Problem Instantiating Template Class in C++

Nibbie

Posts: 1
Joined: 2008.10

Post: #1

Nov 17, 2008 — 06:41 AM

Hey there guys,

I am having some trouble creating an instance of a C++ template that I wrote.
It sounds simple and I have no idea why this is happening, but when i try to do:

Code:

    using namespace DataStructure;

    BinarySearchTree<int> testTree;

I get this error from Xcode:

Code:

"DataStructure::BinarySearchTree<int>::~BinarySearchTree()", referenced from:

      _main in main.o

  "DataStructure::BinarySearchTree<int>::BinarySearchTree()", referenced from:

      _main in main.o

ld: symbol(s) not found

collect2: ld returned 1 exit status

It looks like it can't find the constructor/destructor when it gets created, although i can't imagine why, because it definately exists.

Here is a sample of my code incase anyone can help:

from BinarySearchTree.h:

Code:

namespace DataStructure

{

    template <typename Type>

    class BinarySearchTree : public DataStructure::BinaryTree<Type>::BinaryTree

    {

    public:

        BinarySearchTree();

        ~BinarySearchTree();

        bool Search        ( const Type &searchItem ) const;

        void Insert        ( const Type &insertItem );

        void DeleteNode    ( const Type &deleteNode );

    private:

        void deleteFromTree( BSNode<Type> *&p );

    };

}

from BinarySearchTree.cpp:

Code:

template <typename Type>

DataStructure::BinarySearchTree<Type>::BinarySearchTree()

{

}

template <typename Type>

DataStructure::BinarySearchTree<Type>::~BinarySearchTree()

{

}

The help would be greatly appreciated.
This has been driving me insane for hours.
Thanks everyone

mattz

Member

Posts: 45
Joined: 2006.07

Post: #2

Nov 17, 2008 — 09:19 AM

For templated classes, don't use a separate .cpp file. Put it *all* in the header. When you compile the .cpp, it doesn't instantiate the template for any particular class unless you tell it to by adding the line

Code:

template class DataStructure::BinarySearcyTree<int>;

at the end of the file. If you know you only want to instantiate the template for a few specific classes, this is okay, but generally you want everything in the header file.

bmantzey

Member

Posts: 241
Joined: 2008.07

Post: #3

Jan 13, 2009 — 11:54 PM

Trivia: there's actually a keyword that works on some compilers (none mainstream) export, which somehow allows you to separate the implementation of a template class.

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