(Thanks to Jason Merrill for this section).
g++ does not automatically instantiate templates defined in other files. Because of this, code written for cfront will often produce undefined symbol errors when compiled with g++. You need to tell g++ which template instances you want, by explicitly instantiating them in the file where they are defined. For instance, given the files
`templates.h':
template <class T>
class A {
public:
void f ();
T t;
};
template <class T> void g (T a);
`templates.cc':
#include "templates.h"
template <class T>
void A<T>::f () { }
template <class T>
void g (T a) { }
main.cc:
#include "templates.h"
main ()
{
A<int> a;
a.f ();
g (a);
}
compiling everything with g++ main.cc templates.cc will result in
undefined symbol errors for `A<int>::f ()' and `g (A<int>)'. To
fix these errors, add the lines
template class A<int>; template void g (A<int>);
to the bottom of `templates.cc' and recompile.