friend

I saw this header fil in some code I downloaded :

Code:

---

class car
{
  friend void start();
  friend void resume();
}
void start();
void resume();

---

I dont understand the use of the friend, whats the difference in functionality between the above and the below code ?

Code:

---

class car
{
  void start();
  void resume();
}

---

Appreciate any input.

The friend function is non-menber function that has the right to access provate data members of the class it has been declared to be a friend.

in the second code the functions you wrote are normal member functions.

What exactly is it that you are not understanding?

Code:

---

//header file

class Ccar
{
  friend void Run(Ccar *);
  protected:
  Ccar(size_t Dummy = 0);
  ~Ccar();
  virtual void Routine() = 0;
  private:
  queue<Ccar *>rqueue;
};
void Run(Ccar *);


//source file
void Run(Ccar *obj)
{ 
    cout << "*Run*" << endl;
    rqueue.push(obj); <--- rqueue undeclared !!!!!!
}

---

Whats the problem here ?

Code:

---

// header fil
class Ccar
{
    queue<Ccar*>rqueue;
    void Run(Ccar*);
    friend void Run1(Ccar*);
    protected:
    Ccar(size_t Dummy = 0);
    ~Ccar();
    virtual void Routine() = 0;
};
void Run1(Ccar*);

//source file
void Ccar::Run(Ccar*obj)
{ 
    cout << "*Run*" << endl;
    cout << rqueue.empty() << endl;
}

void Run1(Ccar*obj)
{ 
    cout << "*Run1*" << endl;
    cout << rqueue.empty() << endl;
}

---

If I use Run then I get 'implicit declaration of fuction Run(...)'
If I use Run1 then I get 'rqueue undeclared'

What am I doing wrong here ?

Thanks for any input.