Linked lists

[Andym]

As I am trying to digest this solution, I am curious as to why there are 2 structs?
One named "Personnel" that holds the data for each node and then another that is named "List". Why wouldn't just the struct "personnel" work for everything?

Also, I initially considered making the read from file a separate function but since it is only used once, I figured it would work just as well in the same function as the open file function. But now after looking at it from a different perspective, it does look cleaner to have it in the switch function. It doesn't seem to get lost in all of the code.

Anyway, thanks for your advice and I hope that you don't tire of my seemingly endless questions. I am a "why" kind of guy who obsesses over why and how things work. I really appreciate the fact that you took time to explain your reasoning and I can follow your style of teaching. A lot of times, in tutorials and example code on various sites, there really is no accompanying explanation.

[dhayden]

Think of a linked list as a collection of objects, all of the same type, just like an array is a collection of objects. The difference is that an array has a fixed size and a linked list can grow at run time to whatever size you want, limited only by the size of memory.

I am curious as to why there are 2 structs?

There are several reasons:
- If you used one struct, then how would you represent an empty list? With a separate "root" pointer? But then you'd have to pass that pointer to most of the methods.
- What if you tried to apply a "list" function like delete to a node that was half-way through the list?

I initially considered making the read from file a separate function but since it is only used once, I figured it would work just as well in the same function as the open file function.
Certainly it would, but like I said, if you think of the design process as "how do I make doing the work easy?" then you'll end up writing code that is more flexible and better organized.

Good luck with the rest of the assignment.

[Andym]

well, ive been working on this for a few days, trying to digest this and assemble it. For some reason @ line 141, I am getting an out of scope error for the list.insertFromList function. I have tried moving the function up to the top of the code, I have tried calling this function a billion different ways (not really sure why its being called with a "." operator) and I am just missing something. I am sure that it is something small but my assignment is due Wednesday and I am starting to stress.

main:

	#include <string>
	#include <iostream>
	#include <fstream>
	#include <cstdlib>
	#include <sstream>
	#include "Assignment4a.h"
	
		void List::insertFromFile(istream &is)
	{
	    Personnel *node = new Personnel;
	    while (node->read(is)) {
		add(node);
		node = new Personnel;
	    }
	    delete node;		// couldn't read it. Delete it now.
	}						 //end insertFromFile

	// read from an open file, or any stream
	bool Personnel::read(istream &is)
	{
	    is >> firstName >> lastName >> jobTitle >> empStatus >> wage;
	    return is.good();
	}
	
	
	// print to open file or any stream
	void Personnel::print(ostream &os)
	{
	    os << firstName << endl;
	    os << lastName << endl;
	    os << jobTitle << endl;
	    os << empStatus << endl;
	    os << wage << endl;
	}
	
	
	// prompt and read from user on cin
	bool Personnel::fromUser()
	{
	    cout << "Enter person's data:" << endl;
	    cout << "First Name: ";
	    cin >> firstName;
	    cout << "Last Name: ";
	    cin >> lastName;
	    cout << "Job Title: ";
	    cin >> jobTitle;
	    cout << "Employments Status <F>ull or <P>art time: ";
	    cin >> empStatus;
	    cout << "Wage: ";
	    cin >> wage;
	    return cin.good();
	}
	
	void
	List::print(ostream &os)
	 //=======================================
	 // PRINT LIST CONTENTS
	 //=======================================
	{
	    Personnel *next_ptr;
	
	    next_ptr = root;
	
	    if (next_ptr == NULL) {
		os << "EMPTY LIST: No nodes to print...." << endl;
	    }						 //end if
	    else {
		while (next_ptr != NULL) {
		    next_ptr->print(os);  // use the print() method that we defined above
		    next_ptr = next_ptr->next;
		}					 //end while
	    }						 //end else
	}						 //end print_list
	
	 //=====================Add node by manual input.
	void List::add(Personnel * node)
	 //=========================================
	 // ADD A NEW NODE
	 //=========================================
	{
	    node->next = root;
	    root = node;
	};						 //end Personnel
	
	List::~List()
	{
	    // ADD CODE to delete all items in the list here.
	}
	

	
	 //GetFileName
 string getFileName()
 {
 string fileName;	
 cout << "Enter Name of file to open INCLUDING extension ::" << endl;
 cin >> fileName;
 //================test to make sure the fileName name has a txt extension
 string ext="";
for(int i = fileName.length()-1;i>fileName.length()-5;i--)
{
    ext += fileName[i];
}
//cout<<ext;
if(ext != "txt.")
 {
    cout<<"File name does not contain the proper extension, Please Enter Name of file to open INCLUDING extension :: " <<endl;
    cin >> fileName;
}//end if
 return fileName;
 }//end getFileName 
	
    void menu()
    {
 	//Personnel *head = NULL;
	char choice;
 	bool quit = false;
	while (!quit)
      {
 	cout << "*****MENU*****" << endl;
 	cout << "1. Add items from Text File" << endl;
 	cout << "2. Manually Add Item" << endl;
 	cout << "3. Print ALL associates" << endl;
 	cout << "4. Search and Print" << endl;
 	cout << "5. EXIT" << endl;
 	 cout << "Enter a menu choice: " << endl;
        cin >> choice;
        cout << endl;
        
  		switch (choice)
 		{
 			case '1':  {
		                 string fileName = getFileName();
		                 ifstream file;
		                 file.open(fileName.c_str());
		                 if (!file.is_open()) 
						 {
		                     cout << "File did not open." << endl;
		                     exit(EXIT_FAILURE);
		                 }// end if
		list.insertFromFile(file)
	                   }//end case 1
			 break;
			 
			case '2': cout << "Manually add items" << endl;
			 break;
			 
			case '3': cout << "Print ALL items" << endl;
			 break;
			 
			case '4': cout << "Function to search for and print an associate to screen" << endl;
			 break;
			 
			case '5': cout << "EXIT" << endl; 
			 quit = true;
			 break;  
		}//end switch
 	 	
// 		switch (choice)
// 		{
// 			case '1': head = insertFromFile(head);
//			 break;
//			 
//			case '2': head = add_node(head);
//			 break;
//			 
//			case '3': print_list(head);
//			 break;
//			 
//			case '4': cout << "Function to search for and print an associate to screen" << endl;
//			 break;
//			 
//			case '5': cout << "EXIT" << endl; 
//			 quit = true;
//			 break;  
//		}//end switch
	}//end while
 }//end menu

int main()
 { 
 //-----------variables
	menu();
	system("pause");
	return 0;
 }//end main 

Header:

 using namespace std;

struct Personnel
{
    Personnel() : next(NULL) {}  // always initialize next to NULL
    string firstName;
    string lastName;
    string jobTitle;
    char empStatus;
    double wage;
    Personnel *next;

    bool read(istream &is);	// read from an open file, or any stream
    void print(ostream &os);	// print to open file or any stream
    bool fromUser();		// prompt and read from user on cin
};


struct List {
    List() : root(NULL) {}

    // Delete all items in the list
    ~List();

    // Add a node to the front of the list. node MUST be allocated
    // via new. The List will be responsible for deleting it.
    void add(Personnel *node);
    void insertFromFile(istream &is);

    // Print the list to the stream
    void print(ostream &os);
private:
    Personnel *root;		// head of the list
};