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Circular doubly linked list from a text file

itfreakas (30)
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.
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#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;
}
Last edited on
icy1 (596)
1. Determine the data you need in the file to populate your data structures. In this case, just space-separated integers.
2. Iterate over each piece of data in file and insert into your data structures. The <fstream> header makes things easy.

Vectors shouldn't be needed for this. Also, "start", "last", and "counter" should all likely be private members of your class.

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string file_name("my_file_name.txt");
ifstream ifs(file_name);
if (!ifs)
{
    cout << "Error: unable to open '" << file_name << "'\n";
    return -1;
}

int data;
while (ifs >> data)
{
    // Create your node, populate "info", etc.
}
ifs.close();  // Optional.  Closes file immediately, but it would also auto-close when out of scope
itfreakas (30)
Thanks, but when I do this, it always prints: error, unable to open the file :(

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#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()
{
    double_clist cdl;

    ifstream fin("1.txt");
    if (!fin)
    {
        cout << "Error: unable to open " << "1.txt" << endl;
        return -1;
    }
    int info;
    while (fin >> info)
    {
        cdl.create_node(info);
    }
    fin.close();

    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();
            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;
}

icy1 (596)
So by default it's looking in the run-time directory, usually the place where your executable is.
Either put a file named "1.txt" there, or in the code "give/it/the/full/path/to/1.txt".

On some IDEs you can also tweak the starting aka run-time aka working directory.
itfreakas (30)
It still does not work.
icy1 (596)
itfreakas wrote:
It still does not work.

That's probably the vaguest thing in the world you could say.

Say instead, "I went to directory X, where I confirmed my.exe was there. Then I created a file 1.txt with a bunch of integers and placed it in that directory. Then I opened a console in that directory and ran my.exe".

Mention what you tried and how exactly you ran the compiled app.
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