Below code instantiates a derived singleton object based on environment variable. The compiler errors saying error C2512: 'Dotted' : no appropriate default constructor. I don't understand what the compiler is complaining about.

#include <stdlib.h>
#include <iostream>
#include <string>
using namespace std;
class Dotted;
class Singleton{
public:
    static Singleton instant(){
        if (!instance_)
        {
            char * style = getenv("STYLE");
            if (!style){
                if (strcmp(style,"dotted")==0)
                {
                    instance_ = new Dotted();
                    return *instance_; 
                }           
            }
            else{
                instance_ = new Singleton();
                return *instance_;
            }
        }
        return *instance_;

    }
    void print(){cout<<"Singleton";}
    ~Singleton(){};
protected:
    Singleton(){};
private:
    static Singleton * instance_;
    Singleton(const Singleton & );
    void operator=(const Singleton & );

};
class Dotted:public Singleton{
public:
    void print(){cout<<"Dotted";}
protected:
    Dotted();

};
Dotted::Dotted():Singleton(){}

int main(){

     Singleton::instant().print();
     cin.get();
}