help with exception class

[dinks]

Hi,
I'm new to C++ and have been assigned a task which i dont completely
understand. Any help would be greately appreciated.

Here is the problem:
The class "linkedListType" use the "assert" facility. I am to get rid
of them and replace them with exceptions. I need to create a
"linkedListException" class that's declared and implemented in my
"linkedListType" class. This class needs to inherit from the base
"exception" class and return an error code (courtesy of a member
function of the "linkedListException" class). I don't understand
exceptions at all so i dont even know how to begin.

Here is the code for the "linkedListType" class (on the long side so
just copy and paste into your compiler):

/*--------------------- begin linkedList.h ------------------------*/

#ifndef H_LinkedListType
#define H_LinkedListType

#include <iostream>
#include <cassert>
using namespace std;

template <class Type>
struct nodeType
{
Type info;
nodeType<Type> *link;
};

template<class Type>
class linkedListType
{
friend ostream& operator<< <Type> (ostream&, const
linkedListType<Type>&);

public:
const linkedListType<Type>& operator=
(const linkedListType<Type>&);
//Overload the assignment operator.
void initializeList();
//Initializes the list to an empty state.
//Postcondition: first = NULL, last = NULL,
// count = 0
bool isEmptyList();
//Function to determine whether the list is empty.
//Postcondition: Returns true if the list is empty;
// otherwise, returns false.

int length();
//Function to return the number of nodes in the
//list.
//Postcondition: The value of count is returned.
void destroyList();
//Function to delete all the nodes from the list.
//Postcondition: first = NULL, last = NULL,
// count = 0
Type front();
//Function to return the first element of the list.
//Precondition: The list must exist and must not be
//empty.
//Postcondition: If the list is empty, then the
// program terminates; otherwise,
// the first element of the list is
// returned.
Type back();
//Function to return the last element of the
//list.
//Precondition: The list must exist and must not
//be empty.
//Postcondition: If the list is empty, then the
// program terminates; otherwise,
// the last element of the list is
// returned.

bool search(const Type& searchItem);
//Function to determine whether searchItem is in
//the list.
//Postcondition: Returns true if searchItem is found
// in the list; otherwise, it returns
// false.

void insertFirst(const Type& newItem);
//Function to insert newItem in the list.
//Postcondition: first points to the new list
// and newItem is inserted at the
// beginning of the list.

void insertLast(const Type& newItem);
//Function to return newItem at the end of the
//list.
//Postcondition: first points to the new list,
// newItem is inserted at the end
// of the list, and last points to
// the last node in the list.

void deleteNode(const Type& deleteItem);
//Function to delete deleteItem from the list.
//Postcondition: If found, the node containing
// deleteItem is deleted from the
// list, first points to the first
// node, and last points to the last
// node of the updated list.

linkedListType();
//default constructor
//Initializes the list to an empty state.
//Postcondition: first = NULL, last = NULL,
// count = 0

linkedListType(const linkedListType<Type>& otherList);
//copy constructor

~linkedListType();
//destructor
//Deletes all the nodes from the list.
//Postcondition: The list object is destroyed.

protected:
int count; //variable to store the number of
//elements in the list
nodeType<Type> *first; //pointer to the first node of
//the list
nodeType<Type> *last; //pointer to the last node of
//the list
private:
void copyList(const linkedListType<Type>& otherList);
//Function to make a copy of otherList.
//Postcondition: A copy of otherList is created
// and assigned to this list.
};

template<class Type>
bool linkedListType<Type>::isEmptyList()
{
return(first == NULL);
}

template<class Type>
linkedListType<Type>::linkedListType() // default constructor
{
first = NULL;
last = NULL;
count = 0;
}

template<class Type>
void linkedListType<Type>::destroyList()
{
nodeType<Type> *temp; //pointer to deallocate the memory
//occupied by the node
while(first != NULL) //while there are nodes in the list
{
temp = first; //set temp to the current node
first = first->link; //advance first to the next node
delete temp; //deallocate memory occupied by temp
}

last = NULL; //initialize last to NULL; first has already
//been set to NULL by the while loop
count = 0;
}


template<class Type>
void linkedListType<Type>::initializeList()
{
destroyList(); //if the list has any nodes, delete them
}

template<class Type>
int linkedListType<Type>::length()
{
return count;
} // end length

template<class Type>
Type linkedListType<Type>::front()
{
assert(first != NULL);
return first->info; //return the info of the first node
}//end front


template<class Type>
Type linkedListType<Type>::back()
{
assert(last != NULL);
return last->info; //return the info of the first node
}//end back

template<class Type>
bool linkedListType<Type>::search(const Type& searchItem)
{
nodeType<Type> *current; //pointer to traverse the list
bool found;

current = first; //set current to point to the
//first node in the list
found = false; //set found to false

while(current != NULL && !found) //search the list
if(current->info == searchItem) //the item is found
found = true;
else
current = current->link; //make current point
//to the next node

return found;
}//end search

template<class Type>
void linkedListType<Type>::insertFirst(const Type& newItem)
{
nodeType<Type> *newNode; //pointer to create the new node

newNode = new nodeType<Type>; //create the new node

assert(newNode != NULL); //If unable to allocate memory,
//terminate the program

newNode->info = newItem; //store the new item in the node
newNode->link = first; //insert newNode before first
first = newNode; //make first point to the
//actual first node
count++; //increment count

if(last == NULL) //if the list was empty, newNode is also
//the last node in the list
last = newNode;
}

template<class Type>
void linkedListType<Type>::insertLast(const Type& newItem)
{
nodeType<Type> *newNode; //pointer to create the new node

newNode = new nodeType<Type>; //create the new node

assert(newNode != NULL); //If unable to allocate memory,
//terminate the program

newNode->info = newItem; //store the new item in the node
newNode->link = NULL; //set the link field of newNode
//to NULL

if(first == NULL) //if the list is empty, newNode is
//both the first and last node
{
first = newNode;
last = newNode;
count++; //increment count
}
else //the list is not empty, insert newNode after last
{
last->link = newNode; //insert newNode after last
last = newNode; //make last point to the actual last node
count++; //increment count
}
}//end insertLast

template<class Type>
void linkedListType<Type>::deleteNode(const Type& deleteItem)
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent; //pointer just before current
bool found;

if(first == NULL) //Case 1; list is empty.
cerr<<"Can not delete from an empty list.\n";
else
{
if(first->info == deleteItem) //Case 2
{
current = first;
first = first->link;
count--;
if(first == NULL) //list has only one node
last = NULL;
delete current;
}
else //search the list for the node with the given info
{
found = false;
trailCurrent = first; //set trailCurrent to point to
//the first node
current = first->link; //set current to point to the
//second node

while(current != NULL && !found)
{
if(current->info != deleteItem)
{
trailCurrent = current;
current = current->link;
}
else
found = true;
} // end while

if(found) //Case 3; if found, delete the node
{
trailCurrent->link = current->link;
count--;

if(last == current) //node to be deleted was
//the last node
last = trailCurrent; //update the value of last

delete current; //delete the node from the list
}
else
cout<<"Item to be deleted is not in the list."<<endl;
} //end else
} //end else
} //end deleteNode


//Overloading the stream insertion operator
template<class Type>
ostream& operator<<(ostream& osObject, const linkedListType<Type>&
list)
{
nodeType<Type> *current; //pointer to traverse the list

current = list.first; //set current so that it points to
//the first node
while(current != NULL) //while more data to print
{
osObject<<current->info<<" ";
current = current->link;
}

return osObject;
}

template<class Type>
linkedListType<Type>::~linkedListType() // destructor
{
destroyList();
}//end destructor


template<class Type>
void linkedListType<Type>::copyList
(const linkedListType<Type>& otherList)
{
nodeType<Type> *newNode; //pointer to create a node
nodeType<Type> *current; //pointer to traverse the list

if(first != NULL) //if the list is nonempty, make it empty
destroyList();

if(otherList.first == NULL) //otherList is empty
{
first = NULL;
last = NULL;
count = 0;
}
else
{
current = otherList.first; //current points to the
//list to be copied
count = otherList.count;

//copy the first node
first = new nodeType<Type>; //create the node

assert(first != NULL);

first->info = current->info; //copy the info
first->link = NULL; //set the link field of
//the node to NULL
last = first; //make last point to the
//first node
current = current->link; //make current point to
//the next node

//copy the remaining list
while(current != NULL)
{
newNode = new nodeType<Type>; //create a node

assert(newNode!= NULL);

newNode->info = current->info; //copy the info
newNode->link = NULL; //set the link of
//newNode to NULL
last->link = newNode; //attach newNode after last
last = newNode; //make last point to
//the actual last node
current = current->link; //make current point to
//the next node
}//end while
}//end else
}//end copyList


//copy constructor
template<class Type>
linkedListType<Type>::linkedListType
(const linkedListType<Type>& otherList)
{
first = NULL;

copyList(otherList);

}//end copy constructor

//overload the assignment operator
template<class Type>
const linkedListType<Type>& linkedListType<Type>:perator=
(const linkedListType<Type>& otherList)
{
if(this != &otherList) //avoid self-copy
copyList(otherList);

return *this;
}

#endif

 

[Peter Koch Larsen]

Hi,
I'm new to C++ and have been assigned a task which i dont completely
understand. Any help would be greately appreciated.

Here is the problem:
The class "linkedListType" use the "assert" facility. I am to get rid
of them and replace them with exceptions.

Never do that. Assert is to check program sanity, exceptions for coping with
exceptional but expected exceptions.

I need to create a
"linkedListException" class that's declared and implemented in my
"linkedListType" class. This class needs to inherit from the base
"exception" class and return an error code (courtesy of a member
function of the "linkedListException" class). I don't understand
exceptions at all so i dont even know how to begin.

Whoever gave you that assignment knew nothing about exceptions.

 

[John Harrison]

Hi,
I'm new to C++ and have been assigned a task which i dont completely
understand. Any help would be greately appreciated.

Here is the problem:
The class "linkedListType" use the "assert" facility. I am to get rid
of them and replace them with exceptions. I need to create a
"linkedListException" class that's declared and implemented in my
"linkedListType" class. This class needs to inherit from the base
"exception" class and return an error code (courtesy of a member
function of the "linkedListException" class). I don't understand
exceptions at all so i dont even know how to begin.

Well do you need to understand exceptions to do this exercise?

You are to find the assert and replace them with exception throws. I.e.

assert(something);

becomes

if (!something)
throw linkedListException(...);

linkedListException is just a class like any other. You are told a few
things about it. It must derive from exception (I presume that's
std::exception declared in the <exception> header file) and it must have a
method that returns an error code, presumably the error code is supplied as
an argument to the linkedListException constructor, i.e. it goes where I put
.... above.

john