Force definition of symbol for a C++ template instance in a library

Question

I\'d like to provide a library that provides template code. But I would also like to keep the most possible the ownership of this code (generated code) when I can guess the

Answer 1

I would separate the implementation and the interface, using template specialization:

lib1.h:

#include 
template  void print_me(void);
template <> void print_me<0>(void);
template <> void print_me<1>(void);

lib1_internal.h (NOTE: this does not need to be disclosed):

#include 

template
void print_me_internal() {
    std::cout << "I am function number " << N << std::endl;
}

lib1.cpp:

#include "lib1.h"
#include "lib1_internal.h"

template <> void print_me<0>() {
  print_me_internal<0>();
}
template <> void print_me<1>() {
  print_me_internal<1>();
}

your main.cpp will correctly lead to a linker error:

$ g++ main.cpp -L. -l1
/tmp/ccZSDqkp.o: In function `main':
main.cpp:(.text+0xf): undefined reference to `void print_me<2>()'
collect2: ld returned 1 exit status

Just add the definition of template void print_me(void) in lib1.h in place of its declaration and it will be used whenever not found in the specialized versions.