Having trouble with Linked List

**hkmixxa** · 08-08-2004

Hi I'm newbie on the linked list concept and I'm trying to write a program that can basically allow a user to store information into a linked list with the basic functions: append, delete, display, etc.

My header file:

Code:

 //Specification file for the ScheduleList class
#ifndef SCHEDULELIST_H
#define SCHEDULELIST_H
#include <iostream>

class ScheduleList
{
	private:
		struct ListNode
		{
			int number;
			ListNode *next;
		};

		
		ListNode *head;
	public:
		ScheduleList()
		{ head = NULL;}
		~ScheduleList();
		void appendNode(int);
		//void deleteNode();
	//	void displayList();
};
#endif

The Cpp file for it:

Code:

 //Implementation file for the ScheduleList class
#include "ScheduleList.h"
#include <iostream>
using namespace std;

void  ScheduleList::appendNode(int num)
{
	ListNode *newNode, *nodeptr;
	newNode = new ListNode;
	newNode->number = num;
	newNode->next=NULL;

	if(!head)
		head = newNode;
	else
	{
		nodeptr = head;
		while(nodeptr->next)
			nodeptr=nodeptr->next;
		nodeptr->next = newNode;
	}


}

and my Main cpp file:

Code:

//Linked List Project
//Notes - http://www.functionx.com/cpp/articles/linkedlist.htm
#include <iostream>
#include "ScheduleList.h"
using namespace std;


int main()
{
	ScheduleList student;
	student.appendNode(2);

	return 0;

}

Anyways, it's not much so far but that's because I'm trying to do little by little so that I can be sure that it is working.

Whenever I try and compile, it keeps giving me these same 3 error messages:

Code:

 main.obj : error LNK2001: unresolved external symbol "public: __thiscall ScheduleList::~ScheduleList(void)" (??1ScheduleList@@QAE@XZ)
main.obj : error LNK2001: unresolved external symbol "public: void __thiscall ScheduleList::appendNode(int)" (?appendNode@ScheduleList@@QAEXH@Z)
Debug/main.exe : fatal error LNK1120: 2 unresolved externals
Error executing link.exe.

I have read through many forums, but I am still clueless as to what exactly the problem is.

Any help is greatly appreciated. Thanks.

**quzah** · 08-08-2004

The linker is telling you that in the class definition you have declared a destructor, and a function called "appendNode", but there isn't code for either one of them.

Quzah.

**Salem** · 08-08-2004

You need to add "ScheduleList.cpp" to the project

Right-click in the edit window, and you should get "Add to project"

Then rebuild everything

**hkmixxa** · 08-08-2004

Thanks a lot for the help. My problem was that I did not create the code for the destructor yet and when I did, it was working properly.

I have another problem regarding the code for searching a text file. My program is able to add information, display, and save it to a text file, but I'm having trouble figuring out how to search the text file for a particular entry.

The entries in my text file look like this:

0843543 Intro to C++ HH117

I'm trying to implement a function to search the text file by the first value (ie: 0843543). I tried using a strcmp but it would not find the match.

The code for this was:

Code:

 void SearchClass()
{
	char input[7];
	char course[7];
	int i;
	cout<<"enter in course to search: ";
	cin>>course;

	fstream readfile;
	readfile.open("C:/WINDOWS/Desktop/class.txt", ios::in);
	readfile.getline(input, 7);

	while(!readfile.eof())
	{
		
		
		if(strcmp(course, input)==0)
		{cout<<"match";}
		else
		{cout<<"no match";}
		readfile.getline(input, 7);

	}
	readfile.close();

}

Once it finds the match I need to be able to delete it or change it. Thanks again for all the help.

**toysoldier** · 08-09-2004

I am a newbie , so I just guess this maybe error:

your ScheduleList.h

class ScheduleList
{
......
public:
ScheduleList()
{ head = NULL;}
~ScheduleList();
void appendNode(int);
//this variable defined maybe like this :
// void appendNode(int num),add 'num'.
.....
};#endif

**quzah** · 08-09-2004

Originally Posted by toysoldier

I am a newbie , so I just guess this maybe error:

your ScheduleList.h

That's what's known as a function prototype. When prototyping a function, be it in a class, or by itself, you are giving the basics of what the function is:

Code:

#include <iostream>

//Prototype a few functions, so we can use them before we define them.
void foo( int );
int bar( void );

int main( void )
{
    //Because both prototypes have been given, we can now call these
    //functions, because we know what type of parameters, name, and
    //return values they have, if any.
    int x = 5;

    foo( x );
    x = bar( );

    return 0;
}

//Now we will define the functions temselves.
void foo( int x )
{
    std::cout << "Our argument has the value of " << x << ".\n";
}

int bar( void )
{
    std::cout << "We will return 3, just for the heck of it.\n";
    return 3;
}

What's interesting about prototypes, is that we could have made the first
prototype be this:

Code:

void foo( int somevariablename );

And defined it as this:

Code:

void foo( int x )
{
    std::cout << "Our argument has the value of " << x << ".\n";
}

And the code would both compile, as well as be perfectly legal. The name of
the parameters may be omitted entirely, or called whatever you like (as long
as it's a legal variable name), because the prototype just cares what the type
of each argument is, not its name.

Quzah.

**quzah** · 08-09-2004

Originally Posted by hkmixxa

Thanks a lot for the help. My problem was that I did not create the code for the destructor yet and when I did, it was working properly.

I have another problem regarding the code for searching a text file. My program is able to add information, display, and save it to a text file, but I'm having trouble figuring out how to search the text file for a particular entry.

The entries in my text file look like this:

0843543 Intro to C++ HH117

I'm trying to implement a function to search the text file by the first value (ie: 0843543). I tried using a strcmp but it would not find the match.

...

Once it finds the match I need to be able to delete it or change it. Thanks again for all the help.

You'll have to do it one of a few ways:
1) read a "word" from the file and then use strcmp on it
2) read a "line" from the file, strip off the first word, and then use strcmp on it

That's how you'll get your comparison. strcmp compares the entire string, not just one word. So you will have to manually pull the word to compare. In this case, the "word" happens to be a number.

You could I suppose read the first "word" as a number, and then compare it, but I'd go for one of the first two options.

As for changing the item, that'll be a bit more difficult.

1) If the "word" you are replacing is exactly the same size, you can open the file in binary mode for both reading and writing, and seek to the spot where the word begins, and then write out the new word on top of it.

2) If not, you will have to reconstruct the entire file to change this word.
a) read the file into memory beyond the point you want to change
b) seek to the spot you want to change
c) write the change, as well as every thing else you've read into memory
d) truncate if it is too long.

a) read the file into memory
b) make the changes in memory
c) write a new file
d) get rid of the old one

Something along those lines.

Quzah.

**quzah** · 08-09-2004

ARRRGGG!! READ THE ANNOUNCEMENTS! YOU HAVE BEEN TOLD! There's nothing quite like wasting your time on a problem "helping someone", when they have already been helped because it's is a duplicate post!

Actually, I know you've been told, because you yourself in another post, stated that "you're posting too much, and you're 'sorry' BUT..."

Stop making multiple posts on the same topic.

Quzah.

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