Templated function being reported as “undefined reference” during compilation

Question

These are my files:

--------[ c.hpp ]--------

#ifndef _C
#define _C

#include
class C
{
public:
    template void ca         


        

Answer 1

I believe this is because when you compile c.cpp the compiler doesn't know it needs to generate code for C::call(Merc&), and when you're compiling main.cpp it doesn't have the definition of C::call(T&) from which to instantiate C::call(Merc&).

Template definitions are essentially semantic macros, so much like the preprocessor's #define lexical macros they must be visible in the compilation units that use them.