chapter3-16.cpp

C++STL程序员开发指南

//文件名：CHAPTER3-16.cpp
// Template class for storing list elements
#include <iostream>
#include <string>
using namespace std;
template <class T>                          // Use template keyword
class ListElement //定义类ListElement,用于表示list对象
{
public:
    T data;
    ListElement<T> * next ;
    ListElement(T& i_d, ListElement <T>* i_n)
    : data(i_d),next(i_n) { }
    ListElement<T>* copy()               // copy includes all next elements
    {	return new ListElement(data,(next?next->copy():0));	}
};
template <class T> class ListIterator //定义类ListIterator,用于访问和操作list对象
{ public :
   //ListIterator(List<T>& l) ;
   T operator()() ;
   int operator++() ;
   int operator!() ;
 public:
	 ListElement<T>* rep ;
};
template <class T>T ListIterator<T>::operator() ()
{ if (rep) return rep->data;
  else 
  {    
	  T tmp ;    return tmp ;           // Default value  
  }
}
template <class T>int ListIterator<T>::operator++(){   if (rep)     rep = rep->next ;   return (rep != 0) ;}
template <class T>int ListIterator<T>::operator!(){   return (rep != 0) ;}
template <class T>class List //定义类List 
{public:
    friend class ListIterator<T> ;
    List();
    List(const List&);
	~List();
    List<T>& operator=(const List<T>&);
	// typical list ops
	T head();
    List<T> tail();
    void add(T&);
    friend ostream& operator<<(ostream&, const List<T>&);
public:
    void clear() ; // Delete all list elements
    ListElement<T>* rep ;
};
// Default Constructor
template <class T>
List<T>::List(){ 	rep = 0 ; }
// Copy Constructor
template <class T>List<T>::List(const List<T>& l){     rep = l.rep ? l.rep->copy() : 0 ;}
// Overloaded assignment operator
template <class T>List<T>& List<T>::operator=(const List<T>& l)
{  if (rep != l.rep)   {        clear() ;        rep = l.rep ? l.rep->copy() : 0 ;    }
    return *this ;
}
// Destructor
template <class T>List<T>::~List(){  clear() ;}
// Delete representation
template <class T>
void List<T>::clear()
{   while (rep)
    {   ListElement<T>* tmp = rep ;
        rep = rep->next ;
        delete tmp ;
    }
    rep = 0 ;
}
// Add element to front of list
template <class T>void List<T>::add(T& i){   rep = new ListElement<T>(i,rep) ;}
// Return head of list or default value of type T
template <class T>T List<T>::head(){ if (rep) return rep->data ; else {T tmp ; return tmp ;}}
// Return tail of list or empty list
template <class T>List<T> List<T>::tail()
{    List<T> tmp ;
     if (rep)
       if (rep->next) tmp.rep = rep->next->copy() ;
     return tmp ;
}
// Output operator
template <class T>ostream& operator<<(ostream& os, const List<T>& l)
{  if (l.rep)
   {  ListElement<T>* p = l.rep ;
      os << "( " ;
      while (p){ os << p->data << " " ;   p = p->next ; }
      os << ")\n" ;
  }
  else
  os << "Empty list\n" ;
  return os ;
}
int main()
{
   List<int> l ;            // Integer list
   cout << l ;
   int i=1;
   l.add(i) ;
   i=2;
   l.add(i) ;
   i=3;
   l.add(i) ;
   cout << "l is " << l << endl ;
   cout << "head of l is " << l.head() << endl ;
   List<int> m = l.tail() ;
   List<int> o ;
   o = m;
   i=4;
   m.add(i);
   cout << "m is " << m << endl ;
   cout << "o is " << o << endl ;
   List<char> clist ;                     // Character list
   char ch;
   ch='a';
   clist.add(ch);
   ch='b';
   clist.add(ch);
   cout << clist << endl ;
   List<string> ls ;                      // string List
   ls.add(string("hello")) ;
   ls.add(string("world")) ;
   cout << "List of strings" << endl ;
   cout << ls << endl ;
   List<List<int> > listlist ;    // List of lists of integer. Notice that lists of lists are possible
   listlist.add(o) ;
   listlist.add(m) ;
   cout << "List of lists of ints\n" ;
   cout << listlist << endl ;
   List<List<List<int> > > lllist ;    // List of lists of lists of integer
   lllist.add(listlist) ;
   lllist.add(listlist) ;
   cout << "List of lists of lists of ints\n" ;
   cout << lllist << "\n" ;
   List<List<string> > slist ;                      // List of list of strings
   slist.add(ls) ;
   slist.add(ls) ;
   cout << "List of lists of strings\n" ;
   cout << slist << "\n" ;
   return 0 ;
}