How to call a recursive linked list traversal function in C++

Question

I have this function:

    void TraverseRecursive ( Node * head, void (*visit) (Node *) )
    {
      if ( head != nullptr )
      {
        visit( head ) ;
        TraverseRecursive( head->next, visit ) ;
      }
    }

And I'm trying to call it in main.cpp with

TraverseRecursive ( head, TraverseRecursive ) ;

Which gives me the error "argument of type "void (*)(Node *head, void (*visit)(Node ))" is incompatible with parameter of type "void ()(Node *)" "

So how do I correctly call it? I am just learning linked lists and obviously don't understand what

 void (*visit) (Node *)

means at all.

If you're just learning about recursion then by all means recurse away, but as @ikegami points out, traversing a list is an inherently non-recursive activity. You pay a run-time price for using recursion, so avoid it when possible unless it truly simplifies your code. — Matt Coubrough
– Matt Coubrough, Commented May 31, 2014 at 23:26

ikegami · Accepted Answer · 2014-05-31 23:40:02Z

1

The second argument should be a function to call back for every node in the list. It only takes a single parameter (the node to "visit").

void visitor(Node *node)
{
  printf("%s\n", node->data);  // Or whatever
}

TraverseRecursive( head, visitor ) ;

Side note: What wasteful use of recursion. If you're lucky, the compiler will optimize it away. You should be using

void TraverseRecursive( Node * head, void (*visit) (Node *) )
{
  for (; head != nullptr; head = head->next)
  {
    visit( head ) ;
  }
}

edited May 31, 2014 at 23:40

answered May 31, 2014 at 23:22

ikegami

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1 Comment

MrPickles7 Over a year ago

Thanks people! I got excited to use recursion because I was going to call a display function, then just switch the visit... and Traverse... lines to make it display backwards. I was trying to combine them into one horrible abomination, but thanks to ya'll now I can call Display from my traverse!

wonce · Accepted Answer · 2014-05-31 23:23:06Z

0

void (*visit) (Node *)

means "pointer to a function taking one argument of type Node* and returning void". But TraverseRecurive takes two argumenst and is therefore of different type. You need to define a function like

void doSomething(Node* n)
{
}

and pass it to TraverseRecursive

answered May 31, 2014 at 23:23

wonce

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