Error in creating template class - c++

Question

I found this vector template class implementation, but it doesn't compile on XCode.
Header file:
// File: myvector.h
#ifndef _myvector_h
#define _myvector_h
template <typename ElemType>
class MyVector
{
public:
MyVector();
~MyVector();
int size();
void add(ElemType s);
ElemType getAt(int index);
private:
ElemType *arr;
int numUsed, numAllocated;
void doubleCapacity();
};
#include "myvector.cpp"
#endif
Implementation file:
// File: myvector.cpp
#include <iostream>
#include "myvector.h"
template <typename ElemType>
MyVector<ElemType>::MyVector()
{
arr = new ElemType[2];
numAllocated = 2;
numUsed = 0;
}
template <typename ElemType>
MyVector<ElemType>::~MyVector()
{
delete[] arr;
}
template <typename ElemType>
int MyVector<ElemType>::size()
{
return numUsed;
}
template <typename ElemType>
ElemType MyVector<ElemType>::getAt(int index)
{
if (index < 0 || index >= size()) {
std::cerr << "Out of Bounds";
abort();
}
return arr[index];
}
template <typename ElemType>
void MyVector<ElemType>::add(ElemType s)
{
if (numUsed == numAllocated)
doubleCapacity();
arr[numUsed++] = s;
}
template <typename ElemType>
void MyVector<ElemType>::doubleCapacity()
{
ElemType *bigger = new ElemType[numAllocated*2];
for (int i = 0; i < numUsed; i++)
bigger[i] = arr[i];
delete[] arr;
arr = bigger;
numAllocated*= 2;
}
If I try to compile as is, I get the following error:
"Redefinition of 'MyVector::MyVector()'"
The same error is displayed for every member function (.cpp file).
In order to fix this, I removed the '#include "myvector.h"' on the .cpp file, but now I get a new error:
"Expected constructor, destructor, or type conversion before '<' token".
A similar error is displayed for every member as well.
Interestingly enough, if I move all the .cpp code to the header file, it compiles fine. Does that mean I can't implement template classes in separate files?

Answer 1

It's always a good idea to place your templates in a header file. That way you don't mess up the linker with multiple definitions of the same instantiations and such.
And of course there's the circular inclusion :).

Answer 2

First, you have
#include "myvector.cpp"
which creates a circular reference between the files. Just get rid of it.
The other problem is that you are defining a template class inside a .cpp file. Template definitions are only allowed inside header files. There may be ways around that, but for g++ (which XCode uses) that's how the cookie crumbles.