Doesn't a derived class inherit the private member of its parent?

Hi all,

I've got a base class Character and a class Pacman derived from Character.
Character is defined as follows:

Code:

#ifndef CHARACTER_H
#define CHARACTER_H

#include <iostream>
#include <string>
#include "Position.h"

enum STATE { DEAD = 0, ACTIVE = 1, SUPER = 2 };

//Speed definitions
const double NORMAL = 1.0;
const double SLOW = 0.5;

class Character
{
public:
   Character();
   Character(std::string name, Position position, int state, double speed);
   virtual ~Character();
   virtual void move();
   virtual void draw();

private:
   std::string name;
   Position position;
   int state; // i.e. dead, active, super
   double speed;
};

#endif

Code:

#include "Character.h"

using namespace std;

Character::Character()
      : name(""), position(Position()), state(ACTIVE), speed(NORMAL)
{}

Character::Character(std::string name, Position position, int state, double speed)
      : name(name), position(position), state(state), speed(speed)
{}

Character::~Character()
{}

and Pacman is defined as follows:

Code:

#include "Pacman.h"

using namespace std;

Pacman::Pacman()
    : Character(), pillsTaken(0)
{ 
	position.setX(STARTING_XPOSITION);
	position.setY(STARTING_YPOSITION);
}

Pacman::Pacman(string name, Position position, int state,
	double speed, int pillsTaken)
    : Character(), pillsTaken(0)
{
	position.setX(STARTING_XPOSITION);
	position.setY(STARTING_YPOSITION);
}

and the compiler is giving me the following error:

c:\users\...\arcade\pacman.cpp(8) : error C2248: 'Character:: position' : cannot access private member declared in class 'Character'
c:\users\...\arcade\arcade\character.h(32) : see declaration of 'Character:: position'
c:\users\...\arcade\character.h(22) : see declaration of 'Character'

I thought that since Pacman is a child of Character, it will have its own copies of private attributes defined in Character. Is this not the case?

the "protected" keyword is similar to "private" but allows derived classes to access the variables and functions declared as such, which is what you would use in this case.

No, private means private (i.e. nobody else can see them).
If you want derived classes to have access to the variables then either call get/set functions in the base class or make the variables protected.
protected only gives derived classes access to the variables, but not the outside world.
Of course you could also make them public, but that would be very bad coding style.

Actually, you might not need to make position protected at all. For example, if the Position class has an appropriate constructor, you could just write:

Code:

Pacman::Pacman()
    : Character(std::string(), Position(STARTING_XPOSITION, STARTING_YPOSITION), ACTIVE, NORMAL),
        pillsTaken(0)
{
}

By the way, I am guessing that the Character class is supposed to be an abstract base class, hence move() and draw() should be pure virtual member functions. Oh, and classes intended to be base classes should have a virtual destructor.

Also, the STATE enum should belong to the Character class instead of being global. The same probably goes for the speed definitions (and if not, they should be declared extern and then defined in the source file).

Thanks laserlight, you're always so helpful!
I did include a virtual destructor for base class character though didn't I?
I have:
virtual ~Character();

isn't that the virtual destructor??

Thanks a bunch

Originally Posted by Canadian0469

isn't that the virtual destructor??

Yes, that is correct.

Originally Posted by laserlight

.
Also, the STATE enum should belong to the Character class instead of being global. The same probably goes for the speed definitions (and if not, they should be declared extern and then defined in the source file).

Right, but for the speeds, the compiler complains (I'm using VC++ 2005) if I move the constant speed definitions into the class declaration since they are not of integral types.

If I can't declare them in the class but they are only to be used for objects of type Character, what would be the correct way of providing the definitions?

>> If I can't declare them in the class
You can declare them in the class, you just can't define them there. Put

Code:

const double Character::NORMAL = 1.0;
const double Character::SLOW = 0.5;

in a source file with static const declarations in the class.

DOH!

...right

thanks!