C ++创建链接列表的链接列表

Question

So, this is a part of my "linked_list.h" header:

template <typename T>
class Linked_list {
public:
  Linked_list();
  ~Linked_list();

  void add_first(const T& x);
  //...
};

And a part of my implementation:

template <typename T>
line 22: void Linked_list<T> :: add_first(const T& x)
{
  Node<T>* aux;
  aux = new Node<T>;
  aux->info = x;
  aux->prev = nil;
  aux->next = nil->next;
  nil->next->prev = aux;
  nil->next = aux;
}

and I'm trying to make a linked list of linked lists of strings and add strings in one linked list of my linked list, like this:

Linked_list<Linked_list<string> > *l;
l[0]->add_first("list");
//also I've tried l[0].add_first("list"); but it didn't work either

Thank you.

Later edit: When I try l[0]->add_first("list") these are the errors:

main.cc: In function ‘int main()’:
main.cc:22:22: error: no matching function for call      to‘Linked_list<Linked_list<std::basic_string<char> > >::add_first(const char [4])’
main.cc:22:22: note: candidate is:
In file included from main.cc:6:0:
linked_list.cc:28:6: note: void Linked_list<T>::add_first(const T&) [with T = Linked_list<std::basic_string<char> >]
linked_list.cc:28:6: note:   no known conversion for argument 1 from ‘const char [4]’ to ‘const Linked_list<std::basic_string<char> >&’

Later later edit: It worked finally, thank you for the ideas: I did just this and it's okay now:

Linked_list<Linked_list<string> > l;
l[0].add_first("list");

And it works :D. Thanks again !

Neah..actually it doesn't work..

Answer 1

You have created a pointer to linked list and have never pointed it to existent element. Either use new to allocate dynamic memory or use an object instead of a pointer.

Like so:

Linked_list<Linked_list<string> > *l = new Linked_list<Linked_list<string> >();

Or like so:

Linked_list<Linked_list<string> > l;

The fact that you are using the operator[] may mean you meant to use an array so probably you will have to go with first version.

Answer 2

you're trying to access uninitialized pointer. use

Linked_list<Linked_list<string> > lol;
Linked_list<string> los;
los.add_first("list");
lol.add_first(los);

or

Linked_list<Linked_list<string> > *p = new Linked_list<Linked_list<string> >;