Circular doubly linked list from a text file

[itfreakas]

Hello everyone, I am having a hard time figuring out how to form a circular doubly linked list from a text file. I know I have to store the data from the text file to a vector and then somehow store each vector element to the circular doubly linked list using the loop, but I am just not really sure how to do it and I cannot find any suitable example in the internet. Please help...
Here is the code I use, before doing any of these operations I want to form a circular doubly linked list with the data from the text file.

#include <iostream>
#include <fstream>
#include <vector>
#include <cstdio>
#include <cstdlib>
using namespace std;

struct node
{
int info;
struct node *next;
struct node *prev;
}*start, *last;
int counter = 0;

class double_clist
{
public:
node *create_node(int);
void insert_begin();
void insert_last();
void insert_pos();
void delete_pos();
void display();
double_clist()
{
start = NULL;
last = NULL;
}
};

int main()
{
int choice;
double_clist cdl;
while (1)
{
cout<<"Operations on Doubly Circular linked list"<<endl;
cout<<"1.Insert at Beginning"<<endl;
cout<<"2.Insert at Last"<<endl;
cout<<"3.Insert at Position"<<endl;
cout<<"4.Delete at Position"<<endl;
cout<<"5.Display List"<<endl;
cout<<"6.Exit"<<endl;
cout<<"Enter your choice : ";
cin>>choice;
switch(choice)
{
case 1:
cdl.insert_begin();
break;
case 2:
cdl.insert_last();
break;
case 3:
cdl.insert_pos();
break;
case 4:
cdl.delete_pos();
break;
case 5:
cdl.display();
break;
case 6:
exit(1);
default:
cout<<"Wrong choice"<<endl;
}
}
return 0;
}

node* double_clist::create_node(int value)
{
counter++;
struct node *temp;
temp = new(struct node);
temp->info = value;
temp->next = NULL;
temp->prev = NULL;
return temp;
}

void double_clist::insert_begin()
{
int value;
cout<<endl<<"Enter the element to be inserted: ";
cin>>value;
struct node *temp;
temp = create_node(value);
if (start == last && start == NULL)
{
cout<<"Element inserted in empty list"<<endl;
start = last = temp;
start->next = last->next = NULL;
start->prev = last->prev = NULL;
}
else
{
temp->next = start;
start->prev = temp;
start = temp;
start->prev = last;
last->next = start;
cout<<"Element inserted"<<endl;
}
}

void double_clist::insert_last()
{
int value;
cout<<endl<<"Enter the element to be inserted: ";
cin>>value;
struct node *temp;
temp = create_node(value);
if (start == last && start == NULL)
{
cout<<"Element inserted in empty list"<<endl;
start = last = temp;
start->next = last->next = NULL;
start->prev = last->prev = NULL;
}
else
{
last->next = temp;
temp->prev = last;
last = temp;
start->prev = last;
last->next = start;
}
}

void double_clist::insert_pos()
{
int value, pos, i;
cout<<endl<<"Enter the element to be inserted: ";
cin>>value;
cout<<endl<<"Enter the postion of element inserted: ";
cin>>pos;
struct node *temp, *s, *ptr;
temp = create_node(value);
if (start == last && start == NULL)
{
if (pos == 1)
{
start = last = temp;
start->next = last->next = NULL;
start->prev = last->prev = NULL;
}
else
{
cout<<"Position out of range"<<endl;
counter--;
return;
}
}
else
{
if (counter < pos)
{
cout<<"Position out of range"<<endl;
counter--;
return;
}
s = start;
for (i = 1;i <= counter;i++)
{
ptr = s;
s = s->next;
if (i == pos - 1)
{
ptr->next = temp;
temp->prev = ptr;
temp->next = s;
s->prev = temp;
cout<<"Element inserted"<<endl;
break;
}
}
}
}

void double_clist::delete_pos()
{
int pos, i;
node *ptr, *s;
if (start == last && start == NULL)
{
cout<<"List is empty, nothing to delete"<<endl;
return;
}
cout<<endl<<"Enter the postion of element to be deleted: ";
cin>>pos;
if (counter < pos)
{
cout<<"Position out of range"<<endl;
return;
}
s = start;
if(pos == 1)
{
counter--;
last->next = s->next;
s->next->prev = last;
start = s->next;
free(s);
cout<<"Element Deleted"<<endl;
return;
}
for (i = 0;i < pos - 1;i++ )
{
s = s->next;
ptr = s->prev;
}
ptr->next = s->next;
s->next->prev = ptr;
if (pos == counter)
{
last = ptr;
}
counter--;
free(s);
cout<<"Element Deleted"<<endl;
}

void double_clist::display()
{
int i;
struct node *s;
if (start == last && start == NULL)
{
cout<<"The List is empty, nothing to display"<<endl;
return;
}
s = start;
for (i = 0;i < counter-1;i++)
{
cout<<s->info<<"<->";
s = s->next;
}
cout<<s->info<<endl;
}

[dhayden]

When posting code, please use code tags. Edit your post, highlight the code and then click the "<>" button to the right of the edit window. This will cause the code to appear with line numbers and syntax highlighting. It makes it much easier for us to refer to specific parts of the post.

start, last and counter should members of class double_clist. Otherwise you can't really have a program with two separate lists.

create_node() should probably be private. Some one using the list shouldn't have to worry about creating nodes.

insert_begin() should just insert a value at the beginning of the list. E.g., it should be void insert_begin(int value). All the code that prompts for the value should be part of the main program, not part of the list class. After all, when it comes to inserting the values from a file, you won't want to prompt the user for a value.

Same comment applies to the other methods.

insert_begin(): you need to set last when inserting into an empty list.
insert_last(): you need to set start when inserting into an empty list.
insert_pos(). Exactly where does it insert the item? Before pos? After pos? Is the first item considered position 0 or position 1? Either way, when inserting into non-empty list, you may need to update start and/or last.

[itfreakas]

Yeah, well thanks, but I am asking how to store the data inside this list from a vector?

[doug4]

Why do you need to store the data into a vector?

When you read each value, instead of putting it into the vector, put it into the list.

Change your insert...() functions to take an argument. Instead of asking the user for a value, pass the value read from the file into the function.

int value;
infile >> value;
insert_begin(value);

[itfreakas]

Thanks, but now another problem, after reading the text file and choosing to display the list elements, it always prints 0. Why is that? :(

#include <iostream>
#include <fstream>
#include <vector>
#include <cstdio>
#include <cstdlib>
using namespace std;

struct node
{
    int info;
    struct node *next;
    struct node *prev;
}*start, *last;
int counter = 0;

class double_clist
{
    public:
        node *create_node(int);
        void insert_begin(int value);
        void insert_last();
        void insert_pos();
        void delete_pos();
        void display();
        double_clist()
        {
            start = NULL;
            last = NULL;
        }
};

int main()
{
    double_clist cdl;

    ifstream fin("1.txt");
    int value;
    fin >> value;
    cdl.insert_begin(value);

    int choice;
    while (1)
    {
        cout<<"Operations on Doubly Circular linked list"<<endl;
        cout<<"1.Insert at Beginning"<<endl;
        cout<<"2.Insert at Last"<<endl;
        cout<<"3.Insert at Position"<<endl;
        cout<<"4.Delete at Position"<<endl;
        cout<<"5.Display List"<<endl;
        cout<<"6.Exit"<<endl;
        cout<<"Enter your choice : ";
        cin>>choice;
        switch(choice)
        {
        case 1:
            cdl.insert_begin(value);
            break;
        case 2:
            cdl.insert_last();
            break;
        case 3:
            cdl.insert_pos();
            break;
        case 4:
            cdl.delete_pos();
            break;
        case 5:
            cdl.display();
            break;
        case 6:
            exit(1);
        default:
            cout<<"Wrong choice"<<endl;
        }
    }
    return 0;
}

node* double_clist::create_node(int value)
{
    counter++;
    struct node *temp;
    temp = new(struct node);
    temp->info = value;
    temp->next = NULL;
    temp->prev = NULL;
    return temp;
}

void double_clist::insert_begin(int value)
{
    struct node *temp;
    temp = create_node(value);
    if (start == last && start == NULL)
    {
        cout<<"Element inserted in empty list"<<endl;
        start = last = temp;
        start->next = last->next = NULL;
        start->prev = last->prev = NULL;
    }
    else
    {
        temp->next = start;
        start->prev = temp;
        start = temp;
        start->prev = last;
        last->next = start;
        cout<<"Element inserted"<<endl;
    }
}

void double_clist::insert_last()
{
    int value;
    cout<<endl<<"Enter the element to be inserted: ";
    cin>>value;
    struct node *temp;
    temp = create_node(value);
    if (start == last && start == NULL)
    {
        cout<<"Element inserted in empty list"<<endl;
        start = last = temp;
        start->next = last->next = NULL;
        start->prev = last->prev = NULL;
    }
    else
    {
        last->next = temp;
        temp->prev = last;
        last = temp;
        start->prev = last;
        last->next = start;
    }
}

void double_clist::insert_pos()
{
    int value, pos, i;
    cout<<endl<<"Enter the element to be inserted: ";
    cin>>value;
    cout<<endl<<"Enter the postion of element inserted: ";
    cin>>pos;
    struct node *temp, *s, *ptr;
    temp = create_node(value);
    if (start == last && start == NULL)
    {
        if (pos == 1)
        {
            start = last = temp;
            start->next = last->next = NULL;
            start->prev = last->prev = NULL;
        }
        else
        {
            cout<<"Position out of range"<<endl;
            counter--;
            return;
        }
    }
    else
    {
        if (counter < pos)
        {
             cout<<"Position out of range"<<endl;
             counter--;
             return;
        }
        s = start;
        for (i = 1;i <= counter;i++)
        {
            ptr = s;
            s = s->next;
            if (i == pos - 1)
            {
                ptr->next = temp;
                temp->prev = ptr;
                temp->next = s;
                s->prev = temp;
                cout<<"Element inserted"<<endl;
                break;
            }
        }
    }
}

void double_clist::delete_pos()
{
    int pos, i;
    node *ptr, *s;
    if (start == last && start == NULL)
    {
        cout<<"List is empty, nothing to delete"<<endl;
        return;
    }
    cout<<endl<<"Enter the postion of element to be deleted: ";
    cin>>pos;
    if (counter < pos)
    {
        cout<<"Position out of range"<<endl;
        return;
    }
    s = start;
    if(pos == 1)
    {
        counter--;
        last->next = s->next;
        s->next->prev = last;
        start = s->next;
        free(s);
        cout<<"Element Deleted"<<endl;
        return;
    }
    for (i = 0;i < pos - 1;i++ )
    {
        s = s->next;
        ptr = s->prev;
    }
    ptr->next = s->next;
    s->next->prev = ptr;
    if (pos == counter)
    {
        last = ptr;
    }
    counter--;
    free(s);
    cout<<"Element Deleted"<<endl;
}

void double_clist::display()
{
    int i;
    struct node *s;
    if (start == last && start == NULL)
    {
        cout<<"The List is empty, nothing to display"<<endl;
        return;
    }
    s = start;
    for (i = 0;i < counter-1;i++)
    {
        cout<<s->info<<"<->";
        s = s->next;
    }
    cout<<s->info<<endl;
}