Thread: Help with FIFO QUEUE

Originally Posted by R.Stiltskin

Here's the output I get after making the corrections I suggested to you:

Code:

one
4
two
4
three
4
four
4
three
8
four
8
five
8
six
8
seven
8
eight
8
seven
8
eight
8
nine
11
ten
11
eleven
11

which is exactly what your main() calls for. The numbers don't correspond to the node labels because you aren't printing nodeIDs, you're printing mNodeCounter which is always the ID of the LAST node added to the queue. If you want each nodeID, change printList() to print temp->getID instead.
Your QueueItem constructor, and Queue::remove(), Queue::eraseList() are all OK. So your printList() must still be bad (unless you changed & messed up something else).

here's what mine look like:

Code:

//member function definitions for class Date
#include <iostream> //allows program to output data on screen
using std::cout;
using std::endl;
using namespace std;

#include <iomanip>
using std::setfill;
using std::setw;

#include <cstring>
using std::string;
using std::strcpy;

#include "Queue.h"  //include definition of class Queue from Queue.h



//constructor
Queue::Queue()
{   
	mpHead = NULL;
	mpTail = NULL;
	mNodeCounter = 0;
}

void Queue::addItem(char *pData)
{
	//create and initialize new QueueItem dynamically
	QueueItem *pQI = new QueueItem(pData, ++mNodeCounter);

	if ( mpHead == 0 ){ //check for empty queue 
		mpHead = mpTail = pQI;}
		
	else{
		// link new item onto tail of list using mpTail pointer
		
		mpTail->setNext(pQI);
		mpTail = pQI;
		
	} 

}//end addItem function

//function removeItem
void Queue::removeItem()
{	
	
	if (mpHead == NULL){
		return;}
	else
	{
	QueueItem* temp = mpHead;
	mpHead = mpHead->getNext();
	delete temp;}
}

	

//end removeItem function

//Erase List
void Queue::eraseList()
{	
	while (mpHead != NULL)
	removeItem();
	mpHead = mpTail = NULL;
}//end eraseList function

//prints contents of queue
void Queue::printList()const 
{	
	QueueItem* temp = mpHead;  //assign mpHead to temporary QueueItem
	cout << mpHead->getData() <<"\t\t"<< mNodeCounter <<endl;
	temp = temp->getNext();
}//end printList function

//destructor
Queue::~Queue()
{
	eraseList();
}

Code:

//member function definitions for class QueueItem

#include  <iostream> // allows program to output data
using namespace std;

#include  <cstring> 

#include "QueueItem.h" // include definition of class QueueItem from QueueItem.h

//QueueItem constructor
QueueItem::QueueItem(char *pData, int id)
{	
	strncpy_s(mData, pData, 30);
	mNodeID = id;
	mpNext = NULL;
	
}// end constructor

void QueueItem::setNext(QueueItem *pItem)
{
	mpNext = pItem;
}// end setNext function


QueueItem* QueueItem::getNext()
{
	return  mpNext;
}//end getNext function

int QueueItem::getId()
{
	return mNodeID;
}//end getId function

const char* QueueItem::getData()
{
	return mData;
}//end getData function

Originally Posted by R.Stiltskin

As I said before, you still haven't fixed printList(). You need a loop to print every node.
I said last night:

Compare your original printList() with the new one. I didn't say you should eliminate the loop. I meant that in the loop you should be using temp instead of mpHead.

By the way, there's still something missing in removeItem(). It hasn't caused any errors yet because nothing in your program ever uses mpTail (you set values for it, but you never use those values). The problem is that if there is only 1 node in the list and you delete that node, mpTail is still pointing to that deleted node. You need an "else if" block that also sets mpTail to NULL when the last node is deleted.

here is the loop i did:

Code:

	QueueItem* temp = mpHead;  //assign mpHead to temporary QueueItem
	while (temp != NULL){
	cout << temp->getData() <<"\t\t"<< mNodeCounter <<endl;
	temp = temp->getNext();}

IT WORKS!!!!!! thank you man. do you know any extra reading material i can get so i can better understand this?

Originally Posted by jackfraust

here is the loop i did:

Code:

Queue::printlist() const
if ( mpHead == NULL)
return;
else {
QueueItem* temp = mpHead;
cout << mpNext->getData() << "\t\t" << mNodeCounter << endl;
temp = temp->getNext
}

loop should have word

for

or

while

in the code


Which loop you see here?