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Cannot find where the memory leak is

mlholder (77)
Hi all,

I'am slowly working on a program that takes adds, subtracts and multiplies polynomials. I'm trying to implement the polynomial as a singly linked list. However, I keep getting a memory leak and I'am sure that I am deleting the allocated memory as needed. I'am hoping someone with more experience than I can look at the code and provide any hints as to where and why this is happening. Also, why is it that when I click the Preview button, it never shows me what I'm about to post? Thank you for any and all help and for your time.

File: Node.h
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#ifndef NODE_H
#define NODE_H

class Node
{
	public:
		Node();
		Node(int);
		Node(int, int);
		Node(int, int, Node*);
		~Node();
		int getCoefficient() const;
		int getExponent() const;
		Node* getNext() const;
		void setCoefficient(int);
		void setExponent(int);
		void setNext(Node*);

	private:
		int coefficient;
		int exponent;
		Node *next;
		friend class LinkedList;
};

#endif


File: Node.cpp
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#include <iostream>
#include "Node.h"

Node::Node()
{

}

Node::Node(int coef) : coefficient(coef), exponent(0), next(nullptr)
{

}

Node::Node(int coef, int expo) : coefficient(coef), exponent(expo), next(nullptr)
{

}

Node::Node(int coef, int expo, Node *ptr) : coefficient(coef), exponent(expo), next(ptr)
{

}

Node::~Node()
{
	//delete next;
}

int Node::getCoefficient() const
{
	return (coefficient);
}

int Node::getExponent() const
{
	return (exponent);
}

Node* Node::getNext() const
{
	return (next);
}

void Node::setCoefficient(int coef)
{
	coefficient = coef;
}

void Node::setExponent(int expo)
{
	exponent = expo;
}

void Node::setNext(Node *ptr)
{
	next = ptr;
}


File: Linked List.h
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#ifndef LINKEDLIST_H
#define LINKEDLIST_H

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

class LinkedList
{
	public:
		LinkedList();
		LinkedList(const LinkedList&);
		~LinkedList();
		bool empty() const;
		friend std::ostream& operator<<(std::ostream&, const LinkedList&);

		friend std::istream& operator>>(std::istream&, LinkedList&);
		void insertHead(int);
		void insertHead(int, int);
		void append(int);
		void append(int, int);
		void remove(Node*);

	private:
		Node *head;
};

#endif


File: Linked List.cpp
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 #include <iostream>
#include <cstdlib>
#include <cctype>
#include <string>
#include "Node.h"
#include "Linked List.h"

LinkedList::LinkedList() : head(nullptr)
{

}

LinkedList::LinkedList(const LinkedList &list)
{
	head = nullptr;
	Node *iterator = list.head;

	while(iterator != nullptr)
	{
		append(iterator->getCoefficient(), iterator->getExponent());
		iterator = iterator->getNext();
	}
}

LinkedList::~LinkedList()
{
	while(!empty())
	{
		Node *temp = head;
		head = head->getNext();
		delete temp;
	}

	delete head;

	_CrtDumpMemoryLeaks();
}

bool LinkedList::empty() const
{
	return (head == nullptr);
}

std::ostream& operator<<(std::ostream &ostr, const LinkedList &list)
{
	for(Node *iterator = list.head; iterator != NULL; iterator = iterator->getNext())
	{
		//Output the first term
		if(iterator == list.head)
		{
			if(iterator->getExponent() == 0)
				ostr << iterator->getCoefficient();
			else if(iterator->getExponent() == 1)
				ostr << iterator->getCoefficient() << 'x';
			else
				ostr << iterator->getCoefficient() << "x^" << iterator->getExponent();
		}

		else //Output all other terms
		{
			if(iterator->getExponent() == 0)
			{
				if(iterator->getCoefficient() < 0)
					ostr << " - " << -(iterator->getCoefficient());
				else
					ostr << " + " << iterator->getCoefficient();
			}
			else if(iterator->getExponent() == 1)
			{
				if(iterator->getCoefficient() < -1)
					ostr << " - " << -(iterator->getCoefficient()) << 'x';
				else if(iterator->getCoefficient() == -1)
					ostr << " - x";
				else if(iterator->getCoefficient() == 1)
					ostr << " + x";
				else
					ostr << " + " << iterator->getCoefficient() << 'x';
			}
			else
			{
				if(iterator->getCoefficient() < -1)
					ostr << " - " << -(iterator->getCoefficient()) << "x^" << iterator->getExponent();
				else if(iterator->getCoefficient() == -1)
					ostr << " - x^" << iterator->getExponent();
				else if(iterator->getCoefficient() == 1)
					ostr << " + x^" << iterator->getExponent();
				else
					ostr << " + " << iterator->getCoefficient() << "x^" << iterator->getExponent();
			}
		}
	}

	return (ostr);
}

std::istream& operator>>(std::istream &istr, LinkedList &list)
{
	using namespace std;

	bool term(false), negate(false), foundCoef(false);
	int coef, expo;
	string expression;

	getline(cin, expression);

	for(int index = 0; index < expression.length(); index++)
	{
		//Coefficients
		if(isdigit(expression[index]))
		{
			foundCoef = true;
			int tempIndex = index;
			while(isdigit(expression[index]))
			{
				index++;
				if(index == expression.length())
				{
					coef = atoi(expression.substr(tempIndex, index - tempIndex).c_str());
					if(negate)
						coef = -coef;
					list.append(coef);
					return (istr);
				}
			}

			coef = atoi(expression.substr(tempIndex, index - tempIndex).c_str());
			if(negate)
			{
				coef = -coef;
				negate = false;
			}

			index--;
		}

		//Variables
		else if(isalpha(expression[index]))
		{
			if(!foundCoef)
				coef = 1;
			expo = 1;

			if(index == expression.length() - 1)
			{
				if(negate)
					coef = -coef;
				list.append(coef, expo);
				return (istr);
			}
		}

		//Exponents
		else if(expression[index] == '^')
		{
			index++;
			int tempIndex = index;
			while(isdigit(expression[index]))
			{
				index++;
				if(index == expression.length())
				{
					expo = atoi(expression.substr(tempIndex, index - tempIndex).c_str());
					if(negate)
						coef = -coef;
					list.append(coef, expo);
					return (istr);
				}
			}

			expo = atoi(expression.substr(tempIndex, index - tempIndex).c_str());
			index--;
		}

		//Term Dividers and Negative Signs
		else if( (expression[index] == '+') || (expression[index] == '-') )
		{
			if(expression[index] == '-')
			{
				negate = true;
				if(index > 0)
					term = true;
			}
			else
			{
				term = true;
			}

			if(term)
			{
				term = false;
				foundCoef = false;
				list.append(coef, expo);
			}
		}
	}

	return (istr);
}

void LinkedList::insertHead(int coef)
{
	Node *temp = new Node(coef);

	if(!empty())
		temp->setNext(head->getNext());

	head = temp;
}

void LinkedList::insertHead(int coef, int expo)
{
	Node *temp = new Node(coef, expo);

	if(!empty())
		temp->setNext(head->getNext());

	head = temp;
}

void LinkedList::append(int coef)
{
	Node *temp = new Node(coef);

	if(empty())
		insertHead(coef);
	else
	{
		Node *iterator = head;
		while(iterator->getNext() != nullptr)
			iterator = iterator->getNext();
		iterator->setNext(temp);
	}
}

void LinkedList::append(int coef, int expo)
{
	Node *temp = new Node(coef, expo);

	if(empty())
		insertHead(coef, expo);
	else
	{
		Node *iterator = head;
		while(iterator->getNext() != nullptr)
			iterator = iterator->getNext();
		iterator->setNext(temp);
	}
}

void LinkedList::remove(Node *ptr)
{
	if(empty())
		return;
	else
	{
		if(ptr == head)
			head = head->getNext();
		else
		{
			Node *iterator = head;
			while(iterator->getNext() != ptr)
				iterator = iterator->getNext();
			iterator->setNext(ptr->getNext());
		}

		delete ptr;
	}
}


File: Polynomial Operations.cpp
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#include <iostream>
#include "Linked List.h"

#define CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>

int main()
{
	using namespace std;

	char ch;
	LinkedList list;

	cout << "Enter a polynomial expression.\n";
	cin >> list;
	cout << endl;

	cout << list << endl;

	cin.get(ch);
	return 0;
}
Last edited on
helios (17504)
Your insertion is incorrect. You do
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temp = new Node;
if (!this->empty())
    temp->next = this->head->next;
this->head = temp;
This code leaks the head node. The correct insertion is
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temp = new Node;
//Assumption this->head == nullptr iff this->empty()
temp->next = this->head;
this->head = temp;
mlholder (77)
Thank you helios. I coded the insertion functions off the top of my head and didn't look back, thus assuming they were correct. Do you happen to know why, when I try to preview my posts, the only thing it shows is a blank post with my user name?
mlholder (77)
Ok, so after changing my head insertion functions, the debugger is still complaining about a memory leak. Any ideas?

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void LinkedList::insertHead(int coef)
{
	Node *temp = new Node(coef);

	if(!empty())
		temp->setNext(head);

	head = temp;
}


The constructor for the node is

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Node::Node(int coef) : coefficient(coef), exponent(0), next(nullptr)
{

}
mlholder (77)
After changing my insertion functions and also looking at the append functions, the memory leak was occuring due to calling new twice, once in the append function and once in the insertHead functions. Therefore the memory leak was coming from my append functions. I am posting this for anyone who is currently learning linked lists.
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