Problem with custom linked list using strings.

[BRod423]

Hi, I have an assignment to create a custom linked list class to store strings, but I'm having some issues.

struct node {
  node(string current) { data=current; next=NULL; }
  string data;
  node *next;
};

class list {
public:
  list(int N=0, string current);
  ~list();
  bool empty() const { return N == 0; }
  void clear();

  void insert(int, const string &);

  void push_front(const string &current);

  friend ostream & operator<<(ostream &out, const list &current);

private:
  int N;
  node *head;
  node *findnode(int);
};

list::list(int M, string current) {
  N = M;
  head = new node;
  for (int i=0; i<N; i++)
    insert(0, current);
}

list::~list() {
  clear();
  delete head;
}


void list::clear() {
  while (!empty()) remove(0);
}

void list::insert(int i, const string &din) {
  node *p = new node(din);
  node *pp = findnode(i-1);
  p->next = pp->next;
  pp->next = p;
  N++;
}

inline
node *list::findnode(int i) {
  if (i == -1)
    return head;
  node *p = head->next;
  while (i--)
    p = p->next;
  return p;
}


void list::push_front(const string &current) {
  head = new node;
  head->next;
}

ostream& operator<<(ostream& out, const list& current)
{
  out << current;
  return out;
}

I'm getting

"terminate called after throwing an instance of 'std::logic_error'
what(): basic_string::_S_construct null not valid"

Which I think is because a string is set to null, I think it would probably be in line 2, but I'm unsure, and unsure how to fix it.

(background: we were given a single linked list program to edit to accept strings for another use).

[Gkneeus]

line 9 list(int N=0, string current);
change to
list(int M, string current);


line 31 and 32

list::list(int M, string current) {
  N = M;

The declaration of your constructor on line 9 does not match with this. You can't have an N variable in the class and and pass in an N variable to the constructor.


Line 33

 head = new node;

you are using the default constructor here, you don't have one defined.
is this what you want?
head = new node("overloaded constructor");