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fstream help

Apr 25, 2018 at 2:52pm
itfreakas (30)
Hello everyone, I am having a hard time figuring out how to form a circular doubly linked list from a text file. With this code I manage to read the start node and the last node from the text file, but I am not sure how to read all the data to the list properly and in a rational way as possible. What should I add to my code?

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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 , *t, *q;
int counter = 0;

class double_clist
{
    public:
        node *create_node(int);
        void insert_begin(int value);
        void insert_last(int value);
        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);
    cdl.insert_last(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(value);
            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)
{
    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 position 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;
}
Edit & run on cpp.sh
Last edited on Apr 25, 2018 at 2:53pm
Apr 25, 2018 at 3:23pm
coder777 (8447)
This:
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while(fin >> value)
{
    cdl.insert_last(value);
}
Apr 25, 2018 at 4:32pm
itfreakas (30)
I am trying to implement this while loop, but it still always print that the list is empty...

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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 , *t, *q;
int counter = 0;

class double_clist
{
    public:
        node *create_node(int);
        void insert_begin(int value);
        void insert_last(int value);
        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;
    while(fin >> value)
    {
        cdl.insert_last(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(value);
            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)
{
    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 position 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;
}
Edit & run on cpp.sh
Apr 26, 2018 at 10:20pm
Enoizat (1343)
it still always print that the list is empty

Supposing your “1.txt” looks like:
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

this version prints the list (please note: I haven’t carried out other tests, it’s just for hints):
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#include <fstream>
#include <iostream>

struct node {
    int info;
    struct node *next;
    struct node *prev;
    node();
};

node::node() : info {}, next { nullptr }, prev { nullptr }  {}

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

double_clist::double_clist()
    : start { nullptr }, last { nullptr }, counter {}
{}

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

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

void double_clist::insert_last(int value)
{
    node* temp = create_node(value);
    if (start == last && start == nullptr) {
        start = last = temp;
        start->next = last->next = nullptr;
        start->prev = last->prev = nullptr;
        std::cout << "Element inserted in empty list\n";
    } else {
        last->next = temp;
        temp->prev = last;
        last = temp;
        start->prev = last;
        last->next = start;
    }
}

void double_clist::insert_pos()
{
    std::cout << "\nEnter the element to be inserted: ";
    int value;
    std::cin >> value;
    std::cout << "\nEnter the position of element inserted: ";
    int pos;
    std::cin >> pos;
    node *temp = create_node(value);
    if (start == last && start == nullptr) {
        if (pos == 1) {     // call insert_begin() ?
            start = last = temp;
            start->next = last->next = nullptr;
            start->prev = last->prev = nullptr;
        } else {
            std::cout << "Position out of range\n";
            counter--;
            delete temp;    // <---
            return;
        }
    } else {
        if (counter < pos) {
            std::cout << "Position out of range\n";
            counter--;
            delete temp;    // <---
            return;
        }
        node* s = start;
        for (int i = 1; i <= counter; ++i) {
            node* ptr = s;
            s = s->next;
            if (i == pos - 1) {
                ptr->next = temp;
                temp->prev = ptr;
                temp->next = s;
                s->prev = temp;
                std::cout << "Element inserted\n";
                break;
            }
        }
    }
}

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

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

int main()
{
    double_clist cdl;

    std::ifstream fin("1.txt");
    for(int value {}; fin >> value; /**/) { cdl.insert_last(value); }
    int choice;
    while (1)
    {
        std::cout << "Operations on Doubly Circular linked list\n"
                     "1.Insert at Beginning\n"
                     "2.Insert at Last\n"
                     "3.Insert at Position\n"
                     "4.Delete at Position\n"
                     "5.Display List\n"
                     "6.Exit\n"
                     "Enter your choice : ";
        std::cin >> choice;
        int value { 666 };
        switch(choice) {
        case 1: cdl.insert_begin(value); break;
        case 2: cdl.insert_last(value);  break;
        case 3: cdl.insert_pos();        break;
        case 4: cdl.delete_pos();        break;
        case 5: cdl.display();           break;
        case 6: return 1;
        default: std::cout << "Wrong choice\n"; break;
        }
    }
    return 0;
}
Edit & run on cpp.sh


Output:
Element inserted in empty list
Operations on Doubly Circular linked list
1.Insert at Beginning
2.Insert at Last
3.Insert at Position
4.Delete at Position
5.Display List
6.Exit
Enter your choice : 5
1 <-> 2 <-> 3 <-> 4 <-> 5 <-> 6 <-> 7 <-> 8 <-> 9 <-> 10 <-> 
11 <-> 12 <-> 13 <-> 14 <-> 15 <-> 16 <-> 17 <-> 18 <-> 19 <-> 20 <-> 
21 <-> 22 <-> 23 <-> 24 <-> 25 <-> 26 <-> 27 <-> 28 <-> 29 <-> 30 <-> 
31 <-> 32 <-> 33 <-> 34
Operations on Doubly Circular linked list
1.Insert at Beginning
2.Insert at Last
3.Insert at Position
4.Delete at Position
5.Display List
6.Exit
Enter your choice : 6

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