example201.cpp

Data Abstraction & Problem Solving with C++源码

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

struct Node
{  int item;
   Node *next;
}; // end struct

int main()
{

   string fileName = "numbers.txt";
   Node *head = NULL, *tail = NULL;

	// Creates a linked list from the data in a text 
	// file. The pointer variables head and tail are
	// initially NULL. fileName is a string that names
	// an existing external text file.

	ifstream inFile(fileName);
	int      nextItem;

	if (inFile >> nextItem)               // is file empty?
	{  // file not empty:
	   head = new Node;
	   // add the first integer to the list
	   head->item = nextItem;
	   head->next = NULL;
	   tail = head;

	   // add remaining integers to linked list
	   while (inFile >> nextItem)
	   {  tail->next = new Node;
	      tail = tail->next;
	      tail->item = nextItem;
	      tail->next = NULL;
	   }  // end while
	}  // end if

	inFile.close();

	// Assertion: head points to the first node of the
	// created linked list; tail points to the last
	// node. If the file is empty, head and tail are
	// NULL (list is empty).

   // traverse the list to the end, writing each item
   for (Node *cur = head; cur != NULL; cur = cur->next)
      cout << cur->item << " ";
   cout << endl;

   return 0;
}