Can't delete node from node list

January 31, 2023

I have a little problem which occurs after trying to execute function delete_all(). Any idea why Visual Studio is throwing me an error:

Invalid address specified to RtlValidateHeap, instruction __debugbreak() or something similar

Everything works perfect until I want to execute this function.

#include <iostream>

using namespace std;

struct node {
    string name = "n1";
    node* prev = NULL;
    node* next = NULL;
};

node* add(node* first, string name) {
    if (first == NULL) {
        return NULL;
    }

    node* nowy = new node;

    if (first->next == NULL) {
        nowy->prev = first;
        first->next = nowy;
    }
    else {
        while (first->next != NULL) {
            first = first->next;
        }
        nowy->prev = first;
        first->next = nowy;
    }

    nowy->name = name;

    return nowy;
}

void writeout(node* first) {
    if (first == NULL) cout << "first = NULL";

    while (first->next != NULL) {
        cout << first->name;
        cout << "\n";
        first = first->next;
    }

    if (first->next == NULL) {
        cout << first->name;
        cout << "\n";
    }
}

void delete_all(node* first) {
    node* temp;
    while (first != NULL) {
        temp = first->next;
        delete first;
        first = temp;
    }
}

int main()
{   
    node n1;

    add(&n1, "n2");
    add(&n1, "n3");

    writeout(&n1);

    delete_all(&n1);
}

>Solution :

You declared an object in main() with automatic storage duration as the first node of the list:

node n1;

You may not destroy it using the delete operator.

Using your approach of the list implementation, you could define the function delete_all() the following way:

void delete_all(node* first) 
{
    if ( first != nullptr )
    {
        while ( first->next != nullptr ) 
        {
            node *temp = first->next;
            first->next = temp->next;
            delete temp;
        }
    }
}

But, it will be much better if initially in main(), you declared a pointer to a node. In this case, you will need to update the functions.