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;
}

[keskiverto]

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

Vector? Why?

Reading from file should be relatively trivial:

while ( read entry from file ) {
  add entry to container
}

It seems that one "entry" is one int. Furthermore, you probably want to preserve the order of entries.

void fetch( std::ifsream& in, T & container ) {
  int entry {};
  while ( in >> entry ) {
    container.push_back( entry );
  }
}

If T were std::vector<int>, the read-part would be done, but then you have to copy from vector to list:

std::vector<int> dummy;
fetch( infile, dummy );
for ( auto e : dummy ) list.push_back( e );

That, however, seems waste of memory and instructions.
Lets make T a double_clist:

double_clist cdl;
fetch( infile, cdl );
// done 

Now we have added a requirement that the double_clist should have member push_back(int foo) that creates a new node with value foo and inserts it at the "logical end" of the list.
You don't quite have such member.


Note: one does never ever use free() on memory that came from new. Use delete.

Note: your last is redundant. It is always, by definition of circular, the same as start->prev.

Note: you use syntax struct node *s;. The struct is not necessary in C++. Use plain node *s;

Note: you define three global variables: start, last, and counter. You can now have only one list. Change those globals into class members.