Linker error for an undefined reference to a constructor

[Tozar]

 Error: [Linker error] undefined reference to `Node<QA>::Node(QA)'

Im writing a basic program for an animal guessing game (similar to twenty questions) using a binary search tree. The project consists of a lot of header files, so things are bound to get messy. But this is one error I haven't been able to figure out.

Here's the function I've narrowed the problem down to:

    bool QATree::insert(string o, bool q)
    {
       Node<QA>* newnode = new Node<QA>(QA(o,q)); // this constructor function call causes the error.
       if (!root)
       {
          root = newnode;
          return true;
       }
       if (insert(root, newnode));  
          return true;    
    }

...And the seperate .cpp file for the Node class (it's friended to QATree).

    #include "bsttools.h"
    template <typename T>
    Node<T>::Node(T s)
    {
        data = s;
        left = NULL;
        right = NULL;
    }

If you have any questions, or can't see the error here and would like to see more code, I'll be glad to help you help me.

[hk_mp5kpdw]

All templated code must be placed in the header files that are included in all the various source files that use the templated class. You cannot split them, the templated class, up into seperate header and source files like you would do with non-templated classes.

[King Mir]

You can split them, but only if you #include the .cpp file in the .h file.

Actually there are other ways too, but this is most common.

[hk_mp5kpdw]

You can split them, but only if you #include the .cpp file in the .h file.

Actually there are other ways too, but this is most common.

You REALLY should not get in the habit of including source files!

[King Mir]

You REALLY should not get in the habit of including source files!

You can call it an .hpp file if you want. The idea is to create symetry with classes, and sepetate the implementation from the class declaration.

Having a teplate is a sourse file only makes the compiler create an empty .o file. No real harm done.

[Tozar]

Thank you very much! I had doubted that anyone could understand my problem, because even my computer science teacher was stumped. I'll definately come back to this forum next time I need help.

[Dave_Sinkula]

You and your teacher may want to become familiar with C++ FAQ LITE, starting here.