		return myReference;
	}
};

MySingleton *MySingleton::myReference;

int main()
{
	MySingleton *p = MySingleton::getInstance();
}

[A_Surender]

Kheun,

Can you tell me about copy constructor in c++?

-Suren

[humptydumpty]

Did u Checked all of this in MSDN or in Some Good Books. if not please have a look in MSDN for these things if still some problem search on code guru if still problem Post your code with your Doubt.

Thanx

[Kheun]

Kheun,

Can you tell me about copy constructor in c++?

-Suren

You can search through this forum. Here's one of the result.
http://www.codeguru.com/forum/showth...py+constructor

[A_Surender]

humptydumpty

Please don't mind, actually i could not understand the following line of code, in Singleton class example.
MySingleton *MySingleton::myReference;

[humptydumpty]

Never mind Dude . just One Simple Question how you Decalre a Static variable in your Class . Try this and you will Know thw answer .if Still problem Please let us know

Thanx

[Kheun]

humptydumpty

Please don't mind, actually i could not understand the following line of code, in Singleton class example.
MySingleton *MySingleton::myReference;

All non-const static member variables have to be declared in a .cpp file. Basically, the first part of the line, " MySingleton *" declares a pointer to MySingleton . The second part, "MySingleton::myReference" is the full-scope name of the pointer, which also tells us myReference is a member of MySingleton.