Question

I am trying to make a recursion function that will print all the elements in a linked list backward.

This is the function that I have made:

void lista::printBack(node *pocetak) {
    if (pocetak==NULL) {
        return ;
    }    
    printBack(pocetak->sljedeci);
    cout<<pocetak->podatak<<" ";
}

Now for the question. I want to set default value of the parameter pocetak, so that the function can print the list without the start value.

But when I do this:

void lista::printBack(node *pocetak = head) 
{
    if (pocetak==NULL) {
        return ;
    }

    printBack(pocetak->sljedeci);

    cout<<pocetak->podatak<<" ";
}

I always get a error message:
main.cpp:17:19: error: no matching function for call to ‘lista::printBack()’
main.cpp:17:19: note: candidate is:
lista.h:20:10: note: void lista::printBack(node*)
lista.h:20:10: note: candidate expects 1 argument, 0 provided

Is that any way I can do this? Thank you.

Answer 1

You need to specify the default argument in the header file (the implementation lista::printBack(node* pocetak=head) is not enough)

// lista.h
struct node;
node* head;

struct lista
{
  void printBack(node* pocetak=head);
};

Note that this means you will need to have a valid node* head declared before the lista type is defined, the best way for which is t use forward declaration (see above). Also, head will be a global variable, which is usually not a good idea.

EDIT: fixed type names