Friendship classes

[frankowzki]

Hello!
im trying to make some friend class but im having some problems, here is my situation.

I've 3 files "main.cpp" "classA.h" "classB.h", this is about showing a matrix of "chars"

This is my "main.cpp"

#include <iostream>
#include "classA.h"
#include "classB.h"
using namespace std;

int main()
{
	class_A ca;
	class_B cb;

	ca.create();
	cb.init();
	cb.insert();

	ca.showmtrx();	
}

This is my "classA.h"

#include <iostream>

using namespace std;

class class_A
{
	public:
	   void create();
	   void showmtrx();

	   friend class Class_B;
	   
	private:
	   char matrix[40][55]; 
};


void class_A::create()
{
	for (int i=0;i<=39;i++)
	{
	   for (int j=0;j<=54;j++)
	   {
	      matrix[i][j]=' ';
	   }
	}
}


void class_A::showmtrx()
{
	for (int i=0;i<=39;i++)
	{
	   for (int j=0;j<=54;j++)
	   {
	      cout << matrix[i][j];
	   }
           cout << endl;
	}
}

And this is my "classB.h"

#include <iostream>

class class_B
{	
	public:
	   void init();
	   void insert();
	private:
	   char obj1;

};


void class_B::init()
{
	obj1 = 'A'; 
}

void class_B::insert()
{
	class_A ca;

	ca.matrix[20][20]=obj1;	
}

What i did, i think that classB can access to private members of class A, and it does compile but when i "showmtrx" it seems like the new value of matrix[20][20] doesnt changes, i mean it still showing blank space instead of 'A' char.

What can i do?
thanks

[ne555]

You don't understand the difference between a class and an object of that class.
Or you think that all variables are global.

void class_B::insert()
{
	class_A ca; //this is not the object that you created in main()

	ca.matrix[20][20]=obj1;	
}

[frankowzki]

Ahh kk, i get it, and how i modify the object i created in "main.cpp" in my classB file?
Is that possible?

[ne555]

http://cplusplus.com/doc/tutorial/functions2/

[frankowzki]

so i have to pass an "object" by reference? or a "private member of a class" by reference?
Im trying to google some but im a bit lost,

btw thank u for fast replies man