Question

I’m using Android NDK r6 and Android SDK API 8 (2.2).

I’m trying to implement a dynamic list like std::vector using templates but I get plenty of errors in the compiled .o files.

A sample:

As you can see the errors are produced in the compiled .o files, not in source files.

Class definition:

template <class T>
class ArrayList{
    private:
        int mSize;

    public:
        /**
         * Construye una lista dinámica vacía.
         */
        ArrayList ();

        /**
         * Destructor.
         */
        ~ArrayList ();

        /**
         * Añade un elemento a la lista.
         *
         * @param element
         *              Elemento.
         */
        void add (T element);

        /**
         * Obtiene un elemento de la lista.
         *
         * @param index
         *              Índice del elemento. Rango válido de valores: [0, size()]
         * @return Elemento de la posición indicada o NULL si el índice no es válido.
         */
        T get (int index);

        /**
         * Elimina un elemento de la lista.
         *
         * @param index
         *              Índice del elemento. Rango válido de valores: [0, size()]
         */
        void remove (int index);

        /**
         * Vacía la lista.
         */
        void clear ();

        /**
         * Consulta el número de elementos de la lista.
         *
         * @return Número de elementos.
         */
        int size ();

        /**
         * Consulta si la lista esta vacía.
         *
         * @return true si está vaía, sinó false.
         */
        bool isEmpty ();
};

Class implementation:

template <class T>
ArrayList<T>::ArrayList (){
    mSize = 0;
}

template <class T>
ArrayList<T>::~ArrayList (){

}

template <class T>
void ArrayList<T>::add (T element){

}

template <class T>
T ArrayList<T>::get (int index){
    T element;
    return element;
}

template <class T>
void ArrayList<T>::remove (int index){

}

template <class T>
void ArrayList<T>::clear (){

}

template <class T>
int ArrayList<T>::size (){
    return mSize;
}

template <class T>
bool ArrayList<T>::isEmpty (){
    return true;
}

Class usage:

ArrayList<OtherClass> list;
OtherClass foo;
list.add (foo);

Answer 1

It’s template code. You don’t have the same header file to cpp file relationship like a normal C++ class. I generally restructure it like so:

Foo.h:

#ifndef FOO_H
#define FOO_H

template <class T>
class Foo
{
    Foo();
};

// Note that the header file INCLUDES the cpp file. This is simply to maintain
// the general .h .cpp file structure, but adapt it to template code, where the
// implementation is supposed to be in the header file and is not compiled.
#include "Foo.cpp"

#endif

Foo.cpp:

// Note that I do NOT include the header here. Also, do NOT compile this file.
// So if you have a makefile, be sure not to include this file in it.
template <class T>
Foo<T>::Foo()
{ }

Or you can just stick the entire implementation in the header file and not have a cpp file at all. This would actually make more sense because you do NOT compile the cpp file. Read more here.