Manipulating a LinkedList - c++

Question

So, i'm attempting to create a LinkedList using dummy nodes, however, when running through the functionality of each function, I get errors when it comes to the overloaded brackets operator, which is suppose to returns the item at the given index: list[n] Though i'm not exactly sure what may be wrong with the code.
I've spent hours looking at why i'm getting errors when trying to run each function. Sorry the question is so vague, but I feel as though I'm missing something, or something is coded poorly that I can't seem to detect.
Here's the code.
#ifndef _LINKED_LIST_GUARD
#define _LINKED_LIST_GUARD 1
#include <iostream>
#include <string>
#include "ListInterface.h"
template <typename T>
class LinkedList : public ListInterface<T>
{
private:
// Created in order to keep track of list size
int count = 0;
public:
// Default contructor
LinkedList()
{
_head = new Node;
_tail = new Node;
_head->_next = _tail;
}
private:
//
// Private node class to facilitate linked list
//
class Node
{
public:
T _data;
Node* _next;
// Constructor: default
Node(T d = T{}, Node* n = nullptr) : _data(d), _next(n) {}
~Node() { _next = nullptr; }
};
//
// Prevent copying and assigning
//
LinkedList(const LinkedList& rhs) {}
const LinkedList& operator=(const LinkedList& rhs) {}
public:
//
// LinkedList instance variables; we use dummy head and tail nodes in this implementation
unsigned _size;
Node* _head;
Node* _tail;
// Returns the value that the head points to, sinze _head is a dummy node.
T& first() const
{
return _head->_next->_data;
}
// Adds an item to the LEFT side of the linked list
void push(const T& x)
{
// Creates a new node with the user input data.
Node* current = new Node;
current->_data = x;
//Sets the node next to this node to be equal to what the head was previously pointing to.
current->_next = _head->_next;
//Finally, sets the user created node to be the first node within the list, then adds to the count.
_head->_next = current;
count++;
}
T& operator[](unsigned n)
{
//Starts at position one, since this would never return zero.
int position = 1;
//If the user input value is greater than the amount of items in the list
if (n > count)
{
//Throws a string exception.
throw std::string("Invalid Positon");
}
//Loops through the LinkedList
for (Node* current = _head->_next; current != _tail; current = current->_next)
{
//If the node at the current position is equal to the user input value
if (position == n)
{
//returns the current positions data, since it would be the data at user input position
return current->_data;
}
// If not, adds to position, and checks again.
position++;
}
return _head->_data;
}
//uses the pop function over and over until the list is empty, leaving only the _head and _tail dummy nodes.
void clear()
{
do
{
pop();
} while (count != 0);
}
bool contains(const T& target) const
{
//Loops through the LinkedList.
for (Node* current = _head->_next; current != _tail; current = current->_next)
{
//While looping, if the current node's data is equal to the user input target data, returns true.
if (current->_data == target)
return true;
}
// If it never finds anything, returns false.
return false;
}
bool pop()
{
//The head would only point to the tail if the list were empty.
if (_head->_next == _tail)
{
std::cout << "Unable to pop, list is empty ";
return false;
}
if (_head->_next != _tail)
{
//Creates a new node that has its values equal to the first node within the list.
Node* deleteNode = _head->_next;
//Sets the front of the node to be equal to the first node after the heads next node.
_head->_next = _head->_next->_next;
//Finally, deletes the node that deleteNode points to, and reduces the count
delete deleteNode;
count--;
return true;
}
//If the pop is unsucessful, returns false.
return false;
}
T& last() const
{
// There can't be a last value if the list is empty, so throws an exception
if (_head->_next == _tail)
{
//throw std::string("List is empty.");
std::cout << "List is empty";
}
if (_head->_next != _tail)
{
for (Node* current = _head->_next; current != _tail; current = current->_next)
{
//Loops through the list until the node that points to tail is located, then returns it.
if (current->_next == _tail)
return current->_data;
}
}
return _tail->_data;
}
int search(const T& target = T{}) const
{
//Once again, starts a position 1, since 0 is not a valid position
int position = 1;
//Loops through list
for (Node* current = _head->_next; current != _tail; current = current->_next)
{
//While looping, if the current node's data is equal to the user input target, returns the position
if (current->_data == target)
{
return position;
}
//Otherwise increases the position, and loops again.
position++;
}
// If it is unable to find the target in the list, returns -1.
return -1;
}
bool isEmpty() const
{
// If the _head points to the tail, that means there are no nodes in between, meaning it is empty.
if (_head->_next == _tail)
{
return true;
}
//Otherwise, return false.
return false;
}
unsigned size() const
{
//Returns the count, which is altered by remove, pop, and push.
return count;
}
bool remove(const T& target)
{
//Creates a node, whose data is initially null.
Node* deleteNode = nullptr;
//Creates another node to follow behind it.
Node* trailer = _head;
//Finally, creates a node that is to represent the current node that is being pointed at.
Node* current = _head->_next;
//Loops
while (current != _tail && current->_data != target)
{
trailer = current;
current = current->_next;
}
//If the data is current is equal to the target
if (current->_data == target)
{
// Sets the node to be deleted to current
deleteNode = current;
//then, sets current to the node right after.
current = current->_next;
//Finally, sets the trailer to the current node, since it's no longer needed
trailer->_next = current;
//Then, simply delets the node, and subtracts from the count.
delete deleteNode;
count--;
return true;
}
else
// If it is unable to find the targeted value, returns false.
std::cout << "unable to remove, item not in list" << std::endl;
return false;
}
//
// Internal consistency check
//
public:
virtual bool check() const
{
bool sizeConsistent = isSizeConsistent();
bool headTailConsistent = isEndConsistent();
if (!sizeConsistent) std::cerr << "Size inconsistent" << std::endl;
if (!headTailConsistent) std::cerr << "Head / Tail inconsistent" << std::endl;
return sizeConsistent && headTailConsistent;
}
//
// Stated size is accurate to the entire list
//
bool isSizeConsistent() const
{
int count = 0;
for (Node* current = _head->_next; current != _tail; current = current->_next)
{
count++;
}
return size() == count;
}
//
// Checks that the head and tail are defaulted properly and the
// respective next pointers are appropriate.
//
bool isEndConsistent() const
{
if (_head->_data != T{}) return false;
if (_tail->_data != T{}) return false;
if (_head->_next == nullptr) return false;
if (_tail->_next != nullptr) return false;
if (isEmpty() && _head->_next != _tail) return false;
if (!isEmpty() && _head->_next == _tail) return false;
return true;
}
};
#endif
Any overall suggestions for a fix?