Initializing a reference variable in a class constructor

Question

So I'm still kind of figuring out the semantics of C++ references here.

I have a class that has a reference as a member, and I initialize the reference in the constructor.

template<class T>
class AVLNode {

private:
       T & data;
public:
       AVLNode(T & newData) {
            data = newData;
        }
};

But I get this error on the constructor line:

error: uninitialized reference member ‘AVLNode<int>::data’ [-fpermissive]

I don't get this, I initialize the reference as soon as the class is constructed so there shouldn't be a problem with the reference being uninitialized right?

not a duplicate, the answer provided to my question included a clear definition of initializer — Ethan, Jun 03 '13 at 02:43

score 23 · Accepted Answer · edited May 23 '17 at 12:24

23

Since data is a reference, you must initialize it at constructor initializer:

AVLNode(T & newData): data(newData) {

}

You may find this post useful: reference member variable must be initialized at constructor initialization list. You may also need to understand the difference between initialization and assignment when you write a class's constructor.

Quoting from C++ Primer pp455:

Some members must be initialized in the constructor initializer. For such members, assigning to them in the constructor body doesn't work. Members of a class type that do not have default constructor and members that are const or reference types must be initialized in the constructor initializer regardless of type.

edited May 23 '17 at 12:24

Community

1
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answered Jun 03 '13 at 00:53

taocp

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Very interesting. That works! My C++ book actually doesn't touch on these at all! THanks for your help – Ethan Jun 03 '13 at 00:58
5

If it actually doesn't mention member initialization list, burn that book. – Balog Pal Jun 03 '13 at 01:08
Damn you know I almost bought C++ Primer...but I bought C++ Primer Plus instead -_- – Ethan Jun 03 '13 at 01:08
if it mentions it...it isn't listed in the index... – Ethan Jun 03 '13 at 01:09

Initializing a reference variable in a class constructor

1 Answers1