singleton class implementation

#include <iostream>

using namespace std;

class parent{
    private:
        int data;
        static parent* obj;
        parent(){
            // data=0;
        }
    public:
        static parent* getinstance(){
            if(obj==NULL){
                obj=new parent();
            }
            return obj;
        }
        void setvalue(int val){
            data=val;
        }
        void getvalue(){
            cout<<data<<endl;
        }

};
parent *parent::obj;

int main()
{
  parent* obj=obj->getinstance();
  obj->getvalue();
  obj->setvalue(5);
  obj->getvalue();
  return 0;
}