CODEWITHSUNDEEP
c++tree
smatter
smatter

Reputation: 29178

Dealing with trees of different node types

I am having a tree data structure that can have different types of nodes deriving from one TreeBaseNode class. I have made the tree nodes of type TreeBaseNode * which gets assigned to objects of different Special nodes at run time. How can I access aNodeAttribute from the TreeBaseNode* pointer while traversing the tree on the tree is generated (if the node is of type SpecialNodeA which I can identify from NodeType)

class TreeBaseNode
{
public:
    int NodeType;   
    TypeA commonNodeAttributeA,
    TypeB commonNodeAttributeB; 
};

class SpecialNodeA : public TreeBaseNode
{
private:

    TypeD aNodeAttribute

public:
    SpecialNodeA(int type)
    {
        NodeType = type;
    }
    //Methods   
};

class SpecialNodeB : public TreeBaseNode
{

private:

    TypeE bNodeAttribute;

public:
    //Methods


};

EDIT: changed the types

Upvotes: 2

Views: 2760

Answers (3)

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272467

Based on the extra information in the comments, why not add a public virtual int estimate() = 0; to the base class (assuming that the result of the estimation is an int), and override it in the derived classes? i.e. tie the estimation specialisations to the specialised classes. That way, you don't have to deal with polymorphic code to extract the type-specific fields.

Upvotes: 0

Timo Geusch
Timo Geusch

Reputation: 24341

An alternative to Mihran's suggestion would be to use dynamic_cast<> to cast those nodes that you know are of type SpecialNodeA from TreeBaseNode down into a SpecialNodeA and then just call an appropriate member function to retrieve the attribute you're after.

In this particular scenario you can even do away with the NodeType member in the base class as a dynamic_cast<SpecialNodeA> on a node that isn't of this type will simply return a null pointer. I'm not too fond of hierarchies where the base class has to have knowledge of its derived types as that does away with some of the benefits of a class hierarchy and tends to suggest the design isn't as clean as it should be.

Upvotes: 2

Mihran Hovsepyan
Mihran Hovsepyan

Reputation: 11088

There is no polymorphism of data-members of clases in c++, but you can use polymorphism of function-members. So you should declare virtual int getNodeAttribute(){} in your base class. And reimplement it in two Derived classes to return attribute what you want.

Upvotes: 4

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