Access data in a parent class.

**Queatrix** · 09-17-2006

How can I access varibles in a parent class?

Say I have CHILD_CLASS inside of PARENT_CLASS.
An I want a function in my CHILD_CLASS to access a varible in PARENT_CLASS.

How would I do that without saving that varible in a global to accessed externally?

**Prelude** · 09-17-2006

>How can I access varibles in a parent class?
The "correct" object-oriented way would be to provide a protected member function for accessing the variable that the child class can inherit.

>Say I have CHILD_CLASS inside of PARENT_CLASS.
Are you talking about an inheritance hierarchy or nesting? If it's the former then see my answer above. If it's the latter, make the "child" class a friend of the "parent" class and reconsider your terminology.

**Queatrix** · 09-17-2006

Yes, I am refering to "inheritance hierarchy".

>> The "correct" object-oriented way would be to provide
>> a protected member function for accessing the
>> variable that the child class can inherit.

I don't understand.

**twomers** · 09-17-2006

Code:

class parent
{
private:
	int d;

protected:
	virtual int get_d( void ) // prob doesn't need to virtual
	{
		return d;
	}

public:
	parent() : d( 42 ){}
};



class child : public parent
{
private:
	int x;

public:
	child() : x(0){}

	void whatever()
	{
		cout<< "Here's parent::d - " << get_d();
	}
};

int main( void )
{
	child df;

	df.whatever();
}

**Queatrix** · 09-17-2006

But what I had the exact same class in a class?

**jverkoey** · 09-17-2006

Then read Prelude's reply. All you have to do is implement a protected function in the parent class which returns the value of the variable you desire. Then call this function from the child class and you're done.

**Prelude** · 09-17-2006

>But what I had the exact same class in a class?
Why don't you show us what you have? I'm getting mixed signals.

**twomers** · 09-17-2006

I think he means something like:

Code:

class thing
{
	thing *variable;
};

going from his previous thread. SHow us what you got though.

**Queatrix** · 09-17-2006

Code:

class minimax
{
   public:
      minimax *ply;
      char board[9];
      int depth;
      void look_ahead(); 
};

void minimax::look_ahead()
{
      }

minimax my_ai;

This is what I have so far.

I trying to make my child minimax class (ply) to make it's depth varible the same as it's parent's plus 1.

**Prelude** · 09-17-2006

>I think he means something like:
Then it's not a problem. You can access the private members of an object of the same class, whether it's a member itself or the argument to a function:

Code:

class thing {
    thing *p;
    int i;
public:
    void foo1()
    {
        p->i = 321; // Just fine
    }

    void foo2 ( const thing& t )
    {
        t.p->i = 123; // Also fine
    }
};

**twomers** · 09-17-2006

>> I trying to make my child minimax class (ply) to make it's depth varible the same as it's parent's plus 1.

You gonna call the child the same as the parent? (I know this is don in real life, but I don't think it's ok in programming)

**Queatrix** · 09-17-2006

Code:

class minimax
{
   public:
      minimax();
      minimax *ply;
      char board[20];
      int depth;
      void override_depth(int); 
      void look_ahead(); 
};

minimax::minimax(){
   depth = ply.depth + 1;   }

void minimax::override_depth(int dna){
   depth = dna;   }

void minimax::look_ahead()
{
      }

Okay, this script has my parent access my child. But I need the child to access the parent, not the other way round.

>> You gonna call the child the same as the parent? (I know
>> this is don in real life, but I don't think it's ok in programming)

If this is the case, then an external varible will be the only thing I can do, right?

Also, should I not be trying to make my own minimax class, and just download one off some site?

**maxorator** · 09-17-2006

Originally Posted by twomers

>> I trying to make my child minimax class (ply) to make it's depth varible the same as it's parent's plus 1.

You gonna call the child the same as the parent? (I know this is don in real life, but I don't think it's ok in programming)

There is no child or parent, there is one class...

**JaWiB** · 09-17-2006

> Okay, this script has my parent access my child.

I think we have a confusion of terms here. It looks like you don't mean parent, as in base class; you mean the owner of a pointer to an instance of the same class.

Can you just do:

Code:

ply->depth = this->depth+1;

?

**Queatrix** · 09-17-2006

Hmm, that locks my program up.

Are you sure that ply->depth is the "parent"s varible rather than "child"s?

Thread: Access data in a parent class.

Thread Tools

Search Thread

Display

Access data in a parent class.

Similar Threads

gcc: Template class child can't directly access parent fields

deriving classes

Message class Need help befor 12am tonight

Dikumud

gcc problem