What is singleton design pattern

Question Posted / kiran

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What is singleton design pattern..

Answer / lokesh

Singleton design pattern is a a creational pattern to
dictate how and when objects get created and it's main
purpose is to ensure that a class has only one instance

Example:
#define NULL 0

class Singleton
{
private:
Singleton(Singleton&){}
Singleton& operator =(Singleton&);
int nValue;
static Singleton* pSingleton;
Singleton():nValue(10)
{
}
public:
static Singleton*Instance()
{

if(NULL == pSingleton)
{
pSingleton = new Singleton();
}
return pSingleton;
}
void setValue(int val)
{
nValue = val;
}
int getValue()
{
return nValue;
}
};
Singleton* Singleton::pSingleton = NULL;

int main(int argc, char* argv[])
{
Singleton *abc = NULL;
cout<<Singleton::Instance()->getValue()<<endl;
Singleton::Instance()->setValue(20);

Singleton *xyz = NULL;
cout<<xyz->Instance()->getValue()<<endl;
Singleton *sss = Singleton::Instance();
return 0;
}