How to delete all nodes in circular doubly linked list?

I've got a problem, because I don't know how to delete all nodes in that kind of list.
What do you think about my solution? Debugger shows me a problem "(...) x was 0xDDDDDDDD"

void del(List *&head) {

    List* ptr = head;

    List* help;

    do {

        List *x = ptr;

        List *y = ptr;

        x = y;

        help = x;

        x = x->next;

        delete y;

        head = NULL;

        ptr = ptr->next;



    } while (help!=NULL);

edited Nov 12 '18 at 13:23

asked Nov 12 '18 at 13:13

user76234

183

1

Only delete what you new. How is your List allocated? Please provide Minimal, Complete, and Verifiable example.
– Algirdas Preidžius
Nov 12 '18 at 13:16

1

Please give your variables names that make sense. See: stackoverflow.com/a/853187/3212865
– spectras
Nov 12 '18 at 13:20

1

You have a node pointer called "help"? What does that signify?
– Lightness Races in Orbit
Nov 12 '18 at 13:24

There does not seem to be a need for so many variables. Could you please clarify what is your intended purpose for each?
– GoodDeeds
Nov 12 '18 at 13:29

2

Removing the unnecessary variable juggling, your loop is equivalent to do { help = ptr; delete ptr; ptr = ptr->next; } while (help != NULL);. Can you spot the bad dereference?
– molbdnilo
Nov 12 '18 at 13:34

|
show 3 more comments

I've got a problem, because I don't know how to delete all nodes in that kind of list.
What do you think about my solution? Debugger shows me a problem "(...) x was 0xDDDDDDDD"

void del(List *&head) {

    List* ptr = head;

    List* help;

    do {

        List *x = ptr;

        List *y = ptr;

        x = y;

        help = x;

        x = x->next;

        delete y;

        head = NULL;

        ptr = ptr->next;



    } while (help!=NULL);

edited Nov 12 '18 at 13:23

asked Nov 12 '18 at 13:13

user76234

183

1

Only delete what you new. How is your List allocated? Please provide Minimal, Complete, and Verifiable example.
– Algirdas Preidžius
Nov 12 '18 at 13:16

1

Please give your variables names that make sense. See: stackoverflow.com/a/853187/3212865
– spectras
Nov 12 '18 at 13:20

1

You have a node pointer called "help"? What does that signify?
– Lightness Races in Orbit
Nov 12 '18 at 13:24

There does not seem to be a need for so many variables. Could you please clarify what is your intended purpose for each?
– GoodDeeds
Nov 12 '18 at 13:29

2

Removing the unnecessary variable juggling, your loop is equivalent to do { help = ptr; delete ptr; ptr = ptr->next; } while (help != NULL);. Can you spot the bad dereference?
– molbdnilo
Nov 12 '18 at 13:34

|
show 3 more comments

I've got a problem, because I don't know how to delete all nodes in that kind of list.
What do you think about my solution? Debugger shows me a problem "(...) x was 0xDDDDDDDD"

void del(List *&head) {

    List* ptr = head;

    List* help;

    do {

        List *x = ptr;

        List *y = ptr;

        x = y;

        help = x;

        x = x->next;

        delete y;

        head = NULL;

        ptr = ptr->next;



    } while (help!=NULL);

edited Nov 12 '18 at 13:23

asked Nov 12 '18 at 13:13

user76234

183

I've got a problem, because I don't know how to delete all nodes in that kind of list.
What do you think about my solution? Debugger shows me a problem "(...) x was 0xDDDDDDDD"

void del(List *&head) {

    List* ptr = head;

    List* help;

    do {

        List *x = ptr;

        List *y = ptr;

        x = y;

        help = x;

        x = x->next;

        delete y;

        head = NULL;

        ptr = ptr->next;



    } while (help!=NULL);

c++

edited Nov 12 '18 at 13:23

asked Nov 12 '18 at 13:13

user76234

183

edited Nov 12 '18 at 13:23

asked Nov 12 '18 at 13:13

user76234

183

edited Nov 12 '18 at 13:23

asked Nov 12 '18 at 13:13

user76234

183

asked Nov 12 '18 at 13:13

user76234

183

asked Nov 12 '18 at 13:13

user76234

183

1

Only delete what you new. How is your List allocated? Please provide Minimal, Complete, and Verifiable example.
– Algirdas Preidžius
Nov 12 '18 at 13:16

1

Please give your variables names that make sense. See: stackoverflow.com/a/853187/3212865
– spectras
Nov 12 '18 at 13:20

1

You have a node pointer called "help"? What does that signify?
– Lightness Races in Orbit
Nov 12 '18 at 13:24

There does not seem to be a need for so many variables. Could you please clarify what is your intended purpose for each?
– GoodDeeds
Nov 12 '18 at 13:29

2

Removing the unnecessary variable juggling, your loop is equivalent to do { help = ptr; delete ptr; ptr = ptr->next; } while (help != NULL);. Can you spot the bad dereference?
– molbdnilo
Nov 12 '18 at 13:34

|
show 3 more comments

1

Only delete what you new. How is your List allocated? Please provide Minimal, Complete, and Verifiable example.
– Algirdas Preidžius
Nov 12 '18 at 13:16

1

Please give your variables names that make sense. See: stackoverflow.com/a/853187/3212865
– spectras
Nov 12 '18 at 13:20

1

You have a node pointer called "help"? What does that signify?
– Lightness Races in Orbit
Nov 12 '18 at 13:24

There does not seem to be a need for so many variables. Could you please clarify what is your intended purpose for each?
– GoodDeeds
Nov 12 '18 at 13:29

2

Removing the unnecessary variable juggling, your loop is equivalent to do { help = ptr; delete ptr; ptr = ptr->next; } while (help != NULL);. Can you spot the bad dereference?
– molbdnilo
Nov 12 '18 at 13:34

Only delete what you new. How is your List allocated? Please provide Minimal, Complete, and Verifiable example.
– Algirdas Preidžius
Nov 12 '18 at 13:16

Please give your variables names that make sense. See: stackoverflow.com/a/853187/3212865
– spectras
Nov 12 '18 at 13:20

You have a node pointer called "help"? What does that signify?
– Lightness Races in Orbit
Nov 12 '18 at 13:24

There does not seem to be a need for so many variables. Could you please clarify what is your intended purpose for each?
– GoodDeeds
Nov 12 '18 at 13:29

Removing the unnecessary variable juggling, your loop is equivalent to do { help = ptr; delete ptr; ptr = ptr->next; } while (help != NULL);. Can you spot the bad dereference?
– molbdnilo
Nov 12 '18 at 13:34

|
show 3 more comments

2 Answers
2

active

oldest

votes

Here is the complete example with the test

struct Node

{

    Node(Node* prev, int val)

        : prev(prev), next(NULL), value(val)

    { }

    Node *prev, *next;

    int value;

};



void clear_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head->next;

        while (curr != NULL && curr != head)

        {

            std::cout << "Deleting " << curr->value << std::endl;

            Node* temp = curr;

            curr = curr->next;

            delete temp;

        };

        delete head;

        head = NULL;

    }

}



void print_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head;

        do

        {

            std::cout << (curr == head ? "Head: " : "") << curr->value << std::endl;

            curr = curr->next;

        } while (curr != NULL && curr != head);

    }

}



int main()

{

    Node* head = new Node(NULL, 0);

    Node* curr = head;

    for (int i = 1; i <= 10; i++)

    {

        Node* prev = curr;

        curr = new Node(prev, i);

        prev->next = curr;

    }

    // Link end to head

    curr->next = head;

    //

    print_list(head);

    clear_list(head);    

    print_list(head);

}

answered Nov 12 '18 at 14:08

serge

59537

thank you so much!
– user76234
Nov 12 '18 at 14:32

@user76234 you are welcome, don't hesitate to mark the answer as solution if it helps.
– serge
Nov 12 '18 at 15:54

add a comment |

List *y = ptr;

delete y;

ptr = ptr->next;

The memory allocated at ptr is gone after delete y. You can not call ptr->next as ptr is dangling at this point and de-referencing it is undefined behavior. Try reordering the last two lines i.e.

ptr = ptr->next;

delete y;

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

Ok, now I understand, thank you.
– user76234
Nov 12 '18 at 14:33

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

Here is the complete example with the test

struct Node

{

    Node(Node* prev, int val)

        : prev(prev), next(NULL), value(val)

    { }

    Node *prev, *next;

    int value;

};



void clear_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head->next;

        while (curr != NULL && curr != head)

        {

            std::cout << "Deleting " << curr->value << std::endl;

            Node* temp = curr;

            curr = curr->next;

            delete temp;

        };

        delete head;

        head = NULL;

    }

}



void print_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head;

        do

        {

            std::cout << (curr == head ? "Head: " : "") << curr->value << std::endl;

            curr = curr->next;

        } while (curr != NULL && curr != head);

    }

}



int main()

{

    Node* head = new Node(NULL, 0);

    Node* curr = head;

    for (int i = 1; i <= 10; i++)

    {

        Node* prev = curr;

        curr = new Node(prev, i);

        prev->next = curr;

    }

    // Link end to head

    curr->next = head;

    //

    print_list(head);

    clear_list(head);    

    print_list(head);

}

answered Nov 12 '18 at 14:08

serge

59537

thank you so much!
– user76234
Nov 12 '18 at 14:32

@user76234 you are welcome, don't hesitate to mark the answer as solution if it helps.
– serge
Nov 12 '18 at 15:54

add a comment |

Here is the complete example with the test

struct Node

{

    Node(Node* prev, int val)

        : prev(prev), next(NULL), value(val)

    { }

    Node *prev, *next;

    int value;

};



void clear_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head->next;

        while (curr != NULL && curr != head)

        {

            std::cout << "Deleting " << curr->value << std::endl;

            Node* temp = curr;

            curr = curr->next;

            delete temp;

        };

        delete head;

        head = NULL;

    }

}



void print_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head;

        do

        {

            std::cout << (curr == head ? "Head: " : "") << curr->value << std::endl;

            curr = curr->next;

        } while (curr != NULL && curr != head);

    }

}



int main()

{

    Node* head = new Node(NULL, 0);

    Node* curr = head;

    for (int i = 1; i <= 10; i++)

    {

        Node* prev = curr;

        curr = new Node(prev, i);

        prev->next = curr;

    }

    // Link end to head

    curr->next = head;

    //

    print_list(head);

    clear_list(head);    

    print_list(head);

}

answered Nov 12 '18 at 14:08

serge

59537

thank you so much!
– user76234
Nov 12 '18 at 14:32

@user76234 you are welcome, don't hesitate to mark the answer as solution if it helps.
– serge
Nov 12 '18 at 15:54

add a comment |

Here is the complete example with the test

struct Node

{

    Node(Node* prev, int val)

        : prev(prev), next(NULL), value(val)

    { }

    Node *prev, *next;

    int value;

};



void clear_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head->next;

        while (curr != NULL && curr != head)

        {

            std::cout << "Deleting " << curr->value << std::endl;

            Node* temp = curr;

            curr = curr->next;

            delete temp;

        };

        delete head;

        head = NULL;

    }

}



void print_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head;

        do

        {

            std::cout << (curr == head ? "Head: " : "") << curr->value << std::endl;

            curr = curr->next;

        } while (curr != NULL && curr != head);

    }

}



int main()

{

    Node* head = new Node(NULL, 0);

    Node* curr = head;

    for (int i = 1; i <= 10; i++)

    {

        Node* prev = curr;

        curr = new Node(prev, i);

        prev->next = curr;

    }

    // Link end to head

    curr->next = head;

    //

    print_list(head);

    clear_list(head);    

    print_list(head);

}

answered Nov 12 '18 at 14:08

serge

59537

Here is the complete example with the test

struct Node

{

    Node(Node* prev, int val)

        : prev(prev), next(NULL), value(val)

    { }

    Node *prev, *next;

    int value;

};



void clear_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head->next;

        while (curr != NULL && curr != head)

        {

            std::cout << "Deleting " << curr->value << std::endl;

            Node* temp = curr;

            curr = curr->next;

            delete temp;

        };

        delete head;

        head = NULL;

    }

}



void print_list(Node*& head)

{

    if (head != NULL)

    {

        Node* curr = head;

        do

        {

            std::cout << (curr == head ? "Head: " : "") << curr->value << std::endl;

            curr = curr->next;

        } while (curr != NULL && curr != head);

    }

}



int main()

{

    Node* head = new Node(NULL, 0);

    Node* curr = head;

    for (int i = 1; i <= 10; i++)

    {

        Node* prev = curr;

        curr = new Node(prev, i);

        prev->next = curr;

    }

    // Link end to head

    curr->next = head;

    //

    print_list(head);

    clear_list(head);    

    print_list(head);

}

answered Nov 12 '18 at 14:08

serge

59537

answered Nov 12 '18 at 14:08

serge

59537

answered Nov 12 '18 at 14:08

serge

59537

answered Nov 12 '18 at 14:08

serge

59537

thank you so much!
– user76234
Nov 12 '18 at 14:32

@user76234 you are welcome, don't hesitate to mark the answer as solution if it helps.
– serge
Nov 12 '18 at 15:54

add a comment |

thank you so much!
– user76234
Nov 12 '18 at 14:32

@user76234 you are welcome, don't hesitate to mark the answer as solution if it helps.
– serge
Nov 12 '18 at 15:54

thank you so much!
– user76234
Nov 12 '18 at 14:32

@user76234 you are welcome, don't hesitate to mark the answer as solution if it helps.
– serge
Nov 12 '18 at 15:54

add a comment |

List *y = ptr;

delete y;

ptr = ptr->next;

The memory allocated at ptr is gone after delete y. You can not call ptr->next as ptr is dangling at this point and de-referencing it is undefined behavior. Try reordering the last two lines i.e.

ptr = ptr->next;

delete y;

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

Ok, now I understand, thank you.
– user76234
Nov 12 '18 at 14:33

add a comment |

List *y = ptr;

delete y;

ptr = ptr->next;

The memory allocated at ptr is gone after delete y. You can not call ptr->next as ptr is dangling at this point and de-referencing it is undefined behavior. Try reordering the last two lines i.e.

ptr = ptr->next;

delete y;

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

Ok, now I understand, thank you.
– user76234
Nov 12 '18 at 14:33

add a comment |

List *y = ptr;

delete y;

ptr = ptr->next;

The memory allocated at ptr is gone after delete y. You can not call ptr->next as ptr is dangling at this point and de-referencing it is undefined behavior. Try reordering the last two lines i.e.

ptr = ptr->next;

delete y;

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

List *y = ptr;

delete y;

ptr = ptr->next;

The memory allocated at ptr is gone after delete y. You can not call ptr->next as ptr is dangling at this point and de-referencing it is undefined behavior. Try reordering the last two lines i.e.

ptr = ptr->next;

delete y;

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

answered Nov 12 '18 at 13:53

Manoj R

2,67211329

Ok, now I understand, thank you.
– user76234
Nov 12 '18 at 14:33

add a comment |

Ok, now I understand, thank you.
– user76234
Nov 12 '18 at 14:33

Ok, now I understand, thank you.
– user76234
Nov 12 '18 at 14:33

add a comment |

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