friend Example

Note: this example uses a common technique for implementing an iterator in Java and translates it to C++ for the purposes of demonstrating how the friend modifier works.

SortedList.h

#ifndef SORTEDLIST_H
#define SORTEDLIST_H
 
#include "Student.h"
 
class SortedList {
 
    friend class Iterator;
 
    public:
    
        SortedList();
        bool insert(Student *s);
        Student *find(int studentID);
        Student *remove(int studentID);
        void print() const;
 
    private:

        struct ListNode {    
            Student *student;
            ListNode *next;
        };

        ListNode *head; // pointer to first node in the list
};
 
#endif

Iterator.h

#ifndef ITERATOR_H
#define ITERATOR_H
 
#include "Student.h"
#include "SortedList.h"
 
class Iterator {
 
    public:
 
        Iterator(const SortedList &list);
        Student *next();
        bool hasNext();

    private:
 
        SortedList::ListNode *curr;
};
 
#endif
 

Iterator.cpp

 #include "Iterator.h"
using namespace std;
 
Iterator::Iterator(const SortedList &list) : curr(list.head) {  }
 
Student *Iterator::next() {
    if (!hasNext()) 
        return 0;
    Student *temp = curr->student;
    curr = curr->next;
    return temp;
}
 
bool Iterator::hasNext() {
    return curr != 0;
}

Code fragment that uses an Iterator

SortedList L1;
 
for (int i = 0; i < 10; i++)
    L1.insert(new Student(i));
 
Iterator iter(L1);
 
while (iter.hasNext()) {
    Student *student = iter.next();
    cout << student->getID() << " ";
}
cout << endl;