Calling operator<<?

[Kman]

My program is telling me my Book class doesn't have an operator<< function even though it does. I'm trying to call it from my BST program. I did #include the Book.h file in both my BST.h and BST.cpp files.

Here it is in my Book.h file:

  #include <string>
#ifndef Book_Header
#define Book_Header

class Book
{
public:
friend std::ostream& operator<<(std::ostream& os, Book& b);
}

std::ostream& operator<<(std::ostream& os, Book& b);

Here's me calling it in my BST.cpp file. Did I call it incorrectly?

std::ostream &operator<<(std::ostream& os, BST& rhs)
{
	while (rhs.root != NULL)
	{
		Book::operator<<(os, rhs.root->left);
		return os << rhs.root->bookNode;
		Book::operator<<(os, rhs.root->right);
	}
	
};

[keskiverto]

What is the type of rhs.root->left and rhs.root->right ?

[ne555]

Book doesn't have a operator<<.
You have a global function, called operator<< that receives an ostream and a Book, and that has access to the privates of the Book.
Which I think that you are calling correctly in line 6.

The error probably point you to lines 5 and 7, where I suspect you are trying to make a recursive call.

[Kman]

Sorry, here's the typing of the entire struct in BST.h:

class BST
{
private:
	struct Node
	{
		Node *left;
		Node *right;
		Book bookNode;
	};

	Node *root;
	Node *current;

@ne555 Yeah, the errors are on lines 5 and 7 and I'm trying to call it recursively. I just don't know how to call what I need using the operator<< in Book.h.

[keskiverto]

The os and rhs.root->bookNode are std::ostream and Book, respectively, but on the erroneous lines you are calling

std::ostream & Book::operator<<( std::ostream&, Node* )

That obviously fails, for Book has no member operator<< of any kind.

Besides, operators are usually called with the other syntax:
os << rhs.root->left << rhs.root->bookNode << rhs.root->right;


Make a standard standalone recursive function that takes ( std::ostream&, Node* ) and then call it from the operator<<( std::ostream&, BST& ).

Speaking of that operator:
* When does the loop end? The condition on line 3 should not change within the loop.
* Line 7 is never executed due to the return on line 6.


PS. Don't you ever have const Books or BST's to print? Surely the "print" operation does not modify the printed object?

[Kman]

It won't let me make the function that takes ( std::ostream&, Node* ) because it says that Node is undefined in my header file since I have to declare operators outside the standard class, even if I make it a friend.

[Peter87]

Use BST::Node to refer to the Node class outside of the BST class.

[Kman]

Got it. Thanks for the help, guys!