class function access other private data member?

[michaelp]

Well, I am making a small game to test my C++ and get better at it too. ;D

What I want to know is: How can one class's function access another class's private data members?
Here is an example: (Not the code in my actual game, ignore any errors in the code)

code:

class Person { public:    void function(Enemy enemy1)    {       cout << "you attacked, the enemy now has " <<       //I want this function to access be able to access and change "dataMember" in the enemy class    } }; class Enemy { private:    int dataMember; };

[DIIST]

michaelp @ January 5th 2008 wrote:

Well, I am making a small game to my C++ and get better at it too. ;D

What I want to know is: How can one class's function access another class's private data members?
Here is an example: (Not the code in my actual game, ignore any errors in the code)

The whole point of private members is hide methods,&variables from anything outside the class. If you want to access the members just make them public or protected( can only be accessed withen the class and subclasses).

[md]

I am not completely certain as I have never tried (or read about it, shame on me...) but private members are always inaccessible. You could use protected member data though. Then you just need to make Person a friend class to Enemy.

However! An enemy is a person, so maybe you are looking at this in the wrong way and Enemy should be derived from Person?

[wtd]

In all likelihood md is correct with regards to Enemy being derived from Person. Of course, the assumes that an Enemy can only be a Person. Perhaps Enemy should be a purely virtual base class, and EnemyPerson should derive from both Person and Enemy.

[michaelp]

I'll try using protected data members first...

How do you make a class a friend of another class?

[md]

c++:

class foo { ... }; class bar { friend class foo; ... }

[OneOffDriveByPoster]

md @ Sat Jan 05, 2008 11:09 pm wrote:

I am not completely certain as I have never tried (or read about it, shame on me...) but private members are always inaccessible. You could use protected member data though. Then you just need to make Person a friend class to Enemy.

Afaik, a friend of a class can access private members of the class granting friendship.

[michaelp]

Okay, thanks, the friend class and protected data members worked.

[CodeMonkey2000]

Shouldn't enemy inherit person?

[md]

CodeMonkey2000 @ 2008-01-06, 2:47 pm wrote:

Shouldn't enemy inherit person?

It could, or as wtd pointed out on irc person could inherit enemy as not all enemies are persons.

I'm thinking I wouldn't be using such classes in anything I wrote; and definitely not friend functions accessing private data. Better class hierarchies make inheritance easy, and using friend functions/classes to access private data is almost always bad practice.

[wtd]

No no... I'm suggesting using both interface and implementation inheritance.