Question

I want to access class InternalNode’s getSurplus() method.

I have getSurplus() defined in a “InternalNode.h” file.

“…” means other code.

How do I refer to the method getSurplus from the InternalNode class?

//InternalNode.h
{
class InternalNode:public BTreeNode

{
 ...

 void remove(int a);
 int getSurplus() const;
 ...
 }

}



int InternalNode::getSurplus() const
{
 return (count - (internalSize + 1) / 2);
}

//
BTreeNode* InternalNode::remove(int value)
{
...

if (children[i]->getSurplus() >= 0) return SURPLUS; //Not correct syntax

...
}

Answer 1

Since children is an array of BtreeNode* objects, and InternalNode is derived from BtreeNode, then provided that the pointer returned from children[i] is in-fact a pointer to a InternalNode object (and not some other derived object of BtreeNode), you have to explicitly cast the pointer back to a type InternalNode*. This could be done like so:

if (static_cast<InternalNode*>(children[i])->getSurplus() >= 0)

If you are not sure that each BtreeNode* is pointing to an InternalNode object (i.e., it could be pointing to some other derived type), then you’re going to have to use a dynamic_cast<InternalNode*>(children[i]), and check to make sure the operation returns a valid pointer, and not NULL.

So if you’re absolutely sure about the types in your array, then you can use static_cast<>() in this situation (i.e., right now BtreeNode is the only base-class of InternalNode, it is not a virtual base class, etc.) … otherwise if you want to be safe at the cost of some run-time overhead, use dynamic_cast<>() and check for a NULL pointer return value from the cast operation.