c++ linked list insert function

Question

I get a compile error for a create function I use with the insert function. It works though when I do the different calls in the if clause, but I want to move it to a seperate create function instead. Any help regarding the compile error I get is appreciated

|76|error: cannot convert list_link*' tosorted_list::list_link*' in assignment|

The header file

class sorted_list
{
public:
    sorted_list(); // Constructor declaration
    ~sorted_list(); // Destructor declaration

    void insert(int key, double value);
    void print();


private:
    class list_link
    {
        // Declarations
        public:
        my_key_type key;
        my_value_type value;
        list_link *next;
    };
    list_link* first;

};

The functions

void sorted_list::insert(int key, double value)
{
    list_link *curr, *prev;

    curr = first;

    while(curr)
    {
        prev = curr;
        curr = curr->next;
    }
    if(first == 0 || prev == 0) //if empty or add first
    {
        cout << "empty list" << endl;
        list_link *new_link = new list_link;
        new_link->key = key;
        new_link->value = value;
        new_link->next = 0;
        first = new_link;

    }
    else
    {
        cout << "add" << endl;
        prev->next = create(key, value, 0);
    }
}

create function

list_link* create(my_key_type key, my_value_type value, list_link* next)
{
   // creates the node;
   list_link *new_link = new list_link;

   // add values to the node;
   new_link->key = key;
   new_link->value = value;
   new_link->next = next;

  return new_link;
}

Michael Aaron Safyan · Accepted Answer · 2010-11-03 01:09:02Z

1

The class list_link is:

Declared in the scope of sorted_list
Marked as private

In order to have a freestanding function create an object of this type, you will need to make the type public, and you will also need to either prefix it with sorted_list::, or you wil need to declare it outside of the sorted_list class. I should add that you use list_link as a simple data object, where there are no methods and the fields are public, and so -- from a purely stylistic perspective -- I would recommend declaring it as a struct instead of a class, which also removes the need for public.

answered Nov 3, 2010 at 1:09

Michael Aaron Safyan

96k16 gold badges140 silver badges200 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

starcorn Over a year ago

is there's some other way, since I want to keep the Node creation internal to the class only

Michael Aaron Safyan Over a year ago

@starcorn, if it is internal, then don't use a freestanding function; make the create function a private function of sorted_list.

starcorn Over a year ago

ah, that's what I thought but I kept struggeling with it for quite some time before I saw that I had to write sorted_list::list_link sorted_list::create() {} in the .cc file. Anyway I think I sorted it out now. Thanks

Igbanam · Accepted Answer · 2010-11-03 04:15:54Z

I am not an authority in C++ but I think the problem comes with the way you are scpping things.

The list_link class is private. I recommend this being public since a class is only a blueprint through which object instances can be created. What you can keep private is the actual pointer to the linked list, list_link *first.
Since the list_link class is nested under the sorted_list class, you have to go through the sorted_list scope each time you try to access the list_link class.

Try this out for a fix:

class sorted_list
{
public:
    sorted_list(); // Constructor declaration
    ~sorted_list(); // Destructor declaration

    void insert(int key, double value);
    void print();


    class list_link
    {
        // Declarations
        public:
        my_key_type key;
        my_value_type value;
        list_link *next;
    };
private:
    list_link* first;

};

sorted_list::list_link* create(my_key_type key, my_value_type value, sorted_list::list_link* next)
{
   // creates the node;
    sorted_list::list_link *new_link = new sorted_list::list_link;

   // add values to the node;
   new_link->key = key;
   new_link->value = value;
   new_link->next = next;

  return new_link;
}

void sorted_list::insert(int key, double value)
{
    list_link *curr, *prev;

    curr = first;

    while(curr)
    {
        prev = curr;
        curr = curr->next;
    }
    if(first == 0 || prev == 0) //if empty or add first
    {
        cout << "empty list" << endl;
        list_link *new_link = new list_link;
        new_link->key = key;
        new_link->value = value;
        new_link->next = 0;
        first = new_link;

    }
    else
    {
        cout << "add" << endl;
        prev->next = create(key, value, 0);
    }
}

Hope this helps. Cheers.

Collectives™ on Stack Overflow

c++ linked list insert function

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related