Search Results for “linked list”

Search Results for: linked list

C# || Remove Linked List Elements – How To Remove All Target Linked List Elements Using C#

April 02, 2022 admin No comments

The following is a module with functions which demonstrates how to remove all target linked list elements using C#.

1. Remove Elements – Problem Statement

Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

Example 1:

Input: head = [1,2,6,3,4,5,6], val = 6 Output: [1,2,3,4,5]

Example 2:

Input: head = [], val = 1 Output: []

Example 3:

Input: head = [7,7,7,7], val = 7 Output: []

2. Remove Elements – Solution

The following is a solution which demonstrates how to remove all target linked list elements.



		
		
			2. Remove Elements - Solution
			
C#
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Apr 2, 2022
//    Taken From: http://programmingnotes.org/
//    File:  Solution.cs
//    Description: Demonstrates how to remove all target linked list elements
// ============================================================================
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode RemoveElements(ListNode head, int val) {
        var ptr = head;

        // Loop through data checking to see if the next node equals the target value
        while (ptr != null && ptr.next != null) {

            // If the next node value is the target value, set the next node
            // to point to the one after it
            if (ptr.next.val == val) {
                ptr.next = ptr.next.next;
            } else {
                // Advance to the next node
                ptr = ptr.next;
            }
        }

        // If the head equals the target value, advance to the next
        if (head != null && head.val == val) {
            head = head.next;
        }

        return head;
    }
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Apr 2, 2022
//    Taken From: http://programmingnotes.org/
//    File:  Solution.cs
//    Description: Demonstrates how to remove all target linked list elements
// ============================================================================
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode RemoveElements(ListNode head, int val) {
        var ptr = head;
 
        // Loop through data checking to see if the next node equals the target value
        while (ptr != null && ptr.next != null) {
 
            // If the next node value is the target value, set the next node
            // to point to the one after it
            if (ptr.next.val == val) {
                ptr.next = ptr.next.next;
            } else {
                // Advance to the next node
                ptr = ptr.next;
            }
        }
 
        // If the head equals the target value, advance to the next
        if (head != null && head.val == val) {
            head = head.next;
        }
 
        return head;
    }
}// http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output for the example cases:

[1,2,3,4,5] [] []

C# || How To Flatten A Multilevel Doubly Linked List Using C#

October 30, 2021 admin No comments

The following is a module with functions which demonstrates how to flatten a doubly linked list using C#.

1. Flatten – Problem Statement

You are given a doubly linked list which in addition to the next and previous pointers, it could have a child pointer, which may or may not point to a separate doubly linked list. These child lists may have one or more children of their own, and so on, to produce a multilevel data structure, as shown in the example below.

Flatten the list so that all the nodes appear in a single-level, doubly linked list. You are given the head of the first level of the list.

Example 1:

Input: head = [1,2,3,4,5,6,null,null,null,7,8,9,10,null,null,11,12] Output: [1,2,3,7,8,11,12,9,10,4,5,6] Explanation:
The multilevel linked list in the input is as follows:

After flattening the multilevel linked list it becomes:

Example 2:

Input: head = [1,2,null,3] Output: [1,3,2] Explanation:
The input multilevel linked list is as follows:
1---2---NULL | 3---NULL

Example 3:

Input: head = [] Output: []

2. Flatten – Solution

The following are two solutions which demonstrates how to flatten a doubly linked list.

Iterative



		
		
			2. Flatten Iterative - Solution
			
C#
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Oct 30, 2021
//    Taken From: http://programmingnotes.org/
//    File:  Solution.cs
//    Description: Demonstrates how to flatten a doubly linked list
// ============================================================================
/*
// Definition for a Node.
public class Node {
    public int val;
    public Node prev;
    public Node next;
    public Node child;
}
*/
public class Solution {
    public Node Flatten(Node head) {
        var current = head;
        var stack = new Stack<Node>();

        // Loop through nodes
        while (current != null) {

            // Check to see if node has child
            if (current.child != null) {
                // If current node has a next node, save to stack
                // so we can reconnect it to the tail
                // of the child node later
                if (current.next != null) {
                    stack.Push(current.next);
                }

                // Set the next node as the child,
                // we will now iterate down this path
                current.next = current.child;

                // Set the previous node as the current
                current.next.prev = current;

                // Set child to null
                current.child = null;

            } else if (current.next == null) {
                // Reconnect node at the top of the
                // stack to the tail child node
                if (stack.Count > 0) {
                    // Set the next node as the reconnected node,
                    // we will now iterate down this path
                    current.next = stack.Pop();
                    current.next.prev = current;
                }
            }
            current = current.next;
        }

        return head;
    }
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Oct 30, 2021
//    Taken From: http://programmingnotes.org/
//    File:  Solution.cs
//    Description: Demonstrates how to flatten a doubly linked list
// ============================================================================
/*
// Definition for a Node.
public class Node {
    public int val;
    public Node prev;
    public Node next;
    public Node child;
}
*/
public class Solution {
    public Node Flatten(Node head) {
        var current = head;
        var stack = new Stack<Node>();
 
        // Loop through nodes
        while (current != null) {
 
            // Check to see if node has child
            if (current.child != null) {
                // If current node has a next node, save to stack
                // so we can reconnect it to the tail
                // of the child node later
                if (current.next != null) {
                    stack.Push(current.next);
                }
 
                // Set the next node as the child,
                // we will now iterate down this path
                current.next = current.child;
 
                // Set the previous node as the current
                current.next.prev = current;
 
                // Set child to null
                current.child = null;
 
            } else if (current.next == null) {
                // Reconnect node at the top of the
                // stack to the tail child node
                if (stack.Count > 0) {
                    // Set the next node as the reconnected node,
                    // we will now iterate down this path
                    current.next = stack.Pop();
                    current.next.prev = current;
                }
            }
            current = current.next;
        }
 
        return head;
    }
}// http://programmingnotes.org/

Recursive



		
		
			2. Flatten Recursive - Solution
			
C#
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Oct 30, 2021
//    Taken From: http://programmingnotes.org/
//    File:  Solution.cs
//    Description: Demonstrates how to flatten a doubly linked list
// ============================================================================
/*
// Definition for a Node.
public class Node {
    public int val;
    public Node prev;
    public Node next;
    public Node child;
}
*/
public class Solution {
    public Node Flatten(Node head) {
        Flatten(head, null);
        return head;
    }

    private Node Flatten(Node current, Node previous) {
        if (current == null) {
            return previous;
        }

        // If previous node exists, set the next and previous values
        if (previous != null) {
            previous.next = current;
            current.prev = previous;
        }

        // Save the next node so we can reconnect it to the tail
        // of the child node later
        var next = current.next;

        // Traverse down child path.
        // If children exist, this returns the last child for the current node
        var tail = Flatten(current.child, current);

        // Child path has been explored, set to null
        current.child = null;

        // Reconnect the next node to the tail child node
        return Flatten(next, tail);
    }
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Oct 30, 2021
//    Taken From: http://programmingnotes.org/
//    File:  Solution.cs
//    Description: Demonstrates how to flatten a doubly linked list
// ============================================================================
/*
// Definition for a Node.
public class Node {
    public int val;
    public Node prev;
    public Node next;
    public Node child;
}
*/
public class Solution {
    public Node Flatten(Node head) {
        Flatten(head, null);
        return head;
    }
 
    private Node Flatten(Node current, Node previous) {
        if (current == null) {
            return previous;
        }
 
        // If previous node exists, set the next and previous values
        if (previous != null) {
            previous.next = current;
            current.prev = previous;
        }
 
        // Save the next node so we can reconnect it to the tail
        // of the child node later
        var next = current.next;
 
        // Traverse down child path.
        // If children exist, this returns the last child for the current node
        var tail = Flatten(current.child, current);
 
        // Child path has been explored, set to null
        current.child = null;
 
        // Reconnect the next node to the tail child node
        return Flatten(next, tail);
    }
}// http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output for the example cases:

[1,2,3,7,8,11,12,9,10,4,5,6] [1,3,2] []

C++ || Snippet – Simple Linked List Using Delete, Insert, & Display Functions

August 18, 2012 admin No comments

The following is sample code for a simple linked list, which implements the following functions: “Delete, Insert, and Display.”

The sample code provided on this page is a stripped down version of a more robust linked list class which was previously discussed on this site. Sample code for that can be found here.

It is recommended you check that out as the functions implemented within that class are very useful.



		
		
			Simple Linked List
			
C++
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Aug 18, 2012
//    Taken From: http://programmingnotes.org/
//    File:  SimpleList.cpp
//    Description: Demonstrates the use of a simple linked list.
// ============================================================================
#include <iostream>
#include <string>
using namespace std;

struct node
{
    /* -- you can use different data types here
         -- instead of just a string
    char letter;
    int number;
    double fNumber;
    */
    string name;
    node* next;
};

// global variables
// this is the front of the list
node* head = NULL;

// function prototype
void Insert(string info);
void Delete(string info);
void Display();
void DestroyList();

int main()
{
    // if you want to insert data into the list
    // this is one way you can do it, using a 'temp' pointer
    node* temp = new node;
    temp->name = "My Programming Notes";
    temp->next = NULL;

    // set the head node to the data thats in the 'temp' pointer
    head = temp;

    // display data to the screen
    cout << head->name <<endl<<endl;

    // use the insert function to add new data to the list
    // NOTE: you could have also used the 'insert' function ^ above
    // to place data into the list
    Insert("Is An Awesome Site!");

    // insert more data into the list
    Insert("August");
    Display();

    // delete the selected text from the list
    Delete("August");
    Display();

    // destroy the current pointers in the list
    // after you are finished using them
    DestroyList();

    return 0;
}// end of main

void Insert(string info)
{
    node* newItem = new node;
    newItem->name = info;
    newItem->next = NULL;

    // if the list is empty, add new item to the front
    if(head == NULL)
    {
        head = newItem;
    }
    else // if the list isnt empty, add new item to the end
    {
        node* iter = head;
        while(iter->next != NULL)
        {
            iter = iter->next;
        }
        iter->next = newItem;
    }
}// end of Insert

void Delete(string info)
{
    node* iter = head;

    // if the list is empty, do nothing
    if(head == NULL)
    {
        return;
    }
    // delete the first item in the list
    else if(head->name == info)
    {
        head = head->next;
        delete iter;
    }
    // search the list until we find the desired item
    else
    {
        while(iter->next != NULL)
        {
            if(iter->next->name == info)
            {
                node* deleteNode = iter->next;
                iter->next = iter->next->next;
                delete deleteNode;
                break;
            }
            iter = iter->next;
        }
    }
}// end of Delete

void Display()
{
    node* iter = head;
    // traverse thru the list, displaying the
    // text at each node location
    while(iter != NULL)
    {
        cout<<iter->name<<endl;
        iter = iter->next;
    }
    cout<<endl;
}// end of Display

void DestroyList()
{
    if(head != NULL)
    {
        cout << "\n\nDestroying nodes...\n";
        while(head != NULL)
        {
            node* temp = head;
            cout << temp->name <<endl;
            head = head->next;
            delete temp;
        }
    }
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Aug 18, 2012
//    Taken From: http://programmingnotes.org/
//    File:  SimpleList.cpp
//    Description: Demonstrates the use of a simple linked list.
// ============================================================================
#include <iostream>
#include <string>
using namespace std;
 
struct node
{
    /* -- you can use different data types here
         -- instead of just a string
    char letter;
    int number;
    double fNumber;
    */
    string name;
    node* next;
};
 
// global variables
// this is the front of the list
node* head = NULL;
 
// function prototype
void Insert(string info);
void Delete(string info);
void Display();
void DestroyList();
 
int main()
{
    // if you want to insert data into the list
    // this is one way you can do it, using a 'temp' pointer
    node* temp = new node;
    temp->name = "My Programming Notes";
    temp->next = NULL;
 
    // set the head node to the data thats in the 'temp' pointer
    head = temp;
 
    // display data to the screen
    cout << head->name <<endl<<endl;
 
    // use the insert function to add new data to the list
    // NOTE: you could have also used the 'insert' function ^ above
    // to place data into the list
    Insert("Is An Awesome Site!");
 
    // insert more data into the list
    Insert("August");
    Display();
 
    // delete the selected text from the list
    Delete("August");
    Display();
 
    // destroy the current pointers in the list
    // after you are finished using them
    DestroyList();
 
    return 0;
}// end of main
 
void Insert(string info)
{
    node* newItem = new node;
    newItem->name = info;
    newItem->next = NULL;
 
    // if the list is empty, add new item to the front
    if(head == NULL)
    {
        head = newItem;
    }
    else // if the list isnt empty, add new item to the end
    {
        node* iter = head;
        while(iter->next != NULL)
        {
            iter = iter->next;
        }
        iter->next = newItem;
    }
}// end of Insert
 
void Delete(string info)
{
    node* iter = head;
 
    // if the list is empty, do nothing
    if(head == NULL)
    {
        return;
    }
    // delete the first item in the list
    else if(head->name == info)
    {
        head = head->next;
        delete iter;
    }
    // search the list until we find the desired item
    else
    {
        while(iter->next != NULL)
        {
            if(iter->next->name == info)
            {
                node* deleteNode = iter->next;
                iter->next = iter->next->next;
                delete deleteNode;
                break;
            }
            iter = iter->next;
        }
    }
}// end of Delete
 
void Display()
{
    node* iter = head;
    // traverse thru the list, displaying the
    // text at each node location
    while(iter != NULL)
    {
        cout<<iter->name<<endl;
        iter = iter->next;
    }
    cout<<endl;
}// end of Display
 
void DestroyList()
{
    if(head != NULL)
    {
        cout << "\n\nDestroying nodes...\n";
        while(head != NULL)
        {
            node* temp = head;
            cout << temp->name <<endl;
            head = head->next;
            delete temp;
        }
    }
}// http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output

My Programming Notes
My Programming Notes Is An Awesome Site! August [DELETE THE TEXT "AUGUST"] My Programming Notes Is An Awesome Site!
Destroying nodes... My Programming Notes Is An Awesome Site!

C++ || Snippet – Custom Template Linked List Sample Code

July 26, 2012 admin 1 Comment

This page will consist of sample code for a singly linked list, which is loosely based on the built in C++ “List” library. Provided in the linked list class are the following functions:



		
		
			* PushFront - Adds new item to the front of the list (LIFO)

* PushBack - Adds new item to the back of the list (FIFO)

* PopFront - Returns & removes first item from the list

* PopBack - Returns & removes last item from the list

* Front - Returns (but does not delete) the first item from the list

* Back - Returns (but does not delete) the last item from the list

* Delete - Searches and deletes the requested item

* Display - Display all the current contents in the list

* Replace - Replaces existing item from the list with a new item
            If existing item cannot be found, the new item is added to the back of the list

* InsertBefore - Inserts new item before the existing item. 
                If existing item cannot be found, the new item is added to the back of the list

* InsertAfter - Inserts new item after the existing item. 
                If existing item cannot be found, the new item is added to the back of the list

* InsertInOrder - Inserts new item in numerical order, from lowest to highest

* Size - Return the current size of the list

* MakeEmpty - Initializes the list to an empty state 
			
				
					
				
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						* PushFront - Adds new item to the front of the list (LIFO)
 
* PushBack - Adds new item to the back of the list (FIFO)
 
* PopFront - Returns & removes first item from the list
 
* PopBack - Returns & removes last item from the list
 
* Front - Returns (but does not delete) the first item from the list
 
* Back - Returns (but does not delete) the last item from the list
 
* Delete - Searches and deletes the requested item
 
* Display - Display all the current contents in the list
 
* Replace - Replaces existing item from the list with a new item
            If existing item cannot be found, the new item is added to the back of the list
 
* InsertBefore - Inserts new item before the existing item. 
                If existing item cannot be found, the new item is added to the back of the list
 
* InsertAfter - Inserts new item after the existing item. 
                If existing item cannot be found, the new item is added to the back of the list
 
* InsertInOrder - Inserts new item in numerical order, from lowest to highest
 
* Size - Return the current size of the list
 
* MakeEmpty - Initializes the list to an empty state

From the following, the functions of interest to look out for are the “Delete, Display, Replace, InsertBefore, InsertAfter, and InsertInOrder” functions as they are typically used as programming assignments in many C++ Data structures courses to further demonstrate how linked lists operate.



		
		
			#include 'LinkedList.h'
			
C++
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Jul 26, 2012
//    Taken From: http://programmingnotes.org/
//    File:  LinkedList.h
//    Description: This is a class which implements various functions which
//          demonstrates the use of a Linked List. 
// ============================================================================
#include <iostream>

template <class ItemType>
class LinkedList
{
public:
    LinkedList();
        /*   Function: Constructor initializes list 
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty();
        /*   Function: Determines whether queue is empty
            Precondition: List has been created
            Postcondition: The function = true if the list is empty and the
                             function = false if list is not empty */
    void PushFront(ItemType item);
        /*   Function: Adds new item to the front of the list (LIFO)
            Precondition:  List has been created and is not full
            Postcondition: Item is in the list */
    void PushBack(ItemType item);
        /*   Function: Adds new item to the back of the list (FIFO)
            Precondition:  List has been created and is not full
            Postcondition: Item is in the list */
    ItemType PopFront();
        /*   Function: Returns & removes first item from the last
            Precondition: List has been initialized
            Postcondition: The first item in the list is removed */
    ItemType PopBack();
        /*   Function: Returns & removes last item from the list
            Precondition: List has been initialized
            Postcondition: The last item in the list is removed */
    ItemType Front();
        /*   Function: Returns (but does not delete) the first item from the list
            Precondition: List has been initialized
            Postcondition: The first item in the list is removed */
    ItemType Back();
        /*   Function: Returns (but does not delete) the last item from the list
            Precondition: List has been initialized
            Postcondition: The last item in the list is removed */
    void Delete(ItemType item);
        /*   Function: Searches and deletes the requested item
            Precondition:  List has been created and is not empty
            Postcondition: Item removed from the list */
    void Display();
        /*   Function: Display all the current contents in the list
            Precondition:  List has been created and is not empty
            Postcondition: List is displayed to the screen */
    void Replace(ItemType initial, ItemType replace);
        /*   Function: Replaces existing item from the list with a new item
            Precondition:  List has been created and is not empty
            Postcondition: Initial item is replaced with the new one */
    void InsertBefore(ItemType initial, ItemType newItem);
        /*   Function: Inserts new item before the existing item
            Precondition:  List has been created and is not empty
            Postcondition: New item is inserted before the existing item */
    void InsertAfter(ItemType initial, ItemType newItem);
        /*   Function: Inserts new item after the existing item
            Precondition:  List has been created and is not empty
            Postcondition: New item is inserted after the existing item */
    void InsertInOrder(ItemType item);  
        /*   Function: Inserts new item in numerical order, from lowest to highest
            Precondition:  List has been created and is not empty
            Postcondition: The list is sorted in numerical order */
    int Size();
        /*   Function: Return the current size of the list
            Precondition: List has been initialized
            Postcondition: The size of the list is returned */
    void MakeEmpty();
        /*   Function: Initializes the list to an empty state 
            Precondition: List has been created
            Postcondition: List no longer exists */
    ~LinkedList();
        /*   Function: Deletes all the items in the list
            Precondition: List has been declared
            Postcondition: List no longer exists */

private:
    struct node
    {
        ItemType info;
        node* next;
    };
    node* head; 
    int size;
};

//=========================  Implementation  ================================//

template <class ItemType>
LinkedList<ItemType>::LinkedList()
{
    head = NULL;
    size = 0;
}// end of LinkedList

template <class ItemType>
bool LinkedList<ItemType>::IsEmpty()
{
    return (head==NULL);
}// end of IsEmpty

template <class ItemType>
void LinkedList<ItemType>::PushFront(ItemType item)
{
    // LIFO 
    node* temp = new node;
    temp-> info = item;
    temp-> next = head;
    head = temp;
    ++size;
}// end of PushFront

template <class ItemType>
void LinkedList<ItemType>::PushBack(ItemType item)
{
    // FIFO
    node* temp = new node;
    temp->info = item;
    temp->next = NULL;
    
    if(IsEmpty())
    {
        head=temp;
    }
    else
    {
        node* temp2 = head;        
        while(temp2->next!=NULL)
        {
            temp2=temp2->next;
        }
        temp2->next=temp;
    }
    ++size;
}// end of PushBack

template <class ItemType>
ItemType LinkedList<ItemType>::PopFront()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else
    {  
        ItemType item = head-> info;  
        node* temp = head;
        head = head-> next;
        delete temp;
        --size;
        return item;
    }
}// end of PopFront

template <class ItemType>
ItemType LinkedList<ItemType>::PopBack()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else if(size == 1)
    {
        ItemType item = PopFront();
        return item;
    }
    else
    {
        node* temp = head;
        ItemType item;
        while(temp->next != NULL)
        {
            if(temp->next->next==NULL)
            {
                node* temp2=temp->next;
                temp->next=temp->next->next;
                item = temp2-> info;
                delete temp2;
                break;
            }
            temp=temp->next;
        }
        --size;
        return item;
    }   
}// end of PopBack

template <class ItemType>
ItemType LinkedList<ItemType>::Front()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else
    { 
        return head-> info;
    }
}// end of Front

template <class ItemType>
ItemType LinkedList<ItemType>::Back() 
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else
    {
        node* temp = head; 
        while(temp->next != NULL)
        {
            temp = temp-> next;
        }
        ItemType item = temp-> info;
        return item;
    }   
}// end of Back

template <class ItemType>
void LinkedList<ItemType>::Delete(ItemType item)
{
    node* temp=head;
    if(IsEmpty())
    {
        return;
    }
    else if(temp->info==item)
    {
        head=head->next;
        delete temp;
        --size;
    }
    else
    {
        while(temp->next!=NULL)
        {
            if(temp->next->info==item)
            {
                node* temp2=temp->next;
                temp->next=temp->next->next;
                delete temp2;
                --size;
                break;
            }
            temp=temp->next;
        }
    }
}// end of Delete

template <class ItemType>
void LinkedList<ItemType>::Display()
{
    node* temp=head;
    while(temp!=NULL)
    {
        std::cout<<temp->info<<std::endl;
        temp=temp->next;
    }
}// end of Display

template <class ItemType>
void LinkedList<ItemType>::Replace(ItemType initial, ItemType replace)
{
    node* temp=head;
    if(IsEmpty())
    {
        PushFront(replace);
    }
    else if(temp->info==initial)
    {
        temp->info=replace;
    }
    else
    {        
        while(temp->next!=NULL)
        {
            if(temp->info==initial)
            {
                temp->info=replace;
                break;
            }
            temp=temp->next;
        }
        if(temp->next==NULL)
        {
            PushBack(replace);
        }
    }
}// end of Replace

template <class ItemType>
void LinkedList<ItemType>::InsertBefore(ItemType initial, ItemType newItem)
{
    node* temp=head;
    node* temp2=new node;
    temp2->info=initial;
    temp2->next=NULL;     
    
    if(IsEmpty())
    {
        PushFront(newItem);
    }
    else if(temp->info==initial)
    {
        temp->info=newItem; 
        temp2->next=temp->next;
        temp->next=temp2;
        ++size;
    }
    else
    {
        while(temp->next!=NULL)
        {
            if(temp->info==initial)
            {
                temp->info=newItem; 
                temp2->next=temp->next;
                temp->next=temp2;
                ++size;
                break;
            }
            temp=temp->next;           
        }
        if(temp->next==NULL)
        {
            PushBack(newItem);
        }
    }
}// end of InsertBefore

template <class ItemType>
void LinkedList<ItemType>::InsertAfter(ItemType initial, ItemType newItem)
{
    node* temp=head;
    node* temp2=new node;
    temp2->info=newItem;
    temp2->next=NULL;
    
    if(IsEmpty())
    {
        PushFront(newItem);
    }
    else if(temp->info==initial)
    {
        temp2->next=temp->next;
        temp->next=temp2;
        ++size;
    }
    else
    {   
        while(temp->next!=NULL)
        {
            if(temp->info==initial)
            {
                temp2->next=temp->next;
                temp->next=temp2;
                ++size;
                break;
            }
            temp=temp->next;
        }
        if(temp->next==NULL)
        {
            PushBack(newItem);
        }
    }
}// end of InsertAfter

template <class ItemType>
void LinkedList<ItemType>::InsertInOrder(ItemType item)
{
    if(IsEmpty())
    {
        PushFront(item);
    }
    else
    {
        node* temp=head;
        node* temp2=new node;
    
        if(item <=(temp->info))
        {  
            ItemType placeHolder=temp->info;
            temp2->info=placeHolder;
            temp->info=item;
            temp2->next=temp->next;
            temp->next=temp2;
            ++size;
        } 
        else
        {
            while(temp->next!=NULL)
            {       
                if(((temp->info) <= item) && (item <= (temp->next->info)))
                {           
                    temp2->info=item;
                    temp2->next=temp->next;
                    temp->next=temp2;
                    ++size;
                    return;
                }
                temp=temp->next;
            }
            if(temp->next==NULL)
            {
                PushBack(item);
            }
        }
    }
}// end of InsertInOrder

template <class ItemType>
int LinkedList<ItemType>::Size()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    return size;
}// end of Size 

template <class ItemType>
void LinkedList<ItemType>::MakeEmpty()
{
    if(!IsEmpty())
    {
        std::cout << "\nDestroying nodes...\n";
        while(!IsEmpty())
        {
            node* temp = head;
            //std::cout << temp-> info << '\n';
            head = head-> next;
            delete temp;
        }
        size = 0;
    }
}// end of MakeEmpty

template <class ItemType>
LinkedList<ItemType>::~LinkedList()
{
    MakeEmpty();
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   Jul 26, 2012
//    Taken From: http://programmingnotes.org/
//    File:  LinkedList.h
//    Description: This is a class which implements various functions which
//          demonstrates the use of a Linked List. 
// ============================================================================
#include <iostream>
 
template <class ItemType>
class LinkedList
{
public:
    LinkedList();
        /*   Function: Constructor initializes list 
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty();
        /*   Function: Determines whether queue is empty
            Precondition: List has been created
            Postcondition: The function = true if the list is empty and the
                             function = false if list is not empty */
    void PushFront(ItemType item);
        /*   Function: Adds new item to the front of the list (LIFO)
            Precondition:  List has been created and is not full
            Postcondition: Item is in the list */
    void PushBack(ItemType item);
        /*   Function: Adds new item to the back of the list (FIFO)
            Precondition:  List has been created and is not full
            Postcondition: Item is in the list */
    ItemType PopFront();
        /*   Function: Returns & removes first item from the last
            Precondition: List has been initialized
            Postcondition: The first item in the list is removed */
    ItemType PopBack();
        /*   Function: Returns & removes last item from the list
            Precondition: List has been initialized
            Postcondition: The last item in the list is removed */
    ItemType Front();
        /*   Function: Returns (but does not delete) the first item from the list
            Precondition: List has been initialized
            Postcondition: The first item in the list is removed */
    ItemType Back();
        /*   Function: Returns (but does not delete) the last item from the list
            Precondition: List has been initialized
            Postcondition: The last item in the list is removed */
    void Delete(ItemType item);
        /*   Function: Searches and deletes the requested item
            Precondition:  List has been created and is not empty
            Postcondition: Item removed from the list */
    void Display();
        /*   Function: Display all the current contents in the list
            Precondition:  List has been created and is not empty
            Postcondition: List is displayed to the screen */
    void Replace(ItemType initial, ItemType replace);
        /*   Function: Replaces existing item from the list with a new item
            Precondition:  List has been created and is not empty
            Postcondition: Initial item is replaced with the new one */
    void InsertBefore(ItemType initial, ItemType newItem);
        /*   Function: Inserts new item before the existing item
            Precondition:  List has been created and is not empty
            Postcondition: New item is inserted before the existing item */
    void InsertAfter(ItemType initial, ItemType newItem);
        /*   Function: Inserts new item after the existing item
            Precondition:  List has been created and is not empty
            Postcondition: New item is inserted after the existing item */
    void InsertInOrder(ItemType item);  
        /*   Function: Inserts new item in numerical order, from lowest to highest
            Precondition:  List has been created and is not empty
            Postcondition: The list is sorted in numerical order */
    int Size();
        /*   Function: Return the current size of the list
            Precondition: List has been initialized
            Postcondition: The size of the list is returned */
    void MakeEmpty();
        /*   Function: Initializes the list to an empty state 
            Precondition: List has been created
            Postcondition: List no longer exists */
    ~LinkedList();
        /*   Function: Deletes all the items in the list
            Precondition: List has been declared
            Postcondition: List no longer exists */
 
private:
    struct node
    {
        ItemType info;
        node* next;
    };
    node* head; 
    int size;
};
 
//=========================  Implementation  ================================//
 
template <class ItemType>
LinkedList<ItemType>::LinkedList()
{
    head = NULL;
    size = 0;
}// end of LinkedList
 
template <class ItemType>
bool LinkedList<ItemType>::IsEmpty()
{
    return (head==NULL);
}// end of IsEmpty
 
template <class ItemType>
void LinkedList<ItemType>::PushFront(ItemType item)
{
    // LIFO 
    node* temp = new node;
    temp-> info = item;
    temp-> next = head;
    head = temp;
    ++size;
}// end of PushFront
 
template <class ItemType>
void LinkedList<ItemType>::PushBack(ItemType item)
{
    // FIFO
    node* temp = new node;
    temp->info = item;
    temp->next = NULL;
    
    if(IsEmpty())
    {
        head=temp;
    }
    else
    {
        node* temp2 = head;        
        while(temp2->next!=NULL)
        {
            temp2=temp2->next;
        }
        temp2->next=temp;
    }
    ++size;
}// end of PushBack
 
template <class ItemType>
ItemType LinkedList<ItemType>::PopFront()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else
    {  
        ItemType item = head-> info;  
        node* temp = head;
        head = head-> next;
        delete temp;
        --size;
        return item;
    }
}// end of PopFront
 
template <class ItemType>
ItemType LinkedList<ItemType>::PopBack()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else if(size == 1)
    {
        ItemType item = PopFront();
        return item;
    }
    else
    {
        node* temp = head;
        ItemType item;
        while(temp->next != NULL)
        {
            if(temp->next->next==NULL)
            {
                node* temp2=temp->next;
                temp->next=temp->next->next;
                item = temp2-> info;
                delete temp2;
                break;
            }
            temp=temp->next;
        }
        --size;
        return item;
    }   
}// end of PopBack
 
template <class ItemType>
ItemType LinkedList<ItemType>::Front()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else
    { 
        return head-> info;
    }
}// end of Front
 
template <class ItemType>
ItemType LinkedList<ItemType>::Back() 
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    else
    {
        node* temp = head; 
        while(temp->next != NULL)
        {
            temp = temp-> next;
        }
        ItemType item = temp-> info;
        return item;
    }   
}// end of Back
 
template <class ItemType>
void LinkedList<ItemType>::Delete(ItemType item)
{
    node* temp=head;
    if(IsEmpty())
    {
        return;
    }
    else if(temp->info==item)
    {
        head=head->next;
        delete temp;
        --size;
    }
    else
    {
        while(temp->next!=NULL)
        {
            if(temp->next->info==item)
            {
                node* temp2=temp->next;
                temp->next=temp->next->next;
                delete temp2;
                --size;
                break;
            }
            temp=temp->next;
        }
    }
}// end of Delete
 
template <class ItemType>
void LinkedList<ItemType>::Display()
{
    node* temp=head;
    while(temp!=NULL)
    {
        std::cout<<temp->info<<std::endl;
        temp=temp->next;
    }
}// end of Display
 
template <class ItemType>
void LinkedList<ItemType>::Replace(ItemType initial, ItemType replace)
{
    node* temp=head;
    if(IsEmpty())
    {
        PushFront(replace);
    }
    else if(temp->info==initial)
    {
        temp->info=replace;
    }
    else
    {        
        while(temp->next!=NULL)
        {
            if(temp->info==initial)
            {
                temp->info=replace;
                break;
            }
            temp=temp->next;
        }
        if(temp->next==NULL)
        {
            PushBack(replace);
        }
    }
}// end of Replace
 
template <class ItemType>
void LinkedList<ItemType>::InsertBefore(ItemType initial, ItemType newItem)
{
    node* temp=head;
    node* temp2=new node;
    temp2->info=initial;
    temp2->next=NULL;     
    
    if(IsEmpty())
    {
        PushFront(newItem);
    }
    else if(temp->info==initial)
    {
        temp->info=newItem; 
        temp2->next=temp->next;
        temp->next=temp2;
        ++size;
    }
    else
    {
        while(temp->next!=NULL)
        {
            if(temp->info==initial)
            {
                temp->info=newItem; 
                temp2->next=temp->next;
                temp->next=temp2;
                ++size;
                break;
            }
            temp=temp->next;           
        }
        if(temp->next==NULL)
        {
            PushBack(newItem);
        }
    }
}// end of InsertBefore
 
template <class ItemType>
void LinkedList<ItemType>::InsertAfter(ItemType initial, ItemType newItem)
{
    node* temp=head;
    node* temp2=new node;
    temp2->info=newItem;
    temp2->next=NULL;
    
    if(IsEmpty())
    {
        PushFront(newItem);
    }
    else if(temp->info==initial)
    {
        temp2->next=temp->next;
        temp->next=temp2;
        ++size;
    }
    else
    {   
        while(temp->next!=NULL)
        {
            if(temp->info==initial)
            {
                temp2->next=temp->next;
                temp->next=temp2;
                ++size;
                break;
            }
            temp=temp->next;
        }
        if(temp->next==NULL)
        {
            PushBack(newItem);
        }
    }
}// end of InsertAfter
 
template <class ItemType>
void LinkedList<ItemType>::InsertInOrder(ItemType item)
{
    if(IsEmpty())
    {
        PushFront(item);
    }
    else
    {
        node* temp=head;
        node* temp2=new node;
    
        if(item <=(temp->info))
        {  
            ItemType placeHolder=temp->info;
            temp2->info=placeHolder;
            temp->info=item;
            temp2->next=temp->next;
            temp->next=temp2;
            ++size;
        } 
        else
        {
            while(temp->next!=NULL)
            {       
                if(((temp->info) <= item) && (item <= (temp->next->info)))
                {           
                    temp2->info=item;
                    temp2->next=temp->next;
                    temp->next=temp2;
                    ++size;
                    return;
                }
                temp=temp->next;
            }
            if(temp->next==NULL)
            {
                PushBack(item);
            }
        }
    }
}// end of InsertInOrder
 
template <class ItemType>
int LinkedList<ItemType>::Size()
{
    if(IsEmpty())
    {
        std::cout<<"\nLIST EMPTY\n";
    }
    return size;
}// end of Size 
 
template <class ItemType>
void LinkedList<ItemType>::MakeEmpty()
{
    if(!IsEmpty())
    {
        std::cout << "\nDestroying nodes...\n";
        while(!IsEmpty())
        {
            node* temp = head;
            //std::cout << temp-> info << '\n';
            head = head-> next;
            delete temp;
        }
        size = 0;
    }
}// end of MakeEmpty
 
template <class ItemType>
LinkedList<ItemType>::~LinkedList()
{
    MakeEmpty();
}// http://programmingnotes.org/

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as its STL counterpart. Here is a sample program demonstrating its use.



		
		
			How To Use #include 'LinkedList.h'
			
C++
			
			#include <iostream>
#include <string>
#include "LinkedList.h"
using namespace std;

int main()
{
    // declare variables, using a string as
    // the item type for the class. 

    // NOTE: you can also use an int, float, double etc.
    // instead of a string
    LinkedList<string> list;

    // demontrate the "InOrder" function
    cout<<"** These are names of fruits sorted in order"
        <<" using the 'InsertInOrder()' function:\n\n";
    list.InsertInOrder("Tomato");
    list.InsertInOrder("Orange");
    list.InsertInOrder("Apple");
    list.InsertInOrder("Plum");
    list.Display();

    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";

    // demonstrate the "Delete" function
    cout<<"\n** Here is the same list with the word 'Plum' deleted"
        << "\nusing the 'Delete()' function:\n\n";
    list.Delete("Plum");
    list.Display();

    cout<<"\nThere is currently "<<list.Size()<<" items in the listnn";

    // demonstrate the "InsertAfter" function
    cout<<"\n** Now the word 'Bike' will be added to the list,"
        <<"\nright after the word 'Apple' using the "
        <<"'InsertAfter()' function:\n\n";
    list.InsertAfter("Apple","Bike");
    list.Display();

    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";

    // demonstrate the "InsertBefore" function
    cout<<"\n** Now the name 'Jessica' will be added to the list,"
        <<"\nright before the word 'Orange' using the "
        <<"'InsertBefore()' function:\n\n";
    list.InsertBefore("Orange","Jessica");
    list.Display();

    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";

    // demonstrate the "Replace" function
    cout<<"\n** The word 'Orange' will now be replaced with the name,"
        <<"\n'Kat' using the 'Replace()' function:\n\n";
    list.Replace("Orange","Kat");
    list.Display();

    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";
}// http://programmingnotes.org/
			
				
					
				
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						#include <iostream>
#include <string>
#include "LinkedList.h"
using namespace std;
 
int main()
{
    // declare variables, using a string as
    // the item type for the class. 
 
    // NOTE: you can also use an int, float, double etc.
    // instead of a string
    LinkedList<string> list;
 
    // demontrate the "InOrder" function
    cout<<"** These are names of fruits sorted in order"
        <<" using the 'InsertInOrder()' function:\n\n";
    list.InsertInOrder("Tomato");
    list.InsertInOrder("Orange");
    list.InsertInOrder("Apple");
    list.InsertInOrder("Plum");
    list.Display();
 
    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";
 
    // demonstrate the "Delete" function
    cout<<"\n** Here is the same list with the word 'Plum' deleted"
        << "\nusing the 'Delete()' function:\n\n";
    list.Delete("Plum");
    list.Display();
 
    cout<<"\nThere is currently "<<list.Size()<<" items in the listnn";
 
    // demonstrate the "InsertAfter" function
    cout<<"\n** Now the word 'Bike' will be added to the list,"
        <<"\nright after the word 'Apple' using the "
        <<"'InsertAfter()' function:\n\n";
    list.InsertAfter("Apple","Bike");
    list.Display();
 
    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";
 
    // demonstrate the "InsertBefore" function
    cout<<"\n** Now the name 'Jessica' will be added to the list,"
        <<"\nright before the word 'Orange' using the "
        <<"'InsertBefore()' function:\n\n";
    list.InsertBefore("Orange","Jessica");
    list.Display();
 
    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";
 
    // demonstrate the "Replace" function
    cout<<"\n** The word 'Orange' will now be replaced with the name,"
        <<"\n'Kat' using the 'Replace()' function:\n\n";
    list.Replace("Orange","Kat");
    list.Display();
 
    cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";
}// http://programmingnotes.org/

Once compiled, you should get this as your output

** These are names of fruits sorted in order using the 'InsertInOrder()' function:
Apple Orange Plum Tomato There is currently 4 items in the list ** Here is the same list with the word 'Plum' deleted using the 'Delete()' function: Apple Orange Tomato There is currently 3 items in the list ** Now the word 'Bike' will be added to the list, right after the word 'Apple' using the 'InsertAfter()' function: Apple Bike Orange Tomato There is currently 4 items in the list ** Now the name 'Jessica' will be added to the list, right before the word 'Orange' using the 'InsertBefore()' function: Apple Bike Jessica Orange Tomato There is currently 5 items in the list ** The word 'Orange' will now be replaced with the name, 'Kat' using the 'Replace()' function: Apple Bike Jessica Kat Tomato
There is currently 5 items in the list

C++ || Snippet – Singly Linked List Custom Template Queue Sample Code

July 14, 2012 admin No comments

This page will consist of sample code for a custom singly linked list template queue. This implementation differs from the previously highlighted doubly linked list in that this version uses a single node to store its data rather than using two separate nodes (front and rear).

Looking for sample code for a stack? Click here.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

Structs Classes Template Classes - What Are They?'' Queue - What is it? FIFO - First In First Out #include < queue> Linked Lists - How To Use

This template class is a custom duplication of the Standard Template Library (STL) queue class. Whether you like building your own data structures, you simply do not like to use any inbuilt functions, opting to build everything yourself, or your homework requires you make your own data structure, this sample code is really useful. I feel its beneficial building functions such as this, that way you better understand the behind the scene processes.



		
		
			#include 'SingleQueue.h'
			
C++
			
			// ============================================================================
//    Author: K Perkins
//    Date:   Jul 14, 2012
//    Taken From: http://programmingnotes.org/
//    File:  SingleQueue.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a queue. 
// ============================================================================
#include <iostream>

template <class ItemType>
class SingleQueue
{
public:
	SingleQueue();
		/*   Function: Constructor initializes queue 
			Precondition: None
			Postcondition: Defines private variables */
	bool IsEmpty();
		/*   Function: Determines whether queue is empty
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is empty and the
							 function = false if queue is not empty */
	bool  IsFull();
		/*   Function: Determines whether queue is full
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is full and the
							 function = false if queue is not full */
	void EnQueue(ItemType item);
		/*   Function: Adds new item to the back of the queue
			Precondition:  Queue has been created and is not full
			Postcondition: Item is in the queue */
	ItemType DeQueue();
		/*   Function: Returns and then deletes the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been removed and the queue
								order is maintained */
	ItemType Front();
		/*   Function: Returns (but does not delete) the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been returned and the queue
								order is maintained */
	ItemType Rear();
		/*   Function: Returns (but does not delete) the last item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The last item in the queue has been returned and the queue
								order is maintained */
	int Size();
          /*   Function: Return the current size of the queue
               Precondition: Queue has been initialized
               Postcondition: The size of the queue is returned */ 
	void MakeEmpty();
		/*   Function: Initializes queue to an empty state 
			Precondition: Queue has been created
			Postcondition: Queue no longer exists */
	~SingleQueue();
		/*   Function: Removes the queue 
			Precondition: Queue has been declared
			Postcondition: Queue no longer exists */
private:		
	struct  NodeType	
	{			
		ItemType currentItem;		
		NodeType* next;	
	};
	NodeType* head;	// front of queue 
	int size;
};

//=========================  Implementation  ================================//

template<class ItemType>
SingleQueue<ItemType>::SingleQueue()
{
	head = NULL;
	size = 0;
}/* end of SingleQueue */

template<class ItemType>
bool SingleQueue<ItemType>::IsEmpty()
{
	return (head == NULL);
}/* end of IsEmpty */

template<class ItemType>
bool SingleQueue<ItemType>::IsFull()
{
	try
	{
		NodeType* location = new NodeType;
		delete location;
		return false;
	}
	catch(std::bad_alloc&)
	{
		return true;
	}
}/* end of IsFull */

template<class ItemType>
void SingleQueue<ItemType>::EnQueue(ItemType newItem)
{
	if(IsFull())
	{
		std::cout<<"nQUEUE FULLn";
	}
	else
	{
		NodeType* newNode = new NodeType;  // adds new node
		newNode-> currentItem = newItem;
		newNode-> next = NULL;
	
		if(IsEmpty())
		{
			head = newNode;
		}
		else
		{
			NodeType* tempPtr = head;
			while(tempPtr-> next != NULL)
			{
				tempPtr = tempPtr-> next;
			}
			tempPtr-> next = newNode;
		}
		++size;
	}
}/* end of EnQueue */

template<class ItemType>
ItemType SingleQueue<ItemType>::DeQueue() 
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    else
    {
        NodeType* tempPtr = head;  // temporary pointer
		
        ItemType item = head-> currentItem;
        head = head-> next;
        delete tempPtr;
        --size;
        return item;
    }	
}/* end of DeQueue */

template<class ItemType>
ItemType SingleQueue<ItemType>::Front() 
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    else
    {	
        ItemType item = head-> currentItem;
        return item;
    }	
}/* end of Front */

template<class ItemType>
ItemType SingleQueue<ItemType>::Rear() 
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    else
    {
        NodeType* tempPtr = head;  // temporary pointer

        while(tempPtr->next != NULL)
        {
                tempPtr = tempPtr-> next;
        }
        ItemType item = tempPtr-> currentItem;
        return item;
    }	
}/* end of Rear */

template<class ItemType>
int SingleQueue<ItemType>::Size()
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    return size;
}/* end of Size */

template<class ItemType>
void SingleQueue<ItemType>::MakeEmpty()
{
    if(!IsEmpty())
    {
        std::cout << "Destroying nodes ...n";
        while(!IsEmpty())
        {
            NodeType* tempPtr = head;
            //std::cout << tempPtr-> currentItem << 'n';
            head = head-> next;
            delete tempPtr;
        }
        size = 0;
    }
}/* end of MakeEmpty */

template<class ItemType>
SingleQueue<ItemType>::~SingleQueue() 
{
	MakeEmpty();
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: K Perkins
//    Date:   Jul 14, 2012
//    Taken From: http://programmingnotes.org/
//    File:  SingleQueue.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a queue. 
// ============================================================================
#include <iostream>
 
template <class ItemType>
class SingleQueue
{
public:
	SingleQueue();
		/*   Function: Constructor initializes queue 
			Precondition: None
			Postcondition: Defines private variables */
	bool IsEmpty();
		/*   Function: Determines whether queue is empty
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is empty and the
							 function = false if queue is not empty */
	bool  IsFull();
		/*   Function: Determines whether queue is full
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is full and the
							 function = false if queue is not full */
	void EnQueue(ItemType item);
		/*   Function: Adds new item to the back of the queue
			Precondition:  Queue has been created and is not full
			Postcondition: Item is in the queue */
	ItemType DeQueue();
		/*   Function: Returns and then deletes the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been removed and the queue
								order is maintained */
	ItemType Front();
		/*   Function: Returns (but does not delete) the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been returned and the queue
								order is maintained */
	ItemType Rear();
		/*   Function: Returns (but does not delete) the last item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The last item in the queue has been returned and the queue
								order is maintained */
	int Size();
          /*   Function: Return the current size of the queue
               Precondition: Queue has been initialized
               Postcondition: The size of the queue is returned */ 
	void MakeEmpty();
		/*   Function: Initializes queue to an empty state 
			Precondition: Queue has been created
			Postcondition: Queue no longer exists */
	~SingleQueue();
		/*   Function: Removes the queue 
			Precondition: Queue has been declared
			Postcondition: Queue no longer exists */
private:		
	struct  NodeType	
	{			
		ItemType currentItem;		
		NodeType* next;	
	};
	NodeType* head;	// front of queue 
	int size;
};
 
//=========================  Implementation  ================================//
 
template<class ItemType>
SingleQueue<ItemType>::SingleQueue()
{
	head = NULL;
	size = 0;
}/* end of SingleQueue */
 
template<class ItemType>
bool SingleQueue<ItemType>::IsEmpty()
{
	return (head == NULL);
}/* end of IsEmpty */
 
template<class ItemType>
bool SingleQueue<ItemType>::IsFull()
{
	try
	{
		NodeType* location = new NodeType;
		delete location;
		return false;
	}
	catch(std::bad_alloc&)
	{
		return true;
	}
}/* end of IsFull */
 
template<class ItemType>
void SingleQueue<ItemType>::EnQueue(ItemType newItem)
{
	if(IsFull())
	{
		std::cout<<"nQUEUE FULLn";
	}
	else
	{
		NodeType* newNode = new NodeType;  // adds new node
		newNode-> currentItem = newItem;
		newNode-> next = NULL;
	
		if(IsEmpty())
		{
			head = newNode;
		}
		else
		{
			NodeType* tempPtr = head;
			while(tempPtr-> next != NULL)
			{
				tempPtr = tempPtr-> next;
			}
			tempPtr-> next = newNode;
		}
		++size;
	}
}/* end of EnQueue */
 
template<class ItemType>
ItemType SingleQueue<ItemType>::DeQueue() 
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    else
    {
        NodeType* tempPtr = head;  // temporary pointer
		
        ItemType item = head-> currentItem;
        head = head-> next;
        delete tempPtr;
        --size;
        return item;
    }	
}/* end of DeQueue */
 
template<class ItemType>
ItemType SingleQueue<ItemType>::Front() 
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    else
    {	
        ItemType item = head-> currentItem;
        return item;
    }	
}/* end of Front */
 
template<class ItemType>
ItemType SingleQueue<ItemType>::Rear() 
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    else
    {
        NodeType* tempPtr = head;  // temporary pointer
 
        while(tempPtr->next != NULL)
        {
                tempPtr = tempPtr-> next;
        }
        ItemType item = tempPtr-> currentItem;
        return item;
    }	
}/* end of Rear */
 
template<class ItemType>
int SingleQueue<ItemType>::Size()
{
    if(IsEmpty())
    {
        std::cout<<"nQUEUE EMPTYn";
    }
    return size;
}/* end of Size */
 
template<class ItemType>
void SingleQueue<ItemType>::MakeEmpty()
{
    if(!IsEmpty())
    {
        std::cout << "Destroying nodes ...n";
        while(!IsEmpty())
        {
            NodeType* tempPtr = head;
            //std::cout << tempPtr-> currentItem << 'n';
            head = head-> next;
            delete tempPtr;
        }
        size = 0;
    }
}/* end of MakeEmpty */
 
template<class ItemType>
SingleQueue<ItemType>::~SingleQueue() 
{
	MakeEmpty();
}// http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as its STL counterpart. Here is a sample program demonstrating its use.



		
		
			How To Use #include 'SingleQueue.h'
			
C++
			
			#include <iostream>
#include "SingleQueue.h"
using namespace std;

int main()
{
	// declare variables
	SingleQueue<char> charQueue;
	SingleQueue<int> intQueue;
	SingleQueue<double> doubleQueue;
	
	// ------ Char Example ------//
	char charArry[]="My Programming Notes Is A Big Help!";
	int counter=0;	
	while(charArry[counter]!='\0')
	{
		charQueue.EnQueue(charArry[counter]);
		++counter;
	}
	cout<<"charQueue has "<<charQueue.Size()<<" items in it "
		<<"and contains the text:n";
	while(!charQueue.IsEmpty())
	{
		cout<<charQueue.DeQueue();
	}
	cout<<endl;
	
	// ------ Int Example ------//
	int intArry[]={1,22,309,461,-92,66,7,8,1987,9,27,12};
	counter=0;
	while(counter < sizeof(intArry)/sizeof(intArry[0]))
	{
		intQueue.EnQueue(intArry[counter]);
		++counter;
	}
	cout<<"nintQueue has "<<intQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	counter=0;
	while(!intQueue.IsEmpty())
	{
		counter-=intQueue.DeQueue();
	}
	cout<<counter<<endl;
	
	// ------ Double Example ------//
	double doubleArry[]={31.62,2.8,43.9,4.4,19.87,6.23,7.787,68.99,9.6,3.540,12.04};
	double sum=0;
	counter=0;
	while(counter < sizeof(doubleArry)/sizeof(doubleArry[0]))
	{
		doubleQueue.EnQueue(doubleArry[counter]);
		++counter;
	}
	cout<<"ndoubleQueue has "<<doubleQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	while(!doubleQueue.IsEmpty())
	{
		sum+=doubleQueue.DeQueue();
	}
	cout<<sum<<endl;

	return 0;
}// http://programmingnotes.org/
			
				
					
				
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						#include <iostream>
#include "SingleQueue.h"
using namespace std;
 
int main()
{
	// declare variables
	SingleQueue<char> charQueue;
	SingleQueue<int> intQueue;
	SingleQueue<double> doubleQueue;
	
	// ------ Char Example ------//
	char charArry[]="My Programming Notes Is A Big Help!";
	int counter=0;	
	while(charArry[counter]!='\0')
	{
		charQueue.EnQueue(charArry[counter]);
		++counter;
	}
	cout<<"charQueue has "<<charQueue.Size()<<" items in it "
		<<"and contains the text:n";
	while(!charQueue.IsEmpty())
	{
		cout<<charQueue.DeQueue();
	}
	cout<<endl;
	
	// ------ Int Example ------//
	int intArry[]={1,22,309,461,-92,66,7,8,1987,9,27,12};
	counter=0;
	while(counter < sizeof(intArry)/sizeof(intArry[0]))
	{
		intQueue.EnQueue(intArry[counter]);
		++counter;
	}
	cout<<"nintQueue has "<<intQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	counter=0;
	while(!intQueue.IsEmpty())
	{
		counter-=intQueue.DeQueue();
	}
	cout<<counter<<endl;
	
	// ------ Double Example ------//
	double doubleArry[]={31.62,2.8,43.9,4.4,19.87,6.23,7.787,68.99,9.6,3.540,12.04};
	double sum=0;
	counter=0;
	while(counter < sizeof(doubleArry)/sizeof(doubleArry[0]))
	{
		doubleQueue.EnQueue(doubleArry[counter]);
		++counter;
	}
	cout<<"ndoubleQueue has "<<doubleQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	while(!doubleQueue.IsEmpty())
	{
		sum+=doubleQueue.DeQueue();
	}
	cout<<sum<<endl;
 
	return 0;
}// http://programmingnotes.org/

Once compiled, you should get this as your output

charQueue has 35 items in it and contains the text: My Programming Notes Is A Big Help!
intQueue has 12 items in it. The sum of the numbers in the queue is: -2817
doubleQueue has 11 items in it. The sum of the numbers in the queue is: 210.777 Press any key to continue . . .

C++ || Snippet – Doubly Linked List Custom Template Queue Sample Code

May 20, 2012 admin No comments

This page will consist of sample code for a custom doubly linked list template queue. This implementation is considered a doubly linked list because it uses two nodes to store data in the queue – a ‘front’ and a ‘rear’ node. This is not a circular linked list, nor does it link forwards and/or backwards.

Looking for sample code for a stack? Click here.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

Structs Classes Template Classes - What Are They? Queue - What is it? FIFO - First In First Out #include < queue> Linked Lists - How To Use



		
		
			#include 'DoubleQueue.h'
			
C++
			
			// ============================================================================
//    Author: K Perkins
//    Date:   May 20, 2012
//    Taken From: http://programmingnotes.org/
//    File:  DoubleQueue.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a queue. 
// ============================================================================
#include <iostream>

template <class ItemType>
class DoubleQueue
{
public:
	DoubleQueue();
		/*   Function: Constructor initializes queue 
			Precondition: None
			Postcondition: Defines private variables */
	bool IsEmpty();
		/*   Function: Determines whether queue is empty
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is empty and the
							 function = false if queue is not empty */
	bool  IsFull();
		/*   Function: Determines whether queue is full
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is full and the
							 function = false if queue is not full */
	void EnQueue(ItemType item);
		/*   Function: Adds new item to the back of the queue
			Precondition:  Queue has been created and is not full
			Postcondition: Item is in the queue */
	ItemType DeQueue();
		/*   Function: Returns and then deletes the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been removed and the queue
								order is maintained */
	ItemType Front();
		/*   Function: Returns (but does not delete) the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been returned and the queue
								order is maintained */
	ItemType Rear();
		/*   Function: Returns (but does not delete) the last item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The last item in the queue has been returned and the queue
								order is maintained */
	int Size();
          /*   Function: Return the current size of the queue
               Precondition: Queue has been initialized
               Postcondition: The size of the queue is returned */ 
	void MakeEmpty();
		/*   Function: Initializes queue to an empty state 
			Precondition: Queue has been created
			Postcondition: Queue no longer exists */
	~DoubleQueue();
		/*   Function: Removes the queue 
			Precondition: Queue has been declared
			Postcondition: Queue no longer exists */
private:
	struct  NodeType
	{
		ItemType currentItem;
		NodeType* next;
	};
	NodeType* front;	// front of queue 
	NodeType* rear;		// back of queue
	int size;
};

//=========================  Implementation  ================================//

template<class ItemType>
DoubleQueue<ItemType>::DoubleQueue()
{
	front = NULL;
	rear = NULL;
	size = 0;
}/* end of DoubleQueue */

template<class ItemType>
bool DoubleQueue<ItemType>::IsEmpty()
{
	return (front == NULL);
}/* end of IsEmpty */

template<class ItemType>
bool DoubleQueue<ItemType>::IsFull()
{	
	try
	{
		NodeType* location = new NodeType;
		delete location;
		return false;
	}
	catch(std::bad_alloc&)
	{
		return true;
	}
}/* end of IsFull */

template<class ItemType>
void DoubleQueue<ItemType>::EnQueue(ItemType newItem)
{
	if(IsFull())
	{
		std::cout<<"nQUEUE FULLn";
	}
	else
	{
		NodeType* newNode = new NodeType; // adds new node
		newNode-> currentItem = newItem;
		newNode-> next = NULL;
	
		if(rear == NULL)
		{
			front = newNode;
		}
		else
		{
			rear-> next = newNode;			
		}
		rear = newNode;
		++size;
	}
}/* end of EnQueue */

template<class ItemType>
ItemType DoubleQueue<ItemType>::DeQueue() 
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	else
	{
		NodeType* tempPtr = front; // temporary pointer
		
		ItemType item = front-> currentItem;
		front = front-> next;

		if(front == NULL)
		{
			rear = NULL;
		}
		delete tempPtr;
		--size;
		return item;
	}	
}/* end of DeQueue */

template<class ItemType>
ItemType DoubleQueue<ItemType>::Front() 
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	else
	{
		return front-> currentItem;
	}	
}/* end of Front */

template<class ItemType>
ItemType DoubleQueue<ItemType>::Rear() 
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	else
	{		
		return rear-> currentItem;
	}	
}/* end of Rear */

template<class ItemType>
int DoubleQueue<ItemType>::Size()
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	return size;
}/* end of Size */

template<class ItemType>
void DoubleQueue<ItemType>::MakeEmpty()
{
	if(!IsEmpty())
	{
		std::cout << "Destroying nodes ...n";
		while(!IsEmpty())
		{
			NodeType* tempPtr = front;
			//std::cout << tempPtr-> currentItem << 'n';
			front = front-> next;
			delete tempPtr;
		}
		rear = NULL;
		size = 0;
	}
}/* end of MakeEmpty */

template<class ItemType>
DoubleQueue<ItemType>::~DoubleQueue() 
{
	MakeEmpty();
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: K Perkins
//    Date:   May 20, 2012
//    Taken From: http://programmingnotes.org/
//    File:  DoubleQueue.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a queue. 
// ============================================================================
#include <iostream>
 
template <class ItemType>
class DoubleQueue
{
public:
	DoubleQueue();
		/*   Function: Constructor initializes queue 
			Precondition: None
			Postcondition: Defines private variables */
	bool IsEmpty();
		/*   Function: Determines whether queue is empty
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is empty and the
							 function = false if queue is not empty */
	bool  IsFull();
		/*   Function: Determines whether queue is full
			Precondition: Queue has been created
			Postcondition: The function = true if the queue is full and the
							 function = false if queue is not full */
	void EnQueue(ItemType item);
		/*   Function: Adds new item to the back of the queue
			Precondition:  Queue has been created and is not full
			Postcondition: Item is in the queue */
	ItemType DeQueue();
		/*   Function: Returns and then deletes the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been removed and the queue
								order is maintained */
	ItemType Front();
		/*   Function: Returns (but does not delete) the first item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The first item in the queue has been returned and the queue
								order is maintained */
	ItemType Rear();
		/*   Function: Returns (but does not delete) the last item in the queue
			Precondition:  Queue has been created and is not empty
			Postcondition: The last item in the queue has been returned and the queue
								order is maintained */
	int Size();
          /*   Function: Return the current size of the queue
               Precondition: Queue has been initialized
               Postcondition: The size of the queue is returned */ 
	void MakeEmpty();
		/*   Function: Initializes queue to an empty state 
			Precondition: Queue has been created
			Postcondition: Queue no longer exists */
	~DoubleQueue();
		/*   Function: Removes the queue 
			Precondition: Queue has been declared
			Postcondition: Queue no longer exists */
private:
	struct  NodeType
	{
		ItemType currentItem;
		NodeType* next;
	};
	NodeType* front;	// front of queue 
	NodeType* rear;		// back of queue
	int size;
};
 
//=========================  Implementation  ================================//
 
template<class ItemType>
DoubleQueue<ItemType>::DoubleQueue()
{
	front = NULL;
	rear = NULL;
	size = 0;
}/* end of DoubleQueue */
 
template<class ItemType>
bool DoubleQueue<ItemType>::IsEmpty()
{
	return (front == NULL);
}/* end of IsEmpty */
 
template<class ItemType>
bool DoubleQueue<ItemType>::IsFull()
{	
	try
	{
		NodeType* location = new NodeType;
		delete location;
		return false;
	}
	catch(std::bad_alloc&)
	{
		return true;
	}
}/* end of IsFull */
 
template<class ItemType>
void DoubleQueue<ItemType>::EnQueue(ItemType newItem)
{
	if(IsFull())
	{
		std::cout<<"nQUEUE FULLn";
	}
	else
	{
		NodeType* newNode = new NodeType; // adds new node
		newNode-> currentItem = newItem;
		newNode-> next = NULL;
	
		if(rear == NULL)
		{
			front = newNode;
		}
		else
		{
			rear-> next = newNode;			
		}
		rear = newNode;
		++size;
	}
}/* end of EnQueue */
 
template<class ItemType>
ItemType DoubleQueue<ItemType>::DeQueue() 
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	else
	{
		NodeType* tempPtr = front; // temporary pointer
		
		ItemType item = front-> currentItem;
		front = front-> next;
 
		if(front == NULL)
		{
			rear = NULL;
		}
		delete tempPtr;
		--size;
		return item;
	}	
}/* end of DeQueue */
 
template<class ItemType>
ItemType DoubleQueue<ItemType>::Front() 
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	else
	{
		return front-> currentItem;
	}	
}/* end of Front */
 
template<class ItemType>
ItemType DoubleQueue<ItemType>::Rear() 
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	else
	{		
		return rear-> currentItem;
	}	
}/* end of Rear */
 
template<class ItemType>
int DoubleQueue<ItemType>::Size()
{
	if(IsEmpty())
	{
		std::cout<<"nQUEUE EMPTYn";
	}
	return size;
}/* end of Size */
 
template<class ItemType>
void DoubleQueue<ItemType>::MakeEmpty()
{
	if(!IsEmpty())
	{
		std::cout << "Destroying nodes ...n";
		while(!IsEmpty())
		{
			NodeType* tempPtr = front;
			//std::cout << tempPtr-> currentItem << 'n';
			front = front-> next;
			delete tempPtr;
		}
		rear = NULL;
		size = 0;
	}
}/* end of MakeEmpty */
 
template<class ItemType>
DoubleQueue<ItemType>::~DoubleQueue() 
{
	MakeEmpty();
}// http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as its STL counterpart. Here is a sample program demonstrating its use.



		
		
			How To Use #include 'DoubleQueue.h'
			
C++
			
			#include <iostream>
#include "DoubleQueue.h"
using namespace std;

int main()
{
	// declare variables
	DoubleQueue<char> charQueue;
	DoubleQueue<int> intQueue;
	DoubleQueue<float> floatQueue;
	
	// ------ Char Example ------//
	char charArry[]="My Programming Notes Helped Me Succeed!";
	int counter=0;	
	while(charArry[counter]!='\0')
	{
		charQueue.EnQueue(charArry[counter]);
		++counter;
	}
	cout<<"charQueue has "<<charQueue.Size()<<" items in it "
		<<"and contains the text:n";
	while(!charQueue.IsEmpty())
	{
		cout<<charQueue.DeQueue();
	}
	cout<<endl;
	
	// ------ Int Example ------//
	int intArry[]={1,22,3,46,5,66,7,8,1987};
	counter=0;
	while(counter<9)
	{
		intQueue.EnQueue(intArry[counter]);
		++counter;
	}
	cout<<"nintQueue has "<<intQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	counter=0;
	while(!intQueue.IsEmpty())
	{
		counter-=intQueue.DeQueue();
	}
	cout<<counter<<endl;
	
	// ------ Float Example ------//
	float floatArry[]={41.6,2.8,43.9,4.4,19.87,6.23,7.787,68.99,9.6,81.540};
	float sum=0;
	counter=0;
	while(counter<10)
	{
		floatQueue.EnQueue(floatArry[counter]);
		++counter;
	}
	cout<<"nfloatQueue has "<<floatQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	while(!floatQueue.IsEmpty())
	{
		sum-=floatQueue.DeQueue();
	}
	cout<<sum<<endl;

	return 0;
}// http://programmingnotes.org/
			
				
					
				
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						#include <iostream>
#include "DoubleQueue.h"
using namespace std;
 
int main()
{
	// declare variables
	DoubleQueue<char> charQueue;
	DoubleQueue<int> intQueue;
	DoubleQueue<float> floatQueue;
	
	// ------ Char Example ------//
	char charArry[]="My Programming Notes Helped Me Succeed!";
	int counter=0;	
	while(charArry[counter]!='\0')
	{
		charQueue.EnQueue(charArry[counter]);
		++counter;
	}
	cout<<"charQueue has "<<charQueue.Size()<<" items in it "
		<<"and contains the text:n";
	while(!charQueue.IsEmpty())
	{
		cout<<charQueue.DeQueue();
	}
	cout<<endl;
	
	// ------ Int Example ------//
	int intArry[]={1,22,3,46,5,66,7,8,1987};
	counter=0;
	while(counter<9)
	{
		intQueue.EnQueue(intArry[counter]);
		++counter;
	}
	cout<<"nintQueue has "<<intQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	counter=0;
	while(!intQueue.IsEmpty())
	{
		counter-=intQueue.DeQueue();
	}
	cout<<counter<<endl;
	
	// ------ Float Example ------//
	float floatArry[]={41.6,2.8,43.9,4.4,19.87,6.23,7.787,68.99,9.6,81.540};
	float sum=0;
	counter=0;
	while(counter<10)
	{
		floatQueue.EnQueue(floatArry[counter]);
		++counter;
	}
	cout<<"nfloatQueue has "<<floatQueue.Size()<<" items in it.n"
		<<"The sum of the numbers in the queue is: ";
	while(!floatQueue.IsEmpty())
	{
		sum-=floatQueue.DeQueue();
	}
	cout<<sum<<endl;
 
	return 0;
}// http://programmingnotes.org/

Once compiled, you should get this as your output

charQueue has 39 items in it and contains the text: My Programming Notes Helped Me Succeed!
intQueue has 9 items in it. The sum of the numbers in the queue is: -2145
floatQueue has 10 items in it. The sum of the numbers in the queue is: -286.717

C++ || Snippet – Linked List Custom Template Stack Sample Code

April 09, 2012 admin No comments

This page will consist of sample code for a custom linked list template stack. This page differs from the previously highlighted array based template stack in that this version uses a singly linked list to store data rather than using an array.

Looking for sample code for a queue? Click here.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

Structs Classes Template Classes - What Are They? Stacks LIFO - What Is It? #include < stack> Linked Lists - How To Use

This template class is a custom duplication of the Standard Template Library (STL) stack class. Whether you like building your own data structures, you simply do not like to use any inbuilt functions, opting to build everything yourself, or your homework requires you make your own data structure, this sample code is really useful. I feel its beneficial building functions such as this, that way you better understand the behind the scene processes.



		
		
			#include 'ClassStackListType.h'
			
C++
			
			// ============================================================================
//    Author: K Perkins
//    Date:   Apr 9, 2012
//    Taken From: http://programmingnotes.org/
//    File:  ClassStackListType.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a stack. 
// ============================================================================
#include <iostream>         

template <class ItemType>
class StackListType
{
public:
    StackListType();
          /*   Function: constructor initializes class variables 
               Precondition: none
               Postcondition: defines private variables */
    bool IsEmpty();
          /*   Function: Determines whether the stack is empty
               Precondition: Stack has been initialized
               Postcondition: Function value = (stack is empty) */
    bool IsFull();
          /*   Function: Determines whether the stack is full
               Precondition: Stack has been initialized
               Postcondition: Function value = (stack is full) */
    int Size();
          /*   Function: Return the current size of the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is full) exception FullStack is thrown
                                   else newItem is at the top of the stack */
    void MakeEmpty();
          /*   Function: Empties the stack
               Precondition: Stack has been initialized
               Postcondition: Stack is empty */
    void Push(ItemType newItem);
          /*   Function: Adds newItem to the top of the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is full) exception FullStack is thrown
                                   else newItem is at the top of the stack */
    ItemType Pop();
          /*   Function: Returns & then removes top item from the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is empty) exception EmptyStack is thrown
                                   else top element has been removed from the stack */
    ItemType Top();
          /*   Function: Returns the top item from the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is empty) exception EmptyStack is thrown
                                   else top element has been removed from the stack */
    ~StackListType();
          /*   Function: destructor deallocates class variables 
               Precondition: none
               Postcondition: deallocates private variables */

private:
    struct NodeType
    {
          ItemType currentItem;  // Variable which hold all the incoming currentItem
          NodeType* next; // Creates a pointer that points to the next node in the list.
    };
    int size;          // Indicates the size of the stack	
    ItemType junk;
    NodeType* headPtr; // Creates a head pointer that will point to the begining of the list.
};

//=========================  Implementation  ================================//

template<class ItemType>
StackListType<ItemType>::StackListType()
{
    size = 0;
    headPtr = NULL;
}//     End of StackListType

template<class ItemType>
bool StackListType<ItemType>::IsEmpty()
{
    return (headPtr == NULL);
}//     End of IsEmpty

template<class ItemType>
bool StackListType<ItemType>::IsFull()
{    
    try
    {
        NodeType* tempPtr = new NodeType;
        delete tempPtr;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}//     End of IsFull

template<class ItemType>
int StackListType<ItemType>::Size()
{
    if(IsEmpty())
    {
        std::cout<<"nSTACK EMPTYn";
    }
    return size;
}//     End of Size

template<class ItemType>
void StackListType<ItemType>::MakeEmpty()
{
    size = 0;    
	
    if (!IsEmpty())
	{
        std::cout << "Destroying nodes ...n";

		while (!IsEmpty())
		{
			NodeType* tempPtr = headPtr;
			//std::cout << tempPtr-> currentItem << 'n';
			headPtr = headPtr-> next;
			delete tempPtr;
		}
	}     
}//     End of MakeEmpty

template<class ItemType>
void StackListType<ItemType>::Push(ItemType newItem)
{
    if(IsFull())
    {
        std::cout<<"nSTACK FULLn";
        return;
    }
    NodeType* tempPtr = new NodeType;
    tempPtr-> currentItem = newItem;
    tempPtr-> next = headPtr;
    headPtr = tempPtr;
    ++size;
}//     End of Push

template<class ItemType>
ItemType StackListType<ItemType>::Pop()
{
    if(IsEmpty())
    {
        std::cout<<"nSTACK EMPTYn";
        return junk;
    }
    else
    {  
        ItemType data = headPtr-> currentItem;  
        NodeType* tempPtr = headPtr;
        headPtr = headPtr-> next;
        delete tempPtr;
        --size;
        return data;
    }
}//     End of Pop

template<class ItemType>
ItemType StackListType<ItemType>::Top()
{
    if(IsEmpty())
    {
        std::cout<<"nSTACK EMPTYn";
        return junk;
    }
    else
    { 
        return headPtr-> currentItem;
    }
}//     End of Top

template<class ItemType>
StackListType<ItemType>::~StackListType()
{
    MakeEmpty();   
}// http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: K Perkins
//    Date:   Apr 9, 2012
//    Taken From: http://programmingnotes.org/
//    File:  ClassStackListType.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a stack. 
// ============================================================================
#include <iostream>         
 
template <class ItemType>
class StackListType
{
public:
    StackListType();
          /*   Function: constructor initializes class variables 
               Precondition: none
               Postcondition: defines private variables */
    bool IsEmpty();
          /*   Function: Determines whether the stack is empty
               Precondition: Stack has been initialized
               Postcondition: Function value = (stack is empty) */
    bool IsFull();
          /*   Function: Determines whether the stack is full
               Precondition: Stack has been initialized
               Postcondition: Function value = (stack is full) */
    int Size();
          /*   Function: Return the current size of the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is full) exception FullStack is thrown
                                   else newItem is at the top of the stack */
    void MakeEmpty();
          /*   Function: Empties the stack
               Precondition: Stack has been initialized
               Postcondition: Stack is empty */
    void Push(ItemType newItem);
          /*   Function: Adds newItem to the top of the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is full) exception FullStack is thrown
                                   else newItem is at the top of the stack */
    ItemType Pop();
          /*   Function: Returns & then removes top item from the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is empty) exception EmptyStack is thrown
                                   else top element has been removed from the stack */
    ItemType Top();
          /*   Function: Returns the top item from the stack
               Precondition: Stack has been initialized
               Postcondition: If (stack is empty) exception EmptyStack is thrown
                                   else top element has been removed from the stack */
    ~StackListType();
          /*   Function: destructor deallocates class variables 
               Precondition: none
               Postcondition: deallocates private variables */
 
private:
    struct NodeType
    {
          ItemType currentItem;  // Variable which hold all the incoming currentItem
          NodeType* next; // Creates a pointer that points to the next node in the list.
    };
    int size;          // Indicates the size of the stack	
    ItemType junk;
    NodeType* headPtr; // Creates a head pointer that will point to the begining of the list.
};
 
//=========================  Implementation  ================================//
 
template<class ItemType>
StackListType<ItemType>::StackListType()
{
    size = 0;
    headPtr = NULL;
}//     End of StackListType
 
template<class ItemType>
bool StackListType<ItemType>::IsEmpty()
{
    return (headPtr == NULL);
}//     End of IsEmpty
 
template<class ItemType>
bool StackListType<ItemType>::IsFull()
{    
    try
    {
        NodeType* tempPtr = new NodeType;
        delete tempPtr;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}//     End of IsFull
 
template<class ItemType>
int StackListType<ItemType>::Size()
{
    if(IsEmpty())
    {
        std::cout<<"nSTACK EMPTYn";
    }
    return size;
}//     End of Size
 
template<class ItemType>
void StackListType<ItemType>::MakeEmpty()
{
    size = 0;    
	
    if (!IsEmpty())
	{
        std::cout << "Destroying nodes ...n";
 
		while (!IsEmpty())
		{
			NodeType* tempPtr = headPtr;
			//std::cout << tempPtr-> currentItem << 'n';
			headPtr = headPtr-> next;
			delete tempPtr;
		}
	}     
}//     End of MakeEmpty
 
template<class ItemType>
void StackListType<ItemType>::Push(ItemType newItem)
{
    if(IsFull())
    {
        std::cout<<"nSTACK FULLn";
        return;
    }
    NodeType* tempPtr = new NodeType;
    tempPtr-> currentItem = newItem;
    tempPtr-> next = headPtr;
    headPtr = tempPtr;
    ++size;
}//     End of Push
 
template<class ItemType>
ItemType StackListType<ItemType>::Pop()
{
    if(IsEmpty())
    {
        std::cout<<"nSTACK EMPTYn";
        return junk;
    }
    else
    {  
        ItemType data = headPtr-> currentItem;  
        NodeType* tempPtr = headPtr;
        headPtr = headPtr-> next;
        delete tempPtr;
        --size;
        return data;
    }
}//     End of Pop
 
template<class ItemType>
ItemType StackListType<ItemType>::Top()
{
    if(IsEmpty())
    {
        std::cout<<"nSTACK EMPTYn";
        return junk;
    }
    else
    { 
        return headPtr-> currentItem;
    }
}//     End of Top
 
template<class ItemType>
StackListType<ItemType>::~StackListType()
{
    MakeEmpty();   
}// http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

===== DEMONSTRATION HOW TO USE =====

Use of the above template class is the same as its STL counterpart. Here is a sample program demonstrating its use.



		
		
			How To Use #include 'ClassStackListType.h'
			
C++
			
			#include <iostream>
#include "ClassStackListType.h"
using namespace std;

int  main()
{    // declare variables
     StackListType<char> charStack;
     StackListType<int> intStack;
     StackListType<float> floatStack;
     
     // ------ Char Example ------//
     char charArry[]="My Programming Notes Is Awesome";
     int counter=0;
     while(charArry[counter]!='\0')
     {
          charStack.Push(charArry[counter]);
          ++counter;
     }
     cout<<"charStack has "<<charStack.Size()<<" items in itn"
     <<"and contains the text ""<<charArry<<"" backwards:n";
     while(!charStack.IsEmpty())
     {
          cout<<charStack.Pop();
     }
     cout<<endl;     
     
     // ------ Int Example ------//
     int intArry[]={1,22,3,46,5,66,7,8,1987};
     counter=0;
     while(counter<9)
     {
          intStack.Push(intArry[counter]);
          ++counter;
     }
     cout<<"nintStack has "<<intStack.Size()<<" items in it.n"
     <<"The sum of the numbers in the stack is: ";
     counter=0;
     while(!intStack.IsEmpty())
     {
          counter+=intStack.Pop();
     }
     cout<<counter<<endl;
     
     // ------ Float Example ------//
     float floatArry[]={41.6,2.8,43.9,4.4,19.87,6.23,7.787,68.99,9.6,81.540};
     float sum=0;
     counter=0;
     while(counter<10)
     {
          floatStack.Push(floatArry[counter]);
          ++counter;
     }
     cout<<"nfloatStack has "<<floatStack.Size()<<" items in it.n"
     <<"The sum of the numbers in the stack is: ";
     while(!floatStack.IsEmpty())
     {
          sum+=floatStack.Pop();
     }
     cout<<sum<<endl;     
}// http://programmingnotes.org/
			
				
					
				
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						#include <iostream>
#include "ClassStackListType.h"
using namespace std;
 
int  main()
{    // declare variables
     StackListType<char> charStack;
     StackListType<int> intStack;
     StackListType<float> floatStack;
     
     // ------ Char Example ------//
     char charArry[]="My Programming Notes Is Awesome";
     int counter=0;
     while(charArry[counter]!='\0')
     {
          charStack.Push(charArry[counter]);
          ++counter;
     }
     cout<<"charStack has "<<charStack.Size()<<" items in itn"
     <<"and contains the text ""<<charArry<<"" backwards:n";
     while(!charStack.IsEmpty())
     {
          cout<<charStack.Pop();
     }
     cout<<endl;     
     
     // ------ Int Example ------//
     int intArry[]={1,22,3,46,5,66,7,8,1987};
     counter=0;
     while(counter<9)
     {
          intStack.Push(intArry[counter]);
          ++counter;
     }
     cout<<"nintStack has "<<intStack.Size()<<" items in it.n"
     <<"The sum of the numbers in the stack is: ";
     counter=0;
     while(!intStack.IsEmpty())
     {
          counter+=intStack.Pop();
     }
     cout<<counter<<endl;
     
     // ------ Float Example ------//
     float floatArry[]={41.6,2.8,43.9,4.4,19.87,6.23,7.787,68.99,9.6,81.540};
     float sum=0;
     counter=0;
     while(counter<10)
     {
          floatStack.Push(floatArry[counter]);
          ++counter;
     }
     cout<<"nfloatStack has "<<floatStack.Size()<<" items in it.n"
     <<"The sum of the numbers in the stack is: ";
     while(!floatStack.IsEmpty())
     {
          sum+=floatStack.Pop();
     }
     cout<<sum<<endl;     
}// http://programmingnotes.org/

Once compiled, you should get this as your output

charStack has 31 items in it and contains the text "My Programming Notes Is Awesome" backwards: emosewA sI setoN gnimmargorP yM
intStack has 9 items in it. The sum of the numbers in the stack is: 2145
floatStack has 10 items in it. The sum of the numbers in the stack is: 286.717

C++ || Multi Process Server & Client Hash Table Using Thread Pools, Message Queues, & Signal Handlers

October 05, 2013 admin No comments

The following is another homework assignment which was presented in an Operating Systems Concepts class. Using commandline arguments, the following is a program which implements a multi threaded hash table, utilizing message queues to pass text from a client program to a server program and vice versa. This program makes use of multiple interprocess communication function calls provided on Unix based systems.

REQUIRED KNOWLEDGE FOR THIS PROGRAM

How To Override The Default Signal Handler (CTRL-C) How To Create And Use Pthreads For Interprocess Communication How To Use Message Queues For Interprocess Communication Multi Process Synchronization Producer Consumer Problem Using Pthreads Sample Input Server Records File - Download Here

==== 1. OVERVIEW ====

Hash tables are widely used for efficient storage and retrieval of data. When using hash tables in multi threaded applications, you must ensure that concurrent accesses into the hash table is free from race conditions, dead locks, and other problems that arise in program synchronization.

One solution to overcome this problem is to prevent concurrent accesses into the hash table altogether; i.e. prior to accessing the hash table, a thread acquires a lock, and then releases the lock after the access is complete. Such approach, although simple, is inefficient. The program demonstrated on this page implements an alternative solution, one which permits safe concurrent accesses into the hash table. In the approach implemented on this page, each hash location within a hash table is protected with a separate lock. Hence, multiple threads access the hash table concurrently as long as they are accessing different hash locations. For greater efficiency, this program also makes use of a thread pool.

==== 2. TECHNICAL DETAILS ====

This program was implemented in two parts; a server program and a client program. The server side of the program maintains a hash table of records and a pool of threads. The client program requests from the server program search records by sending record ids over a message queue. The server program then retrieves a request from the message queue, and wakes up a thread in the thread pool. That awakened thread then uses the id (sent from the client program) to retrieve the corresponding record from the hash table, and sends the found record from the server program to the client program over the message queue.

The server also reads a specified file from the commandline, which stores initial user data that is to be inserted and stored into the hash table. The incoming text file has the following format:

a unique numerical id 1 (an integer) the first name 1 (a string) the last name 1 (a string) . . . a unique numerical id N (an integer) the first name N (a string) the last name N (a string)

These three fields make up one single record for one individual. More than one record may be present in the incoming text file.

==== 3. SERVER ====

The server has the following structure and function:

Multi Threaded Process Server Flow Control	Select Show
1. The server is invoked with two command line arguments specifying: • The name of the file storing a list of records. • The number of threads. 2. The server reads the specified file, then stores the records in the hash table. The hash table has the following structure and function: • The hash table is an array of 100 cells. • Each cell contains two items (1) a lock (mutex) protecting the cell; and (2) a linked-list of records hashing to the cell. • The hash table supports methods for inserting and retrieving records. • The hash keys of records are computed as record id mod hash table size where record id is the id associated with each record. 3. Creates a message queue using msgget() system call. 4. Creates the specified number of threads. 5. Each thread joins a thread pool. 6. The parent thread then checks the message queue for new messages using msgrcv() system call. 7. When a new message arrives the parent thread retrieves the message, adds it to a list of received messages, and wakes up a thread from the thread pool. 8. The awakened thread removes a message from the list and checks the id contained in the message. The id indicates that the client who sent the message wants to know the record associated with the respective id. 9. The thread then checks if the record with a given id exists in the table and if so retrieves it. The retrieved record is then sent to the client over the message queue. If the record does not exist, then the server sends back a record with id field set to -1. 10. The thread then removes the next message from the list and repeats the same process. If the list is empty, then the thread goes back to the thread pool. 11. The server also simulates a scenario where the hash table is constantly being updated with new records. You will simulate this by using 5 separate threads that periodically (e.g. every 1 second) randomly generate records and insert them into the hash table. 12. When the user presses Ctrl-c, the server catches the SIGINT signal, removes the message queue using msgctl(), deallocates any other resources (e.g. mutexes, condition variables, etc) and exits. To intercept the signal you will need to define a custom signal handler.

Multi Threaded Process Server Flow Control

Select Show

1. The server is invoked with two command line arguments specifying:

2. The server reads the specified file, then stores the records in the hash table. The hash table has the following structure and function:

record id

hash table size

record id

3. Creates a message queue using msgget() system call.

4. Creates the specified number of threads.

5. Each thread joins a thread pool.

6. The parent thread then checks the message queue for new messages using msgrcv() system call.

7. When a new message arrives the parent thread retrieves the message, adds it to a list of received messages, and wakes up a thread from the thread pool.

8. The awakened thread removes a message from the list and checks the id contained in the message. The id indicates that the client who sent the message wants to know the record associated with the respective id.

9. The thread then checks if the record with a given id exists in the table and if so retrieves it. The retrieved record is then sent to the client over the message queue. If the record does not exist, then the server sends back a record with id field set to -1.

10. The thread then removes the next message from the list and repeats the same process. If the list is empty, then the thread goes back to the thread pool.

11. The server also simulates a scenario where the hash table is constantly being updated with new records. You will simulate this by using 5 separate threads that periodically (e.g. every 1 second) randomly generate records and insert them into the hash table.

12. When the user presses Ctrl-c, the server catches the SIGINT signal, removes the message queue using msgctl(), deallocates any other resources (e.g. mutexes, condition variables, etc) and exits. To intercept the signal you will need to define a custom signal handler.

The server program is invoked with the following commandline structure:

./Server [FILE NAME] [NUMBER OF THREADS] (e.g. ./Server database.dat 10)

The server is implemented below.



		
		
			Multi Threaded Process Server With Hash Table
			
C++
			
			// =============================================================================
//   Author: K Perkins
//   Date:   Oct 5, 2013
//   Taken From: http://programmingnotes.org/
//   File:  Server.cpp
//   Description: Using a Hash Table, this program simulates a server and client 
//     application. The server program maintains a hash table of records and 
//     a pool of threads. The client requests records from the server by sending 
//     record ID's over the message queue. The server retrieves a request from 
//     the message queue and wakes up a thread in the thread pool. The awakened 
//     thread then uses the ID to retrieve the corresponding record from the 
//     hash table and sends the record to the client over the message queue.
//     
//     This is the server program which creates a message queue using the msgget() 
//     system call, checks the message queue for new messages using the msgrcv() 
//     system call, and uses the msgsnd system call to send messages back to 
//     the client
// =============================================================================
#include <iostream>
#include <vector>
#include <list>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <csignal>
#include <pthread.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>
using namespace std;

// Compile & Run
// g++ Server.cpp -o Server -lpthread
// ./Server <FILE NAME> <NUMBER OF THREADS>

// function prototypes
void SignalHandler(int arg);
void InsertInitialDataIntoTable(ifstream& infile);
void* SearchRecords(void* args);
void SendRecord(int id, const char* firstName, const char* lastName);
void* GenerateNewRecord(void* args);

// items which are placed inside the hash table cell
struct Record
{
    int id;
    char firstName[50];
    char lastName[50];
};

// cell for the hash table
struct Cell
{   
    list<Record> cell;
    pthread_mutex_t mutex;
};

// message queue structure
struct MsgQueue
{
    // the channel the connection will be on
    long messageType;
    int recordID;
    char recordName[100];	
};

// constant variables
const int HASH_TABLE_SIZE = 100;
const int NUM_NEW_RECORDS_THREADS = 5;
const int CLIENT_TO_SERVER_CHANNEL = 2;
const int SERVER_TO_CLIENT_CHANNEL = 4;	
const int MSG_Q_ID = 0664;

// global variables
int msqid = 0; // message queue ID
vector<Cell> hashTable(HASH_TABLE_SIZE);
list<int> recievedMsg;

int main(int argc, char* argv[])
{		
    // declare variables
    srand(time(NULL));
    signal(SIGINT, SignalHandler);	// override the CTRL-C terminal singal 
    ifstream infile; // used to read in the file
    int searchThreadNum = 0; // keep track of how many threads are being processed
    int newRecThreadNum = 0;
    int numSearchThreads = 0; // how many threads search the table for records   
    key_t key = 0; // generate key to a file
    pthread_t* searchRecordThreads = NULL; // array of search records threads
    pthread_t* getNewRecordThreads = NULL; // array of new records threads  
    MsgQueue msg;  // instantiate a message queue   
        
    // check if theres enough commandline args
    if(argc < 3)
    {
        cerr<<"n** ERROR NOT ENOUGH ARGS!nn"
            <<"USAGE: "<<argv[0]<<" <FILE NAME> <NUMBER OF THREADS>nn";
        exit(1);
    }

    // open the input records file
    infile.open(argv[1]);

    // check to see if file exists
    if(infile.fail())
    {
        cerr<<"n** ERROR: ""<<argv[1]<<"" could not be found!n";
        exit(1);
    }

    // insert data into the hash table from the source file
    InsertInitialDataIntoTable(infile);

    // close the file after we are done using it
    infile.close();
        
    // get the number of threads from the command line 
    numSearchThreads = atoi(argv[2]);

    // initialize the search thread array with the number 
    // specified from the commandline
    searchRecordThreads = new pthread_t[numSearchThreads];

    // initialize the new records thread array with the
    // specified number
    getNewRecordThreads = new pthread_t[NUM_NEW_RECORDS_THREADS];
        

    // get a key for our msg queue
    key = ftok("/bin/ls", 'O');

    // check if we got a valid key
    if(key < 0)
    {
        perror("ftok error");
        exit(1);
    }	

    // get a msg ID
    msqid = msgget(key, MSG_Q_ID | IPC_CREAT);	
        
    // check if we got a valid ID
    if(msqid < 0)
    {
        perror("msgget error");
        exit(1);	
    }

    cout<<"n** SERVER ID #"<<msqid<<" SUCCESSFULLY ESTABLISHEDn"<<endl;			

    // infinite loop to send/recieve messages to/from client			
    do{	
        // recieve record from client
        if(msgrcv(msqid, &msg, sizeof(msg) - sizeof(long), CLIENT_TO_SERVER_CHANNEL, 0) < 0)
        {
            perror("msgsnd error");
            exit(1);
        }            

        // save the recieved record from the client into a linked list
        // this is used in the "SearchRecords" function
        recievedMsg.push_back(msg.recordID);
	    
    // --- SEARCH RECORDS THREADS        
        // keep track of how many threads are being used 	        			    
        if(searchThreadNum > numSearchThreads-1)
        {
            searchThreadNum = 0;        
        }	

        // create threads & send them to work
        if(pthread_create(&searchRecordThreads[searchThreadNum], NULL, &SearchRecords, NULL) < 0)
        {
            perror("pthread_create error");
            exit(1);
        }       	         

        // wait for threads to finish
        pthread_join(searchRecordThreads[searchThreadNum], NULL);        
    
    // --- GENERATE NEW RECORDS THREADS
        // keep track of how many threads are being used 	        			    
        if(newRecThreadNum > NUM_NEW_RECORDS_THREADS-1)
        {
            newRecThreadNum = 0;        
        }	

        // create threads & send them to work
        if(pthread_create(&getNewRecordThreads[newRecThreadNum], NULL, &GenerateNewRecord, NULL) < 0)
        {
            perror("pthread_create error");
            exit(1);
        }       	         

        // wait for threads to finish
        pthread_join(getNewRecordThreads[newRecThreadNum], NULL); 
        
    // --- INCREMENT NUMBER OF THREADS BEING USED       
        //cout<<searchThreadNum<<endl;
        ++searchThreadNum;  
        ++newRecThreadNum;     
    }while(true);							 
            
    return 0;
}// end of main

void* GenerateNewRecord(void* args)
{	
    const char* names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",
        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",
        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",
        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",
        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",
        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",
        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",
        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",
        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",
        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",
        "Kenneth","Perkins","Kaleena"};
        
    Record temp;
    int record = rand()%10000;        
    int nameLen = sizeof(names)/sizeof(names[0]);  

    // lock the current hash table cell
    if(pthread_mutex_lock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
    {
        perror("pthread_mutex_lock error");
        exit(1);
    }    

    // put the new data into the hash table
    temp.id = record;
    strncpy(temp.firstName, names[rand()%(nameLen-1)], sizeof(temp.firstName));
    strncpy(temp.lastName, names[rand()%(nameLen-1)], sizeof(temp.lastName));

    hashTable[record%HASH_TABLE_SIZE].cell.push_back(temp);
    pthread_mutex_init(&hashTable[temp.id%HASH_TABLE_SIZE].mutex, NULL);
        
    // unlock the current hash table cell
    if(pthread_mutex_unlock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
    {
        perror("pthread_mutex_lock error");
        exit(1);
    }
    return 0;	
}// end of GenerateNewRecord

void* SearchRecords(void* args)
{	
    int record = 0;
    bool found = false;

    // get the record from the client to search the hash table
    if(!recievedMsg.empty())
    {
        record = recievedMsg.front();
        recievedMsg.pop_front();
    }
    //cout<<endl<<record<<endl;

    // if the current hash table cell isnt empty, search for the record id
    if(!hashTable[record%HASH_TABLE_SIZE].cell.empty())
    {   
        // lock the current hash table cell
        if(pthread_mutex_lock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
        {
            perror("pthread_mutex_lock error");
            exit(1);
        }
        
        // search hash table cell to see if given record is there
        for(list<Record>::iterator iter = hashTable[record%HASH_TABLE_SIZE].cell.begin(); 
            iter != hashTable[record%HASH_TABLE_SIZE].cell.end(); ++iter)
        {
            // we found a match in the hash table
            if(iter->id == record)
            {
                // set the data fields of the found record 
                // to prepare it to be sent over the message queue                
                SendRecord(iter->id, iter->firstName, iter->lastName);
                found = true;
                break;
            }
        }

        // unlock the current hash table cell	
        if(pthread_mutex_unlock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
        {
            perror("pthread_mutex_lock error");
            exit(1);
        }
    }

    // if we didnt find a record, tell that to the client
    if(!found)
    {
        SendRecord(-1, "Record Not Found!", "");
    }
    return 0;	
}// end of SearchRecords

void SendRecord(int id, const char* firstName, const char* lastName)
{
    MsgQueue msg;  // instantiate a message queue

    // set the message queue channel
    msg.messageType = SERVER_TO_CLIENT_CHANNEL;	    

    // set the record id
    msg.recordID = id;                

    // set the record name
    strncpy(msg.recordName, firstName, sizeof(msg.recordName));
    strncat(msg.recordName, " ", sizeof(msg.recordName));
    strncat(msg.recordName, lastName, sizeof(msg.recordName));        	

    // send record to client
    if(msgsnd(msqid, &msg, sizeof(msg) - sizeof(long), 0) < 0)
    {
        perror("msgsnd error");
        exit(1);
    }    
}// end of SendRecord   

void InsertInitialDataIntoTable(ifstream& infile)
{  
    Record temp;
    while(infile>>temp.id >>temp.firstName >>temp.lastName)
    {
        hashTable[temp.id%HASH_TABLE_SIZE].cell.push_back(temp);
        pthread_mutex_init(&hashTable[temp.id%HASH_TABLE_SIZE].mutex, NULL);
    }   
}// end of InsertInitialDataIntoTable

void SignalHandler(int arg)
{
    cerr<<"nnCaught the CTRL-Cn"
        <<"Shutting down the server connection..n";			

    // deallocate the queue 
    if(msgctl(msqid, IPC_RMID, NULL) < 0)
    {
        perror("msgctl error");
    }	 		
    exit(0);
}// http://programmingnotes.org/
			
				
					
				
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						// =============================================================================
//   Author: K Perkins
//   Date:   Oct 5, 2013
//   Taken From: http://programmingnotes.org/
//   File:  Server.cpp
//   Description: Using a Hash Table, this program simulates a server and client 
//     application. The server program maintains a hash table of records and 
//     a pool of threads. The client requests records from the server by sending 
//     record ID's over the message queue. The server retrieves a request from 
//     the message queue and wakes up a thread in the thread pool. The awakened 
//     thread then uses the ID to retrieve the corresponding record from the 
//     hash table and sends the record to the client over the message queue.
//     
//     This is the server program which creates a message queue using the msgget() 
//     system call, checks the message queue for new messages using the msgrcv() 
//     system call, and uses the msgsnd system call to send messages back to 
//     the client
// =============================================================================
#include <iostream>
#include <vector>
#include <list>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <csignal>
#include <pthread.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>
using namespace std;
 
// Compile & Run
// g++ Server.cpp -o Server -lpthread
// ./Server <FILE NAME> <NUMBER OF THREADS>
 
// function prototypes
void SignalHandler(int arg);
void InsertInitialDataIntoTable(ifstream& infile);
void* SearchRecords(void* args);
void SendRecord(int id, const char* firstName, const char* lastName);
void* GenerateNewRecord(void* args);
 
// items which are placed inside the hash table cell
struct Record
{
    int id;
    char firstName[50];
    char lastName[50];
};
 
// cell for the hash table
struct Cell
{   
    list<Record> cell;
    pthread_mutex_t mutex;
};
 
// message queue structure
struct MsgQueue
{
    // the channel the connection will be on
    long messageType;
    int recordID;
    char recordName[100];	
};
 
// constant variables
const int HASH_TABLE_SIZE = 100;
const int NUM_NEW_RECORDS_THREADS = 5;
const int CLIENT_TO_SERVER_CHANNEL = 2;
const int SERVER_TO_CLIENT_CHANNEL = 4;	
const int MSG_Q_ID = 0664;
 
// global variables
int msqid = 0; // message queue ID
vector<Cell> hashTable(HASH_TABLE_SIZE);
list<int> recievedMsg;
 
int main(int argc, char* argv[])
{		
    // declare variables
    srand(time(NULL));
    signal(SIGINT, SignalHandler);	// override the CTRL-C terminal singal 
    ifstream infile; // used to read in the file
    int searchThreadNum = 0; // keep track of how many threads are being processed
    int newRecThreadNum = 0;
    int numSearchThreads = 0; // how many threads search the table for records   
    key_t key = 0; // generate key to a file
    pthread_t* searchRecordThreads = NULL; // array of search records threads
    pthread_t* getNewRecordThreads = NULL; // array of new records threads  
    MsgQueue msg;  // instantiate a message queue   
        
    // check if theres enough commandline args
    if(argc < 3)
    {
        cerr<<"n** ERROR NOT ENOUGH ARGS!nn"
            <<"USAGE: "<<argv[0]<<" <FILE NAME> <NUMBER OF THREADS>nn";
        exit(1);
    }
 
    // open the input records file
    infile.open(argv[1]);
 
    // check to see if file exists
    if(infile.fail())
    {
        cerr<<"n** ERROR: ""<<argv[1]<<"" could not be found!n";
        exit(1);
    }
 
    // insert data into the hash table from the source file
    InsertInitialDataIntoTable(infile);
 
    // close the file after we are done using it
    infile.close();
        
    // get the number of threads from the command line 
    numSearchThreads = atoi(argv[2]);
 
    // initialize the search thread array with the number 
    // specified from the commandline
    searchRecordThreads = new pthread_t[numSearchThreads];
 
    // initialize the new records thread array with the
    // specified number
    getNewRecordThreads = new pthread_t[NUM_NEW_RECORDS_THREADS];
        
 
    // get a key for our msg queue
    key = ftok("/bin/ls", 'O');
 
    // check if we got a valid key
    if(key < 0)
    {
        perror("ftok error");
        exit(1);
    }	
 
    // get a msg ID
    msqid = msgget(key, MSG_Q_ID | IPC_CREAT);	
        
    // check if we got a valid ID
    if(msqid < 0)
    {
        perror("msgget error");
        exit(1);	
    }
 
    cout<<"n** SERVER ID #"<<msqid<<" SUCCESSFULLY ESTABLISHEDn"<<endl;			
 
    // infinite loop to send/recieve messages to/from client			
    do{	
        // recieve record from client
        if(msgrcv(msqid, &msg, sizeof(msg) - sizeof(long), CLIENT_TO_SERVER_CHANNEL, 0) < 0)
        {
            perror("msgsnd error");
            exit(1);
        }            
 
        // save the recieved record from the client into a linked list
        // this is used in the "SearchRecords" function
        recievedMsg.push_back(msg.recordID);
	    
    // --- SEARCH RECORDS THREADS        
        // keep track of how many threads are being used 	        			    
        if(searchThreadNum > numSearchThreads-1)
        {
            searchThreadNum = 0;        
        }	
 
        // create threads & send them to work
        if(pthread_create(&searchRecordThreads[searchThreadNum], NULL, &SearchRecords, NULL) < 0)
        {
            perror("pthread_create error");
            exit(1);
        }       	         
 
        // wait for threads to finish
        pthread_join(searchRecordThreads[searchThreadNum], NULL);        
    
    // --- GENERATE NEW RECORDS THREADS
        // keep track of how many threads are being used 	        			    
        if(newRecThreadNum > NUM_NEW_RECORDS_THREADS-1)
        {
            newRecThreadNum = 0;        
        }	
 
        // create threads & send them to work
        if(pthread_create(&getNewRecordThreads[newRecThreadNum], NULL, &GenerateNewRecord, NULL) < 0)
        {
            perror("pthread_create error");
            exit(1);
        }       	         
 
        // wait for threads to finish
        pthread_join(getNewRecordThreads[newRecThreadNum], NULL); 
        
    // --- INCREMENT NUMBER OF THREADS BEING USED       
        //cout<<searchThreadNum<<endl;
        ++searchThreadNum;  
        ++newRecThreadNum;     
    }while(true);							 
            
    return 0;
}// end of main
 
void* GenerateNewRecord(void* args)
{	
    const char* names[]={"Alva","Edda","Hiram","Lemuel","Della","Roseann","Sang",
        "Evelia","Claire","Marylou","Magda","Irvin","Reagan","Deb","Hillary",
        "Tuyetm","Cherilyn","Amina","Justin","Neville","Jessica","Demi",
        "Graham","Cinderella","Freddy","Vivan","Marjorie","Krystal","Liza",
        "Spencer","Jordon","Bernie","Geraldine","Kati","Jetta","Carmella",
        "Chery","Earlene","Gene","Lorri","Albertina","Ula","Karena","Johanna",
        "Alex","Tobias","Lashawna","Domitila","Chantel","Deneen","Nigel",
        "Lashanda","Donn","Theda","Many","Jeramy","Jodee","Tamra","Dessie",
        "Lawrence","Jaime","Basil","Roger","Cythia","Homer","Lilliam","Victoria",
        "Tod","Harley","Meghann","Jacquelyne","Arie","Rosemarie","Lyndon","Blanch",
        "Kenneth","Perkins","Kaleena"};
        
    Record temp;
    int record = rand()%10000;        
    int nameLen = sizeof(names)/sizeof(names[0]);  
 
    // lock the current hash table cell
    if(pthread_mutex_lock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
    {
        perror("pthread_mutex_lock error");
        exit(1);
    }    
 
    // put the new data into the hash table
    temp.id = record;
    strncpy(temp.firstName, names[rand()%(nameLen-1)], sizeof(temp.firstName));
    strncpy(temp.lastName, names[rand()%(nameLen-1)], sizeof(temp.lastName));
 
    hashTable[record%HASH_TABLE_SIZE].cell.push_back(temp);
    pthread_mutex_init(&hashTable[temp.id%HASH_TABLE_SIZE].mutex, NULL);
        
    // unlock the current hash table cell
    if(pthread_mutex_unlock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
    {
        perror("pthread_mutex_lock error");
        exit(1);
    }
    return 0;	
}// end of GenerateNewRecord
 
void* SearchRecords(void* args)
{	
    int record = 0;
    bool found = false;
 
    // get the record from the client to search the hash table
    if(!recievedMsg.empty())
    {
        record = recievedMsg.front();
        recievedMsg.pop_front();
    }
    //cout<<endl<<record<<endl;
 
    // if the current hash table cell isnt empty, search for the record id
    if(!hashTable[record%HASH_TABLE_SIZE].cell.empty())
    {   
        // lock the current hash table cell
        if(pthread_mutex_lock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
        {
            perror("pthread_mutex_lock error");
            exit(1);
        }
        
        // search hash table cell to see if given record is there
        for(list<Record>::iterator iter = hashTable[record%HASH_TABLE_SIZE].cell.begin(); 
            iter != hashTable[record%HASH_TABLE_SIZE].cell.end(); ++iter)
        {
            // we found a match in the hash table
            if(iter->id == record)
            {
                // set the data fields of the found record 
                // to prepare it to be sent over the message queue                
                SendRecord(iter->id, iter->firstName, iter->lastName);
                found = true;
                break;
            }
        }
 
        // unlock the current hash table cell	
        if(pthread_mutex_unlock(&hashTable[record%HASH_TABLE_SIZE].mutex) < 0)
        {
            perror("pthread_mutex_lock error");
            exit(1);
        }
    }
 
    // if we didnt find a record, tell that to the client
    if(!found)
    {
        SendRecord(-1, "Record Not Found!", "");
    }
    return 0;	
}// end of SearchRecords
 
void SendRecord(int id, const char* firstName, const char* lastName)
{
    MsgQueue msg;  // instantiate a message queue
 
    // set the message queue channel
    msg.messageType = SERVER_TO_CLIENT_CHANNEL;	    
 
    // set the record id
    msg.recordID = id;                
 
    // set the record name
    strncpy(msg.recordName, firstName, sizeof(msg.recordName));
    strncat(msg.recordName, " ", sizeof(msg.recordName));
    strncat(msg.recordName, lastName, sizeof(msg.recordName));        	
 
    // send record to client
    if(msgsnd(msqid, &msg, sizeof(msg) - sizeof(long), 0) < 0)
    {
        perror("msgsnd error");
        exit(1);
    }    
}// end of SendRecord   
 
void InsertInitialDataIntoTable(ifstream& infile)
{  
    Record temp;
    while(infile>>temp.id >>temp.firstName >>temp.lastName)
    {
        hashTable[temp.id%HASH_TABLE_SIZE].cell.push_back(temp);
        pthread_mutex_init(&hashTable[temp.id%HASH_TABLE_SIZE].mutex, NULL);
    }   
}// end of InsertInitialDataIntoTable
 
void SignalHandler(int arg)
{
    cerr<<"nnCaught the CTRL-Cn"
        <<"Shutting down the server connection..n";			
 
    // deallocate the queue 
    if(msgctl(msqid, IPC_RMID, NULL) < 0)
    {
        perror("msgctl error");
    }	 		
    exit(0);
}// http://programmingnotes.org/

The client program has a much easier flow of control. It is implemented below.

==== 4. CLIENT ====

The client has the following structure and function:

Multi Threaded Process Client Flow Control	Select Show
1. The client program connects to the message queue previously established by the server. 2. If the connection is successful, then the client goes into an infinite loop where it: • Generates a random id between 0 and 10000. • Sends the id to the server via the message queue. • Waits for the server to reply with the requested record. • Displays the record received. • Repeats the process.

Multi Threaded Process Client Flow Control

Select Show

The client program was designed to sleep for 1 second every time a new record is obtained from the server. This makes it so its easier for the user to see what is being displayed on the screen.

The client program is invoked with the following commandline structure:

./client

The client is implemented below.



		
		
			Multi Threaded Process Server With Hash Table
			
C++
			
			// =============================================================================
//   Author: K Perkins
//   Date:   Oct 5, 2013
//   Taken From: http://programmingnotes.org/
//   File:  Client.cpp
//   Description: Using a Hash Table, this program simulates a server and client 
//     application. The server program maintains a hash table of records and 
//     a pool of threads. The client requests records from the server by sending 
//     record ID's over the message queue. The server retrieves a request from 
//     the message queue and wakes up a thread in the thread pool. The awakened 
//     thread then uses the ID to retrieve the corresponding record from the 
//     hash table and sends the record to the client over the message queue.
//     
//     This is the client program which connects to the message queue that the 
//     server previously establishes using the msgget() system call. It checks 
//     the message queue for sucessfully found records using the msgrcv() system 
//     call, and uses the msgsnd system call to send new search records back to 
//     the server, where it searches for new records
// 
//     NOTE: This file is set to display records on a 1 second delay
// =============================================================================
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
using namespace std;

// Compile & Run
// g++ Client.cpp -o Client
// ./Client

// message queue structure
struct MsgQueue
{
    // the channel the connection will be on
	long messageType;
	int recordID;
	char recordName[100];	
};

// constant variables
const int HOW_LONG_TO_SLEEP = 1;
const int CLIENT_TO_SERVER_CHANNEL = 2;
const int SERVER_TO_CLIENT_CHANNEL = 4;
const int MSG_Q_ID = 0664;

int main()
{
    // declare variables
    MsgQueue msg;
    srand(time(NULL));
    key_t key = 0;
    int msqid = 0; // message queue ID
        
    // get a key for the queue
    key = ftok("/bin/ls", 'O');

    // check if we got a valid key
    if(key < 0)
    {
        cerr<<"ftok";
        exit(1);
    }	

    // get the ID of the queue	
    msqid = msgget(key,MSG_Q_ID);	

    // check if we got a valid ID
    if(msqid < 0)
    {
        cerr<<"n** ERROR - CONNECTION TO SERVER NOT FOUNDnn";
        exit(1);	
    }	

    cerr<<"n** CONNECTION TO SERVER ID #"<<msqid<<" SUCCESSn"<<endl;	

    // infinite loop to send/recieve messages from server			
    do{	    
        // connect to the server
        msg.messageType = CLIENT_TO_SERVER_CHANNEL;

        // generate a random search key
        msg.recordID = rand()%10000;
        
        // send record search to the server
        if(msgsnd(msqid, &msg, sizeof(msg) - sizeof(long), 0) < 0)
        {
            cerr<<"n** SERVER CONNECTION CLOSED..nn";
            exit(1);
        }
        
        // recieve a record from the server
        if(msgrcv(msqid, &msg, sizeof(msg) - sizeof(long), SERVER_TO_CLIENT_CHANNEL, 0) < 0)
        {
            cerr<<"n** SERVER CONNECTION CLOSED..nn";
            exit(1);
        }
        
        // if we found a valid record, display it to the screen
        if(msg.recordID > 0)
        {
            cerr<< "ID = "<<msg.recordID<<"  tRecord = "<<msg.recordName<<endl;
            sleep(HOW_LONG_TO_SLEEP);
        }        			    		    
    }while(true);    

    return 0;
}// http://programmingnotes.org/
			
				
					
				
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						// =============================================================================
//   Author: K Perkins
//   Date:   Oct 5, 2013
//   Taken From: http://programmingnotes.org/
//   File:  Client.cpp
//   Description: Using a Hash Table, this program simulates a server and client 
//     application. The server program maintains a hash table of records and 
//     a pool of threads. The client requests records from the server by sending 
//     record ID's over the message queue. The server retrieves a request from 
//     the message queue and wakes up a thread in the thread pool. The awakened 
//     thread then uses the ID to retrieve the corresponding record from the 
//     hash table and sends the record to the client over the message queue.
//     
//     This is the client program which connects to the message queue that the 
//     server previously establishes using the msgget() system call. It checks 
//     the message queue for sucessfully found records using the msgrcv() system 
//     call, and uses the msgsnd system call to send new search records back to 
//     the server, where it searches for new records
// 
//     NOTE: This file is set to display records on a 1 second delay
// =============================================================================
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
using namespace std;
 
// Compile & Run
// g++ Client.cpp -o Client
// ./Client
 
// message queue structure
struct MsgQueue
{
    // the channel the connection will be on
	long messageType;
	int recordID;
	char recordName[100];	
};
 
// constant variables
const int HOW_LONG_TO_SLEEP = 1;
const int CLIENT_TO_SERVER_CHANNEL = 2;
const int SERVER_TO_CLIENT_CHANNEL = 4;
const int MSG_Q_ID = 0664;
 
int main()
{
    // declare variables
    MsgQueue msg;
    srand(time(NULL));
    key_t key = 0;
    int msqid = 0; // message queue ID
        
    // get a key for the queue
    key = ftok("/bin/ls", 'O');
 
    // check if we got a valid key
    if(key < 0)
    {
        cerr<<"ftok";
        exit(1);
    }	
 
    // get the ID of the queue	
    msqid = msgget(key,MSG_Q_ID);	
 
    // check if we got a valid ID
    if(msqid < 0)
    {
        cerr<<"n** ERROR - CONNECTION TO SERVER NOT FOUNDnn";
        exit(1);	
    }	
 
    cerr<<"n** CONNECTION TO SERVER ID #"<<msqid<<" SUCCESSn"<<endl;	
 
    // infinite loop to send/recieve messages from server			
    do{	    
        // connect to the server
        msg.messageType = CLIENT_TO_SERVER_CHANNEL;
 
        // generate a random search key
        msg.recordID = rand()%10000;
        
        // send record search to the server
        if(msgsnd(msqid, &msg, sizeof(msg) - sizeof(long), 0) < 0)
        {
            cerr<<"n** SERVER CONNECTION CLOSED..nn";
            exit(1);
        }
        
        // recieve a record from the server
        if(msgrcv(msqid, &msg, sizeof(msg) - sizeof(long), SERVER_TO_CLIENT_CHANNEL, 0) < 0)
        {
            cerr<<"n** SERVER CONNECTION CLOSED..nn";
            exit(1);
        }
        
        // if we found a valid record, display it to the screen
        if(msg.recordID > 0)
        {
            cerr<< "ID = "<<msg.recordID<<"  tRecord = "<<msg.recordName<<endl;
            sleep(HOW_LONG_TO_SLEEP);
        }        			    		    
    }while(true);    
 
    return 0;
}// http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

See sample files named server.cpp and client.cpp which illustrate interprocess communications using message queues. See file condvar.cpp which illustrates the use of condition variables. Finally, see file signal.cpp which illustrates the overriding of default signal handlers.

The following is sample output:
(Note: remember to include the initial records input file!)

SERVER OUTPUT:

./Server INPUT_Records_programmingnotes_freeweq_com.txt 26
** SERVER ID #1015808 SUCCESSFULLY ESTABLISHED ^C
Caught the CTRL-C Shutting down the server connection..

CLIENT OUTPUT:

./Client
** CONNECTION TO SERVER ID #1015808 SUCCESS ID = 243 Record = Graham Basil ID = 7943 Record = Tobias Arie ID = 3607 Record = Claire Amina ID = 849 Record = Jetta Victoria ID = 126 Record = Jeramy Tod ID = 7483 Record = Vivan Krystal ID = 8036 Record = Lilliam Harley ID = 1901 Record = Kati Basil ID = 3524 Record = Kenneth Perkins ID = 5256 Record = Jodee Albertina ID = 7065 Record = Marylou Donn ID = 3951 Record = Ula Domitila ID = 395 Record = Jaime Lilliam ID = 9234 Record = Nigel Gene ID = 4148 Record = Carmella Evelia ID = 9340 Record = Sang Cherilyn ID = 3834 Record = Jessica Freddy
** SERVER CONNECTION CLOSED..

C++ || Custom Template Hash Map With Iterator Using Separate Chaining

June 11, 2013 admin No comments

Before we get into the code, what is a Hash Map? Simply put, a Hash Map is an extension of a Hash Table; which is a data structure used to map unique “keys” to specific “values.” The Hash Map demonstrated on this page is different from the previous Hash Table implementation in that key/value pairs do not need to be the same datatype, they can be completely different. So for example, if you wish to map a string “key” to an integer “value“, utilizing a Hash Map is ideal.

In its most simplest form, a Hash Map can be thought of as an associative array, or a “dictionary.” Hash Map’s are composed of a collection of key/value pairs, such that each possible key appears atleast once in the collection for a given value. While a standard array requires that indice subscripts be integers, a hash map can use a string, an integer, or even a floating point value as the index. That index is called the “key,” and the contents within the array at that specific index location is called the “value.” A hash map uses a hash function to generate an index into the table, creating buckets or slots, from which the correct value can be found.

To illustrate, suppose that you’re working with some data that has values associated with strings — for instance, you might have student names and you wish to assign them grades. How would you store this data? Depending on your skill level, you might use multiple arrays during the implementation. For example, in terms of a one dimensional array, if we wanted to access the data for a student located at index #25, we could access it by doing:

studentNames[25]; // do something with the data studentGrades[25];

Here, we dont have to search through each element in the array to find what we need, we just access it at index #25. The question is, how do we know that index #25 holds the data that we are looking for? If we have a large set of data, not only will keeping track of multiple arrays become tiresome, but doing a sequential search over each item within the separate arrays can become very inefficient. That is where hashing comes in handy. Using a Hash Map, we can use the students name as the “key,” and the students grade as the data “value.” Given this “key” (the students name), we can apply a hash function to map a unique index or bucket within the hash table to find the data “value” (the students grade) that we wish to access.

So in essence, a Hash Map is an extension of a hash table, which is a data structure that stores key/value pairs. Hash tables are typically used because they are ideal for doing a quick search of items.

Though hashing is ideal, it isnt perfect. It is possible for multiple “keys” to be hashed into the same location. Hash “collisions” are practically unavoidable when hashing large data sets. The code demonstrated on this page handles collisions via separate chaining, utilizing an array of linked list head nodes to store multiple keys within one bucket – should any collisions occur.

A special feature of this current hash map class is that its implemented as a multimap, meaning that more than one “value” can be associated with a given “key.” For example, in a student enrollment system where students may be enrolled in multiple classes simultaneously, there might be an association for each enrollment where the “key” is the student ID, and the “value” is the course ID. In this example, if a given student is enrolled in three courses, there will be three associated “values” (course ID’s) for one “key” (student ID) in the Hash Map.

An iterator was also implemented, making data access that much more simple within the hash map class. Click here for an overview demonstrating how custom iterators can be built.

=== CUSTOM TEMPLATE HASH MAP WITH ITERATOR ===



		
		
			#include 'HashMap.h' - Hash Map With Iterator
			
C++
			
			// ============================================================================
//    Author: Kenneth Perkins
//    Date:   June 11, 2013
//    Taken From: http://programmingnotes.org/
//    File:  HashMap.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a Hash Map.
// ============================================================================
#ifndef TEMPLATE_HASH_MAP
#define TEMPLATE_HASH_MAP
#include <iostream>
#include <string>
#include <sstream>
#include <cstdlib>

// if user doesnt define, this is the
// default hash map size
const int HASH_SIZE = 350;

template <class Key, class Value>
class HashMap
{
public:
    HashMap(int hashSze = HASH_SIZE);
        /*   Function: Constructor initializes hash map
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty(int keyIndex);
        /*   Function: Determines whether hash map is empty at the given hash
                            map key index
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is empty and the
                             function = false if hash map is not empty */
    bool  IsFull();
        /*   Function: Determines whether hash map is full
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is full and the
                             function = false if hash map is not full */
    int Hash(Key m_key);
        /*   Function: Computes and returns a hash map key index for a given item
                        The returned key index is the given cell where the item resides
            Precondition:  Hash map has been created and is not full
            Postcondition: The hash key is returned */
    void Insert(Key m_key, Value m_value);
        /*   Function: Adds new item to the back of the list at a given key in the hash map
                         A unique hash key is automatically generated for each new item
            Precondition:  Hash map has been created and is not full
            Postcondition: Item is in the hash map */
    bool Remove(Key m_key, Value deleteItem);
        /*   Function: Removes the first instance from the map whose value is "deleteItem"
            Precondition:  Hash map has been created and is not empty
            Postcondition: The function = true if deleteItem is found and the
                             function = false if deleteItem is not found */
    void Sort(int keyIndex);
        /*   Function: Sort the items in the map at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The hash map is sorted */
    int TableSize();
        /*   Function: Return the size of the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int TotalElems();
        /*   Function: Return the total number of elements contained in the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int BucketSize(int keyIndex);
        /*   Function: Return the number of items contained in the hash map
                        cell at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The size of the given key cell is returned */
    int Count(Key m_key, Value searchItem);
        /*   Function: Return the number of times searchItem appears in the map
                        at the given key
            Precondition: Hash map has been initialized
            Postcondition: The number of times searchItem appears in the map is returned */
    int ContainsKey(Key m_key);
        /*   Function: Return the number of times the given key appears in the hashmap
            Precondition: Hash map has been initialized
            Postcondition: The number of times the given key appears in the map is returned */
    void MakeEmpty();
        /*   Function: Initializes hash map to an empty state
            Precondition: Hash map has been created
            Postcondition: Hash map no longer exists */
    ~HashMap();
        /*   Function: Removes the hash map
            Precondition: Hash map has been declared
            Postcondition: Hash map no longer exists */

    //  -- ITERATOR CLASS --
    class Iterator;
        /*   Function: Class declaration to the iterator
            Precondition: Hash map has been declared
            Postcondition: Hash Iterator has been declared */

    Iterator begin(int keyIndex){return(!IsEmpty(keyIndex)) ? head[keyIndex]:NULL;}
        /*   Function: Returns the beginning of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */

    Iterator end(int keyIndex=0){return NULL;}
        /*   Function: Returns the end of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */

private:
    struct KeyValue  // struct to hold key/value pairs
    {
        Key key;
        Value value;
    };
    struct node
    {
        KeyValue currentItem;
        node* next;
    };
    node** head; // array of linked list declaration - front of each hash map cell
    int hashSize; // the size of the hash map (how many cells it has)
    int totElems; // holds the total number of elements in the entire table
    int* bucketSize; // holds the total number of elems in each specific hash map cell
};

//=========================  Implementation  ================================//

template <class Key, class Value>
HashMap<Key, Value>::HashMap(int hashSze)
{
    hashSize = hashSze;
    head = new node*[hashSize];
    bucketSize = new int[hashSize];
    for(int x=0; x < hashSize; ++x)
    {
        head[x] = NULL;
        bucketSize[x] = 0;
    }
    totElems = 0;
}/* End of HashMap */

template <class Key, class Value>
bool HashMap<Key, Value>::IsEmpty(int keyIndex)
{
    if(keyIndex >=0 && keyIndex < hashSize)
    {
        return head[keyIndex] == NULL;
    }
    return true;
}/* End of IsEmpty */

template <class Key, class Value>
bool HashMap<Key, Value>::IsFull()
{
    try
    {
        node* location = new node;
        delete location;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}/* End of IsFull */

template <class Key, class Value>
int HashMap<Key, Value>::Hash(Key m_key)
{
    long h = 19937;
    std::stringstream convert;

    // convert the parameter to a string using "stringstream" which is done
    // so we can hash multiple datatypes using only one function
    convert << m_key;
    std::string temp = convert.str();

    for(unsigned x=0; x < temp.length(); ++x)
    {
        h = (h << 6) ^ (h >> 26) ^ temp[x];
    }
    return abs(h % hashSize);
} /* End of Hash */

template <class Key, class Value>
void HashMap<Key, Value>::Insert(Key m_key, Value m_value)
{
    if(IsFull())
    {
        //std::cout<<"\nINSERT ERROR - HASH MAP FULL\n";
    }
    else
    {
        int keyIndex = Hash(m_key);
        node* newNode = new node;   // add new node
        newNode-> currentItem.key = m_key;
        newNode-> currentItem.value = m_value;
        newNode-> next = NULL;

        if(IsEmpty(keyIndex))
        {
            head[keyIndex] = newNode;
        }
        else
        {
            node* temp = head[keyIndex];
            while(temp-> next != NULL)
            {
                temp = temp-> next;
            }
            temp-> next = newNode;
        }
        ++bucketSize[keyIndex];
        ++totElems;
    }
}/* End of Insert */

template <class Key, class Value>
bool HashMap<Key, Value>::Remove(Key m_key, Value deleteItem)
{
    bool isFound = false;
    node* temp;
    int keyIndex = Hash(m_key);

    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nREMOVE ERROR - HASH MAP EMPTY\n";
    }
    else if(head[keyIndex]->currentItem.key == m_key
            && head[keyIndex]->currentItem.value == deleteItem)
    {
        temp = head[keyIndex];
        head[keyIndex] = head[keyIndex]-> next;
        delete temp;
        --totElems;
        --bucketSize[keyIndex];
        isFound = true;
    }
    else
    {
        for(temp = head[keyIndex];temp->next!=NULL;temp=temp->next)
        {
            if(temp->next->currentItem.key == m_key
                && temp->next->currentItem.value == deleteItem)
            {
                node* deleteNode = temp->next;
                temp-> next = temp-> next-> next;
                delete deleteNode;
                isFound = true;
                --totElems;
                --bucketSize[keyIndex];
                break;
            }
        }
    }
    return isFound;
}/* End of Remove */

template <class Key, class Value>
void HashMap<Key, Value>::Sort(int keyIndex)
{
    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nSORT ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        int listSize = BucketSize(keyIndex);
        bool sorted = false;

        do{
            sorted = true;
            int x = 0;
            for(node* temp = head[keyIndex];
                temp->next!=NULL && x < listSize-1;
                temp=temp->next,++x)
            {
                if(temp-> currentItem.value > temp->next->currentItem.value)
                {
                    std::swap(temp-> currentItem,temp->next->currentItem);
                    sorted = false;
                }
            }
            --listSize;
        }while(!sorted);
    }
}/* End of Sort */

template <class Key, class Value>
int HashMap<Key, Value>::TableSize()
{
    return hashSize;
}/* End of TableSize */

template <class Key, class Value>
int HashMap<Key, Value>::TotalElems()
{
    return totElems;
}/* End of TotalElems */

template <class Key, class Value>
int HashMap<Key, Value>::BucketSize(int keyIndex)
{
    return(!IsEmpty(keyIndex)) ? bucketSize[keyIndex]:0;
}/* End of BucketSize */

template <class Key, class Value>
int HashMap<Key, Value>::Count(Key m_key, Value searchItem)
{
    int keyIndex = Hash(m_key);
    int search = 0;

    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nCOUNT ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)
        {
            if(temp->currentItem.key == m_key
                && temp->currentItem.value == searchItem)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of Count */

template <class Key, class Value>
int HashMap<Key, Value>::ContainsKey(Key m_key)
{
    int keyIndex = Hash(m_key);
    int search = 0;

    if(IsEmpty(keyIndex))
    {
        //std::cout<<"\nCONTAINS KEY ERROR - HASH MAP EMPTY\n";
    }
    else
    {
        for(node* temp = head[keyIndex];temp!=NULL;temp=temp->next)
        {
            if(temp->currentItem.key == m_key)
            {
                ++search;
            }
        }
    }
    return search;
}/* End of ContainsKey */

template <class Key, class Value>
void HashMap<Key, Value>::MakeEmpty()
{
    totElems = 0;
    for(int x=0; x < hashSize; ++x)
    {
        if(!IsEmpty(x))
        {
            //std::cout << "Destroying nodes ...\n";
            while(!IsEmpty(x))
            {
                node* temp = head[x];
                //std::cout << temp-> currentItem.value <<std::endl;
                head[x] = head[x]-> next;
                delete temp;
            }
        }
        bucketSize[x] = 0;
    }
}/* End of MakeEmpty */

template <class Key, class Value>
HashMap<Key, Value>::~HashMap()
{
    MakeEmpty();
    delete[] head;
    delete[] bucketSize;
}/* End of ~HashMap */

//   END OF THE HASH MAP CLASS
// -----------------------------------------------------------
//   START OF THE HASH MAP ITERATOR CLASS

template <class Key, class Value>
class HashMap<Key, Value>::Iterator :
        public std::iterator<std::forward_iterator_tag,Value>,
        public HashMap<Key, Value>
    {
public:
    // Iterator constructor
    Iterator(node* otherIter = NULL)
    {
        itHead = otherIter;
    }
    ~Iterator() {}
    // The assignment and relational operators are straightforward
    Iterator& operator=(const Iterator& other)
    {
        itHead = other.itHead;
        return(*this);
    }
    bool operator==(const Iterator& other)const
    {
        return itHead == other.itHead;
    }
    bool operator!=(const Iterator& other)const
    {
        return itHead != other.itHead;
    }
    bool operator<(const Iterator& other)const
    {
        return itHead < other.itHead;
    }
    bool operator>(const Iterator& other)const
    {
        return other.itHead < itHead;
    }
    bool operator<=(const Iterator& other)const
    {
        return (!(other.itHead < itHead));
    }
    bool operator>=(const Iterator& other)const
    {
        return (!(itHead < other.itHead));
    }
    // Update my state such that I refer to the next element in the
    // HashMap.
    Iterator operator+(int incr)
    {
        node* temp = itHead;
        for(int x=0; x < incr && temp!= NULL; ++x)
        {
            temp = temp->next;
        }
        return temp;
    }
    Iterator operator+=(int incr)
    {
        for(int x=0; x < incr && itHead!= NULL; ++x)
        {
            itHead = itHead->next;
        }
        return itHead;
    }
    Iterator& operator++() // pre increment
    {
        if(itHead != NULL)
        {
            itHead = itHead->next;
        }
        return(*this);
    }
    Iterator operator++(int) // post increment
    {
        node* temp = itHead;
        this->operator++();
        return temp;
    }
    KeyValue& operator[](int incr)
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL || (*this + incr) == NULL)
        {
            return junk;
        }
        return(*(*this + incr));
    }
    // Return a reference to the value in the node.  I do this instead
    // of returning by value so a caller can update the value in the
    // node directly.
    KeyValue& operator*()
    {
        // Return "junk" data
        // to prevent the program from crashing
        if(itHead == NULL)
        {
            return junk;
        }
        return itHead->currentItem;
    }
    KeyValue* operator->()
    {
        return(&**this);
    }
private:
    node* itHead;
    KeyValue junk;
};
#endif // http://programmingnotes.org/
			
				
					
				
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						// ============================================================================
//    Author: Kenneth Perkins
//    Date:   June 11, 2013
//    Taken From: http://programmingnotes.org/
//    File:  HashMap.h
//    Description: This is a class which implements various functions
//          demonstrating the use of a Hash Map.
// ============================================================================
#ifndef TEMPLATE_HASH_MAP
#define TEMPLATE_HASH_MAP
#include <iostream>
#include <string>
#include <sstream>
#include <cstdlib>
 
// if user doesnt define, this is the
// default hash map size
const int HASH_SIZE = 350;
 
template <class Key, class Value>
class HashMap
{
public:
    HashMap(int hashSze = HASH_SIZE);
        /*   Function: Constructor initializes hash map
            Precondition: None
            Postcondition: Defines private variables */
    bool IsEmpty(int keyIndex);
        /*   Function: Determines whether hash map is empty at the given hash
                            map key index
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is empty and the
                             function = false if hash map is not empty */
    bool  IsFull();
        /*   Function: Determines whether hash map is full
            Precondition: Hash map has been created
            Postcondition: The function = true if the hash map is full and the
                             function = false if hash map is not full */
    int Hash(Key m_key);
        /*   Function: Computes and returns a hash map key index for a given item
                        The returned key index is the given cell where the item resides
            Precondition:  Hash map has been created and is not full
            Postcondition: The hash key is returned */
    void Insert(Key m_key, Value m_value);
        /*   Function: Adds new item to the back of the list at a given key in the hash map
                         A unique hash key is automatically generated for each new item
            Precondition:  Hash map has been created and is not full
            Postcondition: Item is in the hash map */
    bool Remove(Key m_key, Value deleteItem);
        /*   Function: Removes the first instance from the map whose value is "deleteItem"
            Precondition:  Hash map has been created and is not empty
            Postcondition: The function = true if deleteItem is found and the
                             function = false if deleteItem is not found */
    void Sort(int keyIndex);
        /*   Function: Sort the items in the map at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The hash map is sorted */
    int TableSize();
        /*   Function: Return the size of the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int TotalElems();
        /*   Function: Return the total number of elements contained in the hash map
            Precondition: Hash map has been initialized
            Postcondition: The size of the hash map is returned */
    int BucketSize(int keyIndex);
        /*   Function: Return the number of items contained in the hash map
                        cell at the given hashmap key index
            Precondition: Hash map has been initialized
            Postcondition: The size of the given key cell is returned */
    int Count(Key m_key, Value searchItem);
        /*   Function: Return the number of times searchItem appears in the map
                        at the given key
            Precondition: Hash map has been initialized
            Postcondition: The number of times searchItem appears in the map is returned */
    int ContainsKey(Key m_key);
        /*   Function: Return the number of times the given key appears in the hashmap
            Precondition: Hash map has been initialized
            Postcondition: The number of times the given key appears in the map is returned */
    void MakeEmpty();
        /*   Function: Initializes hash map to an empty state
            Precondition: Hash map has been created
            Postcondition: Hash map no longer exists */
    ~HashMap();
        /*   Function: Removes the hash map
            Precondition: Hash map has been declared
            Postcondition: Hash map no longer exists */
 
    //  -- ITERATOR CLASS --
    class Iterator;
        /*   Function: Class declaration to the iterator
            Precondition: Hash map has been declared
            Postcondition: Hash Iterator has been declared */
 
    Iterator begin(int keyIndex){return(!IsEmpty(keyIndex)) ? head[keyIndex]:NULL;}
        /*   Function: Returns the beginning of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */
 
    Iterator end(int keyIndex=0){return NULL;}
        /*   Function: Returns the end of the current hashmap key index
            Precondition: Hash map has been declared
            Postcondition: Hash cell has been returned to the Iterator */
 
private:
    struct KeyValue  // struct to hold key/value pairs
    {
        Key key;
        Value value;
    };
    struct node
    {
        KeyValue currentItem;
        node* next;
    };
    node** head; // array of linked list declaration - front of each hash map cell
    int hashSize; // the size of the hash map (how many cells it has)
    int totElems; // holds the total number of elements in the entire table
    int* bucketSize; // holds the total number of elems in each specific hash map cell
};
 
//=========================  Implementation  ================================//
 
template <class Key, class Value>
HashMap<Key, Value>::HashMap(int hashSze)
{
    hashSize = hashSze;
    head = new node*[hashSize];
    bucketSize = new int[hashSize];
    for(int x=0; x < hashSize; ++x)
    {
        head[x] = NULL;
        bucketSize[x] = 0;
    }
    totElems = 0;
}/* End of HashMap */
 
template <class Key, class Value>
bool HashMap<Key, Value>::IsEmpty(int keyIndex)
{
    if(keyIndex >=0 && keyIndex < hashSize)
    {
        return head[keyIndex] == NULL;
    }
    return true;
}/* End of IsEmpty */
 
template <class Key, class Value>
bool HashMap<Key, Value>::IsFull()
{
    try
    {
        node* location = new node;
        delete location;
        return false;
    }
    catch(std::bad_alloc&)
    {
        return true;
    }
}/* End of IsFull */
 
template <class Key, class Value>
int HashMap<Key, Value>::Hash(Key m_key)
{
    long h = 19937;
    std::stringstream convert;
 
    // convert the parameter to a string using "stringstream" which is done
    // so we can hash multiple datatypes using only one function
    convert << m_key;
    std::string temp = convert.str();
 
    for(unsigned x=0; x < temp.length(); ++x)
    {
        h = (h << 6) ^ (h >> 26) ^ temp[x];