quote:
Original post by DungeonMaster
For me, friend class should be avoided for it disrupts c++ privacy structure ...
No no no
Common misconception. If used wrongly, it can be a tool for evil, yes. But not always.
Observe this simplified setup for a linked list.
class LinkedListNode{private: LinkedListNode* next; LinkedListNode* prev; DataType* theData;};class LinkedList{private: LinkedListNode* first; LinkedListNode* last;public: DataType* GetFront(); DataType* GetBack();};
It is common to be able to ask a linked list for its first and last elements, as represented by the functions here. But those data elements are ''hidden'' away inside LinkedListNode. So how will LinkedList get to them?
Option 1: Make theData public.
This is obviously defeating the object of encapsulation if anything in the program can study the insides of your linked lists and change them at will.
Option 2: Make a GetData() accessor in LinkedListNode.
This might be your preferred option. But even now, -any- class or function has direct access to the internals of your linked list. If that data is a pointer to an object, it would be possible for someone to delete that object without your LinkedList knowing it is deleted, perhaps causing an error if your list assumes all its data pointers are valid.
Option 3: Make LinkedList a friend class to LinkedListNode.
Here, we have opened up LinkedListNode to -only one- other class. No-one else can interfere with it since it is private. LinkedList can interfere, but that''s ok since we deliberately made these 2 classes to work together. This is nearly always the preferred option.
Lesson ends
rintvars()\n");
mCPRVars.Printvars();
printf("Finished running CCcompute::Makevars()\n\n\n");
getch();
}
** Start of FILE: "compute.h" **
#ifndef _CCompute_
#define _CCompute_
class CCompute
{
public:
int iVar;
void Makevars(void);
};
#endif
** Start of FILE: "compute.cpp" **
#include "compute.h"
void CCompute::Makevars(void)
{
iVar = 10;
}
** Start of FILE: "prvars.h" **
#ifndef _CPRVars_
#define _CPRVars_
class CPRVars
{
public:
void Printvars(void);
};
#endif
** Start of FILE: "prvars.cpp" **
#include "prvars.h"
#include "compute.h"
CCompute prCompute;
void CPRVars:
