Triggering a breakpoint when running circular queue with single pointer

Question

#include <iostream>
#include "CLQueue.h"

struct LNode {
    int item;
    LNode* next;
};

CLQueue::CLQueue(){
    QRear = NULL;
}


CLQueue::~CLQueue() {
    makeEmpty();
}

void CLQueue::Enqueue(int newitem) {
    LNode* newNode; 
    if (QRear == NULL) {
        newNode = new LNode;
        newNode->item = newitem;
        QRear = newNode;
        newNode->next = newNode;
    }
    else {
        newNode = new LNode;
        newNode->item = newitem;
        newNode->next = QRear->next;
        QRear->next = newNode; 
    }
}

void CLQueue::Dequeue(int deleteItem) {

}

bool CLQueue::isEmpty(){
    if (QRear == NULL) {
        return true;
    }
    else {
        return false;
    }
}

void CLQueue::makeEmpty() {
    LNode* tempPtr;
    if (QRear == NULL) {   //If queue is empty already
        std::cout << "The queue is empty.";
    }
    while (QRear != NULL) {
        tempPtr = QRear->next;
        QRear = tempPtr->next;
        delete tempPtr;
    }
}

void CLQueue::printList() {
    LNode* printPtr; 
    std::cout << "(";
    if (QRear == NULL) {
        std::cout << "This queue is empty.";
    }
    else {
        printPtr = QRear->next;
        std::cout << printPtr->item;
        printPtr = printPtr->next;
        while (printPtr != QRear->next) {
            std::cout << ", " << printPtr->item;
            printPtr = printPtr->next;
        }
    }
    std::cout << ")" << std::endl;
}

I get a breakpoint error with "delete tempPtr" when trying to run makeEmpty() in my driver file. I'm trying to make a circular queue with a single pointer for a class and it is, of course, still a work in progress. I'm still hazy on how to handle deleting nodes in linked lists in the first place.

Thanks!

EDIT: This is the error I'm getting:

The thread 0x6a38 has exited with code 0 (0x0).
HEAP[DSHW2.exe]: Invalid address specified to RtlValidateHeap( 00C30000, 00C3FC48 )
DSHW2.exe has triggered a breakpoint.

Answer 1

while (QRear != NULL) {
    tempPtr = QRear->next;
    QRear = tempPtr->next;

You have no certitude that QRear->next aka tempPtr isn't null. This makes tempPtr->next UB.

You'd want

while (QRear != NULL) {
    tempPtr = QRear;
    QRear = QRear->next;
    delete tempPtr;
}