Using exception classes. (urgent)

Ok so i have 2 programs due in 2 hours

I have everything working, or so i believe except throwing exceptions. I have no idea how to go about this and can not find anything useful. My teacher is long gone to bed lol so im in trouble

Anyone who could enlighten me on this would be a savior thank you. I understand what they need to do. Throwing and catching per-say. im just not sure on the actual code.

Here is the main program he provided. I realize this is long but I'm just flabbergausted on what to do

Code:

/* To compile this program, do the following
aCC olab10BSTreeMain.cpp BSTree.cpp
To execute with test data file
a.out < /nfshome/csal/public_html/spring.10/2170/olab10sp10.dat

uses exceptions
As always let me know if there are syntax errors in program
*/

#include <iostream>
#include "BSTree.h"
using namespace std;

int main()
{

   BSTree MyTree;			// A binary search tree used in examples

   // See what happens when an empty tree is printed
   cout << "An empty tree:" << MyTree << "*" << endl;
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
      cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }

   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
  
   cin >> MyTree;		// read's into
   cout << "Tree after first read: " << MyTree << endl;;
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
      cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }

   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }

   MyTree.Insert("into");  	// insert new root
   cout << "Tree after insert: " << MyTree << endl;;

   cin >> MyTree;		// read's insert
   cout << "Tree after second read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
      cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }

   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cin >> MyTree;		// read's into
   cin >> MyTree;		// read's link
   cin >> MyTree;		// read's list
   cout << "Tree after read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cin >> MyTree;		// read one string into the tree
   cout << "Tree after read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cin >> MyTree;		// read's next
   cin >> MyTree;		// read's last
   cout << "Tree after read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cout << "Inorder traversal: " << endl;
   MyTree.InOrderTraversal();
   cout << endl;
   cout << "Preorder traversal: " << endl;
   MyTree.PreOrderTraversal();
   cout << endl;
   cout << "Postorder traversal: " << endl;
   MyTree.PostOrderTraversal();
   cout << endl;

   cin >> MyTree;		// read's link
   cin >> MyTree;		// read's insurance
   cout << "Tree after read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cout << "Inorder traversal: " << endl;
   MyTree.InOrderTraversal();
   cout << endl;
   cout << "Preorder traversal: " << endl;
   MyTree.PreOrderTraversal();
   cout << endl;
   cout << "Postorder traversal: " << endl;
   MyTree.PostOrderTraversal();
   cout << endl;

   cin >> MyTree;		// read's help
   cin >> MyTree;		// read's insert
   cout << "Tree after read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cout << "Inorder traversal: " << endl;
   MyTree.InOrderTraversal();
   cout << endl;
   cout << "Preorder traversal: " << endl;
   MyTree.PreOrderTraversal();
   cout << endl;
   cout << "Postorder traversal: " << endl;
   MyTree.PostOrderTraversal();
   cout << endl;

   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cout << "Inorder traversal: " << endl;
   MyTree.InOrderTraversal();
   cout << endl;
   cout << "Preorder traversal: " << endl;
   MyTree.PreOrderTraversal();
   cout << endl;
   cout << "Postorder traversal: " << endl;
   MyTree.PostOrderTraversal();
   cout << endl;

   cin >> MyTree;		// read's justice
   cout << "Tree after read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cout << "Inorder traversal: " << endl;
   MyTree.InOrderTraversal();
   cout << endl;
   cout << "Preorder traversal: " << endl;
   MyTree.PreOrderTraversal();
   cout << endl;
   cout << "Postorder traversal: " << endl;
   MyTree.PostOrderTraversal();
   cout << endl;

   cin >> MyTree;		// read's just
   cout << "Tree after read: " << MyTree << endl; // This does inorder traversal
   cout << "Count: " << MyTree.Count() << endl;
   try
   {
     cout << "First String: " << MyTree.First() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   try
   {
     cout << "Last String: " << MyTree.Last() << endl;
   }
   catch (NonExistent myexception)
   {
     cerr << "There are data itemd in the tree" << endl; 
   }
   cout << "Inorder traversal: " << endl;
   MyTree.InOrderTraversal();
   cout << endl;
   cout << "Preorder traversal: " << endl;
   MyTree.PreOrderTraversal();
   cout << endl;
   cout << "Postorder traversal: " << endl;
   MyTree.PostOrderTraversal();
   cout << endl;

   // test copy constructor
   BSTree CopyTree(MyTree);
   cout << "Copy Tree: " << CopyTree << endl;;

   cout << "end of main"<<endl;
   return 0;
}

and here is the code im working on

Code:

#include <string>

using namespace std;

// THIS IS WHERE IM HAVING TROUBLE
class myexception
{
public:
	void NonExistent();
};

struct node 
{
	string data;
	node *left;
	node *right;
};


class BSTree
{
public:
	//Define deconstructor
	~BSTree();
	void  DestroyTree();

	void Insert(string);
	void Delete(string);
	void InOrderTraversal();
	void PreOrderTraversal();
	void PostOrderTraversal();
	int Count();
	string First();
	string Last();

private:
	void DestroyTree(node *current);
	void InOrderTraversal(node *current);
	void PreOrderTraversal(node *current);
	void PostOrderTraversal(node *current);
	int Count(node *current);
	string First(node *current);
	string Last(node *current);

	node *root;
};

void myexception::NonExistent()
{
	cerr << "Error";
}


BSTree::~BSTree()
{
	DestroyTree();
}

void BSTree::DestroyTree()
{
	DestroyTree(root);
}

void BSTree::DestroyTree(node *current)
{
  if (current != NULL)
  {
    DestroyTree(current->left);
	DestroyTree(current->right);
    delete current;
  }
}

void BSTree::Insert(string data)
{

	node *current = new node;
	node *parent = new node;

	current = root;
	parent = NULL;

	while (current != NULL)
	{
		parent = current;

		if (data < current->data)
		{
			current = current->left;
		}
		else
		{
			current = current->right;
		}
		}

		if (parent == NULL)
		{
			root->data = data;
		}
		else if (data < parent->data)
		{
			parent->left->data = data;
		}
		else
		{
			parent->right->data = data;
		}

}

//In order public and private functions
void BSTree::InOrderTraversal()
{
	if (root == NULL)
	{
		return;
	}
	else
	{
		InOrderTraversal(root);
	}
}

void InOrderTraversal(node *current)
{
	if (current == NULL)
	{
		return;
	}
	else
	{
		InOrderTraversal(current->left);
		cout << current->data;
		InOrderTraversal(current->right);
	}
}

//Post order public and private functions
void BSTree::PostOrderTraversal()
{
	if (root == NULL)
	{
		return;
	}
	else
	{
		PostOrderTraversal(root);
	}
}

void PostOrderTraversal(node *current)
{
	if (current == NULL)
	{
		return;
	}
	else
	{
		PostOrderTraversal(current->left);
		PostOrderTraversal(current->right);
		cout << current->data;
	}
}

//Pre order public and private functions
void BSTree::PreOrderTraversal()
{
	if (root == NULL)
	{
		return;
	}
	else
	{
		PreOrderTraversal(root);
	}
}

void PreOrderTraversal(node *current)
{
	if (current == NULL)
	{
		return;
	}
	else
	{
		cout << current->data;
		PreOrderTraversal(current->left);
		PreOrderTraversal(current->right);
	}
}

//Count functions
int BSTree::Count()
{
	if (root == NULL)
	{
		return 0;
	}
	else
	{
		Count(root);
	}
}

int Count(node *current)
{
	if (current == NULL)
	{
		return 0;
	}
	else
	{
	int count = 1;

	count += Count(current->left);

	count += Count(current->right);

	return count;
	}
}

//Print first functions
string BSTree::First()
{

	if (root == NULL)
	{
		return 0;
		//throw NonExistent();
	}
	else
	{
		First(root);
	}
}

//Print second functions
string First(node *current)
{
	if (current->left == NULL)
	{
		cout << current->left->data;
	}
	else
	{
		First(current->left);
	}
}

string BSTree::Last()
{

	if (root = NULL)
	{
		return 0;
		//throw NonExistent();
	}
	else
	{
		Last(root);
	}
}

string Last(node *current)
{
	if (current->right == NULL)
	{
		cout << current->right->data;
	}
	else
	{
		First(current->right);
	}
} 

void BSTree::Delete(string data)
{

	bool found = false;

    if (root == NULL)
	{
		//exception
	}

    node *current = new node;
    node *parent = new node;
    current = root;

    while(current)
    {
        if(current->data == data)
        {
            found = true;
            break;
        }
        else
        {
            parent = current;

            if(current->data ==data)
			{
                current = current->right;
			}
			else
			{
                current = current->left;
			}
        }
    }
    if(!found)
    {
        //exception
    }


    // 3 cases :
    // 1. We're removing a leaf node
    // 2. We're removing a node with a single child
    // 3. we're removing a node with 2 children

    // Node with single child
    if((current->left == NULL && current->right != NULL) || (current->left != NULL && current->right == NULL))
    {
        if(current->left == NULL && current->right != NULL)
        {
            if(parent->left == current)
            {
                parent->left = current->right;
                delete current;
            }
            else
            {
                parent->right = current->right;
                delete current;
            }
        }
        else // left child present, no right child
        {
            if(parent->left == current)
            {
                parent->left = current->left;
                delete current;
            }
            else
            {
                parent->right = current->left;
                delete current;
            }
        }
        return;
    }

    //We're looking at a leaf node
    if( current->left == NULL && current->right == NULL)
    {
        if(parent->left == current)
		{
            parent->left = NULL;
		}
		else
		{
            parent->right = NULL;
		}

		delete current;
        return;
    }


    //Node with 2 children
    // replace node with smallest value in right subtree
    if (current->left != NULL && current->right != NULL)
    {
        node *chkr = new node;
        chkr = current->right;
        if((chkr->left == NULL) && (chkr->right == NULL))
        {
            current = chkr;
            delete chkr;
            current->right = NULL;
        }
        else // right child has children
        {
            //if the node's right child has a left child
            // Move all the way down left to locate smallest element

            if((current->right)->left != NULL)
            {
                node *lcurr = new node;
                node *lcurrp = new node;
                lcurrp = current->right;
                lcurr = (current->right)->left;
                while(lcurr->left != NULL)
                {
                    lcurrp = lcurr;
                    lcurr = lcurr->left;
                }
                current->data = lcurr->data;
                delete lcurr;
                lcurrp->left = NULL;
            }
            else
            {
                node *tmp = new node;
                tmp = current->right;
                current->data = tmp->data;
                current->right = tmp->right;
                delete tmp;
            }

        }
        return;
    }

}

Have you read Exception Handling in C++ - C Programming.com

Originally Posted by tabstop

Have you read Exception Handling in C++ - C Programming.com

Yes i have and i guess im just not following it.

So since he uses this line in the .cpp file

catch (NonExistent myexception)

do i need something in the class called NonExistent?

what would the myexception be? something like myexception.NonExistent ??

like in this line

catch (DivideByZero divZero)

I see where DivideByZero comes from. buttt where does divZero come from?

im sorry im just super lost. everything i read doesnt make a lot of sense

Nonexistent is the type, myexception is the name of the variable of that type.

Originally Posted by tabstop

Nonexistent is the type, myexception is the name of the variable of that type.

gah man i understand what you are saying but im not grasping it AGRH! lol

can you type up an example...

if i did like
NonExistent.myexception();

would that work?

so my class

Code:

class myexception
{
     void NonExistent();
};

is this right ? not enough? do I need like a throw () in there somewhere.

I really appreciate any help man.

Compare and contrast (except it's mostly compare):

Code:

int i;

Code:

Nonexistent myexception;

Do you ever go around talking about int.this and int.that? Of course not. You can only talk about members of objects, not members of classes.

ARGGHH! lol i understand what you are saying. Im sorry but I just can't think how to implement it.

So is my class part right or am i really missing something?

and when i call the exception in the function.

would I do something like

NonExistent... < arghh idk >

I dont want you to just hand me an answer but can you give a example related more to my code?

Originally Posted by bleuz

ARGGHH! lol i understand what you are saying. Im sorry but I just can't think how to implement it.

So is my class part right or am i really missing something?

and when i call the exception in the function.

would I do something like

NonExistent... < arghh idk >

I dont want you to just hand me an answer but can you give a example related more to my code?

Out of your current exception class, you can keep the word "class". Everything else is not even remotely related to what needs to be there -- the name of the class is Nonexistent, so call it that. There is no data inside it, so don't put anything in there. When you need to throw something, create an object of the Nonexistent class and throw it.

Originally Posted by tabstop

Out of your current exception class, you can keep the word "class". Everything else is not even remotely related to what needs to be there -- the name of the class is Nonexistent, so call it that. There is no data inside it, so don't put anything in there. When you need to throw something, create an object of the Nonexistent class and throw it.

wow idk why but that sorta helped
so

Code:

class NonExistent
{

};

NonExistent myexception()
{
throw 1;
}

Is this along the right lines?

or do i need something else

Originally Posted by bleuz

wow idk why but that sorta helped
so

Code:

class NonExistent
{

};

NonExistent myexception()
{
throw 1;
}

Is this along the right lines?

or do i need something else

You're up to 50%. The first four lines make sense. The last four lines do not. Where in the name of all that is good do you get the idea that a function is in any way, shape, or form involved in this process?

Oooo. or do i need something like

Code:

head.h

class NonExistent
{
};
...
...
...
main.cpp

if ( x = 1 )
     throw 2;
catch (NonExistent 2)
     cout << "error";

So you keep saying you've read something about exceptions. At this point I am forced to say I do not believe you.

You need to throw an object of type Nonexistent, when you get to all those points in somebody's-but-let's-call-it-your code that say //throw exception. That is all there is for you to do. It is not your job to do any catching. Look at the main code! Do you not see all those try/catch blocks?

Originally Posted by tabstop

So you keep saying you've read something about exceptions. At this point I am forced to say I do not believe you.

You need to throw an object of type Nonexistent, when you get to all those points in somebody's-but-let's-call-it-your code that say //throw exception. That is all there is for you to do. It is not your job to do any catching. Look at the main code! Do you not see all those try/catch blocks?

Everything I read was much more complex and I over-analyzed it. I knew I didn't need to catch it. I guess I was expecting to have to do more for it from what I read.

I appreciate all of your assistance and hopefully in the future it will all make sense.

You need to create a type, that you want to throw and later catch. In the catch block, you declare a variable of that type so you can access the element, that has been thrown. For example:

Code:

#include <iostream>
#include <string>

class SomethingFailedException
{
private:
	std::string desc;

public:
	SomethingFailedException( const std::string& description )
	{
		desc = description;
	}

	std::string GetDescription() const
	{
		return desc;
	}
};

void FunctionThatFailsAndThrows()
{
	throw SomethingFailedException("Oh no, the function failed!");
}

int main()
{
	try
	{
		FunctionThatFailsAndThrows();
	}
	catch( SomethingFailedException ex )
	{
		std::cout << "Something failed: " << ex.GetDescription() << std::endl;
	}

	return 0;
}

You don't need anything in your exception class unless you want the exception to be able to contain a message or some other data that might be useful in explaining why the exception was thrown.
I usually just derive my own exceptions from std::exception and leave it at that.