C / C++ / MFC

class Derived: public Base {
//....
virtual void func (char * line) {
  Base::func(line);
  printf(line);
}

class Base
{
public:
    static Base& Instance()
    {
        ASSERT( Base::pInstance );
        return *Base::pInstance;
    }

    virtual void f(); 
    virtual void g();
    ...

protected:

    Base()
    {
        ...
    }
    
    // We don't need to implement this. Objects of class Base
    // are never copied. We just declare it to make sure, the
    // compiler does not produce one its own.
    Base( const Base& );

    static Base* pInstance;
};

class Derived : public Base
{
public:

     virtual void f();
     ...

    static void CreateTheInstance()
    {
        ASSERT( Base::pInstance == 0 );
        Base::pInstance = new Derived();
    }

protected:
    Derived()
    {
        ...
    }
};

int randn(int n)
{
  int r;
  while((r=rand())==RAND_MAX);
  return ((double)r/RAND_MAX)*(n+1);
}