appxe01.cpp

teach yourself C++ in 21 days 第五版

// ***********************************************
//    FILE:        Listing 13E.13
//    PURPOSE:    Demonstrate ilinked list
//    NOTES:
//
//  COPYRIGHT:  Copyright (C) 2000-04 Liberty Associates, Inc.
//                All Rights Reserved
//
// Demonstrates an object-oriented approach to
// linked lists. The list delegates to the node.
// The node is an abstract data type. Three types of
// nodes are used, head nodes, tail nodes and internal
// nodes. Only the internal nodes hold data.
//
// The Data class is created to serve as an object to
// hold in the linked list.
//
// ***********************************************
 
 
#include <iostream>
using namespace std;
 
enum { kIsSmaller, kIsLarger, kIsSame};
 
// Data class to put into the linked list
// Any class in this linked list must support two methods:
// Show (displays the value) and 
// Compare (returns relative position)
class Data
{
  public:
    Data(int val):myValue(val){}
    ~Data(){}
    int Compare(const Data &);
    void Show() { cout << myValue << endl; }
  private:
    int myValue;
};
 
// Compare is used to decide where in the list
// a particular object belongs.
int Data::Compare(const Data & theOtherData)
{
    if (myValue < theOtherData.myValue)
       return kIsSmaller;
    if (myValue > theOtherData.myValue)
       return kIsLarger;
    else
       return kIsSame;
}
 
// forward declarations
class Node;
class HeadNode;
class TailNode;
class InternalNode;
 
// ADT representing the node object in the list
// Every derived class must override Insert and Show
class Node
{
   public:
     Node(){}
     virtual ~Node(){}
     virtual Node * Insert(Data * theData)=0;
     virtual void Show() = 0;
   private:
};
 
// This is the node which holds the actual object
// In this case the object is of type Data
// We'll see how to make this more general when
// we cover templates
class InternalNode: public Node
{
   public:
     InternalNode(Data * theData, Node * next);
     ~InternalNode(){ delete myNext; delete myData; }
     virtual Node * Insert(Data * theData);
     // delegate!
     virtual void Show() { myData->Show(); myNext->Show(); }  
 
   private:
     Data * myData;  // the data itself
     Node * myNext;    // points to next node in the linked list
};
 
// All the constructor does is to initialize
InternalNode::InternalNode(Data * theData, Node * next):
myData(theData),myNext(next)
{
}
 
// the meat of the list
// When you put a new object into the list
// it is passed ot the node which figures out
// where it goes and inserts it into the list
Node * InternalNode::Insert(Data * theData)
{
 
    // is the new guy bigger or smaller than me?
    int result = myData->Compare(*theData);
 
 
    switch(result)
    {
    // by convention if it is the same as me it comes first
    case kIsSame:        // fall through
    case kIsLarger:    // new data comes before me
       {
          InternalNode * dataNode = new InternalNode(theData, this);
          return dataNode;
       }
 
    // it is bigger than I am so pass it on to the next
    // node and let HIM handle it.
    case kIsSmaller:
       myNext = myNext->Insert(theData);
       return this;
    }
    return this;  // appease MSC
}
 
 
// Tail node is just a sentinel
 
class TailNode : public Node
{
   public:
     TailNode(){}
     ~TailNode(){}
     virtual Node * Insert(Data * theData);
     virtual void Show() { }
 
   private:
 
};
 
// If data comes to me, it must be inserted before me
// as I am the tail and NOTHING comes after me
Node * TailNode::Insert(Data * theData)
{
    InternalNode * dataNode = new InternalNode(theData, this);
    return dataNode;
}
 
// Head node has no data, it just points
// to the very beginning of the list
class HeadNode : public Node
{
   public:
     HeadNode();
     ~HeadNode() { delete myNext; }
     virtual Node * Insert(Data * theData);
     virtual void Show() { myNext->Show(); }
   private:
     Node * myNext;
};
 
// As soon as the head is created
// it creates the tail
HeadNode::HeadNode()
{
 	myNext = new TailNode;
}
 
// Nothing comes before the head so just
// pass the data on to the next node
Node * HeadNode::Insert(Data * theData)
{
    myNext = myNext->Insert(theData);
    return this;
}
 
// I get all the credit and do none of the work
class LinkedList
{
   public:
     LinkedList();
     ~LinkedList() { delete myHead; }
     void Insert(Data * theData);
     void ShowAll() { myHead->Show(); }
   private:
     HeadNode * myHead;
};
 
// At birth, I create the head node
// It creates the tail node
// So an empty list points to the head which
// points to the tail and has nothing between
LinkedList::LinkedList()
{
    myHead = new HeadNode;
}
 
// Delegate, delegate, delegate
void LinkedList::Insert(Data * pData)
{
    myHead->Insert(pData);
}
 
// test driver program
int main()
{
    Data * pData;
    int val;
    LinkedList ll;
 
    // ask the user to produce some values
    // put them in the list
    for (;;)
    {
       cout << "What value? (0 to stop): ";
       cin >> val;
       if (val == 0)
          break;
       pData = new Data(val);
       ll.Insert(pData);
    }
 
    // now walk the list and show the data
    ll.ShowAll();
    return 0;  // ll falls out of scope and is destroyed!
}