singleton class with example.......

[madankumar]

#include <iostream>
using namespace std ;
 
class Singleton 
{
public:
// Implement the logic here to instantiate the class for the first time by validating the 
// member pointer. If member pointer is already pointing to some valid memory it means
// that the first object is created and it should not allow for the next instantiation
// so simply return the member pointer without calling its ctor. 
static Singleton* Instance();
 
protected:
 
// Default ctor, copy-ctor and assignment operators should be as private so that nobody
// from outside can call those functions and instantiate it
 
Singleton();
Singleton(const Singleton&);
Singleton& operator= (const Singleton&);
 
private:
// A member pointer to itself which point to the firstly created object and this should be
// returned if another object is instantiated that means the second object what you 
// thought of created is nothind but the first instance
 
static Singleton* pinstance;
};
 
Singleton* Singleton:instance = 0;// initialize pointer
Singleton* Singleton::Instance () 
{
if (pinstance 0) // is it the first call?
{ 
pinstance = new Singleton; // create sole instance
}
return pinstance; // address of sole instance
}
Singleton::Singleton() 
{ 
//... perform necessary instance initializations 
cout << "Hellow\n" ;
}
 
 
int main( )
{
Singleton *p1 = Singleton::Instance();
Singleton *p2 = p1->Instance();
Singleton & ref = * Singleton::Instance();
 
return 0 ;
}

[WolfPack]

You got a problem with this code?

[madankumar]

:p Hi Dear

you try with this code

#include <iostream>
using namespace std;
class Singleton
{
private:
static bool instanceFlag;
static Singleton *single;
Singleton()
{
//private constructor
}
public:
static Singleton* getInstance();
void method();
~Singleton()
{
instanceFlag = false;
}
};
bool Singleton::instanceFlag = false;
Singleton* Singleton::single = NULL;
Singleton* Singleton::getInstance()
{
if(! instanceFlag)
{
single = new Singleton();
instanceFlag = true;
return single;
}
else
{
return single;
}
}
void Singleton::method()
{
cout << "Method of the singleton class" << endl;
}
int main()
{
Singleton *sc1,*sc2;
sc1 = Singleton::getInstance();
sc1->method();
sc2 = Singleton::getInstance();
sc2->method();
return 0;
}

[~s.o.s~]

Hmm.. hey buddy is there a problem with your code or you want to submit an example to help others out ?

[gurucode]

Idid some changes to the first one. it is worked.

#include <iostream.h>
//using namespace std;

class Singleton {

public:

// Implement the logic here to instantiate the class for the first time by validating the
// member pointer. If member pointer is already pointing to some valid memory it means
// that the first object is created and it should not allow for the next instantiation
// so simply return the member pointer without calling its ctor.

static Singleton* Instance();

protected:
// Default ctor, copy-ctor and assignment operators should be as private so that nobody
// from outside can call those functions and instantiate it


Singleton();
Singleton(const Singleton&);
Singleton& operator= (const Singleton&);

private:

// A member pointer to itself which point to the firstly created object and this should be
// returned if another object is instantiated that means the second object what you
// thought of created is nothind but the first instance

static Singleton* pinstance;

};

Singleton* Singleton::pinstance(0);

// initialize pointerS

Singleton* Singleton::Instance ()
{
if (pinstance==0)  // is it the first call?
{

pinstance = new Singleton();
// create sole instance

}

return pinstance;

// address of sole instance
}

Singleton::Singleton()
{
//... perform necessary instance initializations
cout <<"Hellow\n" ;
}


int main( )
{

Singleton *p1 = Singleton::Instance();
Singleton *p2 = p1->Instance();
Singleton & ref = * Singleton::Instance();
return 0 ;
}