在cpp文件中实现非模板类的模板成员

Question

I have a class:

// A.h
class A
{
    void foo();
    template <class T> void bar( T someVar );
}

#include "A.tcpp"

When I build it, I get linker errors. However, if the whole class would be a template, then the above example would build perfectly fine. So my question is:

How do I stick to the pattern of having ALL definitions in the cpp file, when having template member functions as opposed to having a template class?

Answer 1

If you are going to split aa class that has template functions and non template functions into a header file and a tcpp file then you only put the template definitions in the tcpp file. The non template definitions still needs to go into a regular cpp file.

Putting the non template code in the tcpp file includes it back into the header file and then that means it gets defined in every translation unit it gets included into.

In this case that means you should have

// A.h
class A
{
    void foo();
    template <class T> void bar( T someVar );
}

#include "A.tcpp"

// A.tcpp
template <class T> void A::bar( T someVar ) { some code; }

// A.cpp
#include "A.h"

void A::foo() { some code; }

Answer 2

I found the solution, it is not as nice as I would like, but it will do in my case. We can insert the following line at the end of the tcpp file:

template void A::bar<int>( int );
// And so on, for all types that should be supported.

It is called function template instantiation .