Question

I have this error:

Undefined symbols for architecture x86_64:
  "my::Queue<int>::Queue()", referenced from:
      _main in ccdwI88X.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status

for this code ‘main.cpp’:

#include "Queue.hpp"

int main()
{
  my::Queue<int> myqueue;
  return 0;
}

‘Queue.hpp’:

#ifndef QUEUE_HH__
#define QUEUE_HH__

namespace my
{
  template <typename T>
  class Queue
  {
  public:
    Queue();     
  };
}

#endif

and ‘Queue.cpp’:

#include "Queue.hpp"

template <typename T>
my::Queue<T>::Queue() 
{
}

Answer 1

The answer posted here: https://stackoverflow.com/a/312402/700926 is what I think you need.

If I edit your Queue.cpp file to this:

#include "Queue.hpp"

template <typename T>
my::Queue<T>::Queue() 
{

}

template class my::Queue<int>;

.. it compiles fine.

For the detailed explanation, please consult the URL i mentioned at first.