NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/13956

Text File | 1996-08-05 | 6.3 KB | 275 lines

Path: unsw.edu.au!usenet
From: [e-mail] (Jeroen Dijkmeijer)
Newsgroups: comp.lang.c++
Subject: template problem
Date: 28 Mar 1996 05:51:59 GMT
Organization: Centre for Remote Sensing and GIS, UNSW.
Message-ID: <4jd9dv$[e-mail]>
Reply-To: [e-mail]
NNTP-Posting-Host: wideglide.geog.unsw.edu.au
Keywords: template, friend declaration.

Problem with templates and friend declaration
  G'day

I haven't much of C++ experience. But I'm studying hard to learn. At this moment I do have a problem with templates. The example is taken from Deitel & Deitel C++ how to program ch 15 pg 697

The files are listed below.


// file listnode.h
// List template definition

#ifndef LISTNODE_H
#define LISTNODE_H

template<class DATA_TYPE>
class ListNode {
  friend class List<DATA_TYPE>;
public:
  ListNode(const DATA_TYPE &); //constructor
  DATA_TYPE getData() const;
private:
  DATA_TYPE data;              // data
  ListNode *nextPtr;
};

template<class DATA_TYPE>
ListNode<DATA_TYPE>::ListNode(const DATA_TYPE &info)
{
  data = info;
  nextPtr = NULL;
}

template<class DATA_TYPE>
DATA_TYPE ListNode<DATA_TYPE>::getData() const
{ return data; }
#endif



// file list.h
// Template definition of a List class.

#ifndef LIST_H
#define LIST_H
#include <iostream.h>
#include <assert.h>
#include "listnode.h"

template<class DATA_TYPE>
class List {
public:
  List(); //constructor
  ~List(); //destructor
  void insertAtFront(const DATA_TYPE &);
  int removeFromFront(DATA_TYPE &);
  int isEmpty() const;
  int member(const DATA_TYPE &) const;
  void print() const;
private:
  ListNode <DATA_TYPE> *firstPtr;
  ListNode <DATA_TYPE> *lastPtr;
  ListNode <DATA_TYPE> *getNewNode(const DATA_TYPE &);
};

//---------------------------------------- member definitions for List
template<class DATA_TYPE>
List<DATA_TYPE>::List()
{firstPtr = lastPtr = NULL; }

// Destructor
template<class DATA_TYPE>
List<DATA_TYPE>::~List()
{
  for(int i=0;i<10;i++);
  if(!isEmpty()) {
    cout<<"Destroying nodes ... "<<endl;
    ListNode<DATA_TYPE> *currentPtr = firstPtr, *tempPtr;
    while (currentPtr != NULL) {
      tempPtr = currentPtr;
      cout <<"deleting "<< tempPtr->data << endl;
      currentPtr = currentPtr -> nextPtr;
      delete tempPtr;
    }
  }
  cout << "All nodes destroyed" << endl <<endl;
}

// Insert a node at the front of the list
template<class DATA_TYPE>
void List<DATA_TYPE>::insertAtFront(const DATA_TYPE &value)
{
  ListNode<DATA_TYPE> *newPtr = getNewNode(value);

  if (isEmpty())
    firstPtr = lastPtr = newPtr;
  else {
    newPtr->nextPtr = firstPtr;
    firstPtr = newPtr;
  }
}

template<class DATA_TYPE>
int List<DATA_TYPE>::removeFromFront(DATA_TYPE &info)
{
  if (isEmpty())
    return 0;
  else {
    ListNode<DATA_TYPE> *tempPtr = firstPtr;
    if (firstPtr == lastPtr)
      firstPtr = lastPtr = 0;
    else
      firstPtr = firstPtr->nextPtr;
    info = tempPtr->data;
    delete tempPtr;
    return 1;
  }
}  // RemoveFromFront(DATA_TYPE &info)

template<class DATA_TYPE>
int List<DATA_TYPE>::isEmpty() const {return firstPtr == NULL; }

template<class DATA_TYPE>
ListNode<DATA_TYPE> *List<DATA_TYPE>::getNewNode(const DATA_TYPE &value)
{
  ListNode<DATA_TYPE> *ptr = new ListNode<DATA_TYPE>(value);
  assert(ptr != 0);
  return ptr;
}  // getNewNode(const DATA_TYPE &data)

// Display the contents of the List
template<class DATA_TYPE>
void List<DATA_TYPE>::print() const
{
  if(isEmpty()) {
    cout << "The list is empty" << endl <<endl;
    return;
  }
  ListNode<DATA_TYPE> *currentPtr = firstPtr;
  cout << "The List is: ";
  while (currentPtr != 0) {
    cout <<currentPtr->data << ' ';
    currentPtr = currentPtr->nextPtr;
  }
  cout << endl << endl;
}

template<class DATA_TYPE>
int List<DATA_TYPE>::member(const DATA_TYPE &info) const {
  if(isEmpty()) return 0;
  else {
    ListNode<DATA_TYPE> *currentPtr = firstPtr;
    while(currentPtr != NULL) {
      if(currentPtr->data == info) return 1;
      currentPtr = currentPtr->nextPtr;
    }
    return 0;
  }
}
#endif


// file list_driver.cpp
#include <iostream.h>
#include "list.h"
#include "pair.h"

void testIntegerList();
void testPairList();

main()
{
  testIntegerList();
  testPairList();

  return 0;
}

void testIntegerList()
{
  cout << "testing a list of integer values" << endl;
  List<int> integerList;

  int choice, value;
  do {
    cout << "? ";
    cin >> choice;
    switch (choice) {
    case 1:
      cout << "Enter an integer: ";
      cin >> value;
      integerList.insertAtFront(value);
      integerList.print();
      break;
    case 2:
      cout << "Deleting a node"<<endl;
      integerList.removeFromFront(value);
      cout<<"The value was"<<value<<endl;
      break;
    case 3:
      cin>>value;
      if(integerList.member(value)) cout<<value<<"is element of list"<<endl;
      else cout<<value<<"is NOT a member of list"<<endl;
      break;
    }
  } while (choice != 4);
  cout << "End test of integerList" <<endl;
}

void testPairList()
{
  cout << "testing a list of pair values" << endl;
  List<Pair> pairList;

  int choice;
    Pair value;
  do {
    cout << "? ";
    cin >> choice;
    switch (choice) {
    case 1:
      cout << "Enter a pair: ";
      cin >> value;
      pairList.insertAtFront(value);
      pairList.print();
      break;
    case 2:
      cout << "Deleting a node"<<endl;
      pairList.removeFromFront(value);
      cout<<"The value was"<<value<<endl;
      break;
    case 3:
      cin>>value;
      if(pairList.member(value)) cout<<value<<"is element of list"<<endl;
      else cout<<value<<"is NOT a member of list"<<endl;
      break;
    }
  } while (choice != 4);
  cout << "End test of pairList" <<endl;
}

void instructions()
{
  cout<<"Your choices are:"<<endl;
  cout<<"1: Add an value to the list"<<endl;
  cout<<"2: remove head from the list"<<endl;
  cout<<"3: see if an entered value is member of the list"<<endl;
  cout<<"4: quit the whole damned program"<<endl<<endl;
  cout<<"Enter your choice (Please)"<<endl;
}

wideglide[~/c_programs/c++ ]6%CC -g -fullwarn -o list_driver list_driver.cpp
CC -g -fullwarn -o list_driver list_driver.cpp
"listnode.h", line 9: error(3133): expected an identifier
    friend class List<DATA_TYPE>;


"listnode.h", line 9: error(3358): invalid friend declaration
    friend class List<DATA_TYPE>;

2 errors detected in the compilation of "list_driver.cpp".
wideglide[~/c_programs/c++ ]7%