Question

in foo.h:

#ifndef FOO_H
#define FOO_H

enum Rat
{
    A,
    B
};

class Foo
{
public:
    template<Rat r>
    int aMemberFunc(int, int, int);
};

#endif

in foo.cpp:

#include "foo.h"

namespace {
template<Rat r>
int helper(int a, int b)
{
    return a+b*((int) r);
}
}

template<Rat r>
int Foo::aMemberFunc(int a, int b, int c)
{
    return a + helper<r>(b,c);
}

in main.cpp:

#include "foo.h"
#include <iostream>

using namespace std;

int main(void)
{
    Foo test;
    cout << test.aMemberFunc<B>(1,2,3) << endl;
}

I compile with g++ main.cpp foo.cpp and I get:

main.cpp:(.text+0x88): undefined reference to `int Foo::aMemberFunc<(Rat)1>(int, int, int)'
collect2: ld returned 1 exit status

I would prefer not to move stuff to the header because that brings along the helper and a lot of baggage, I tried to add a file fooimpl.cpp:

#include "foo.h"
#include "foo.cpp"

template int Foo::aMemberFunc<A>(int,int,int);
template int Foo::aMemberFunc<B>(int,int,int);

and then compile with g++ fooimpl.cpp main.cpp foo.cpp

This was per the suggestion of Dietmar (thanks!) but as soon as I add a function void rand(); in the header of foo.h and void rand() {} in foo.cpp the above trick yields this error:

foo.cpp:(.text+0x0): multiple definition of `Foo::rand()’
/tmp/ccoCtGMk.o:fooimpl.cpp:(.text+0x0): first defined here

how do i work around this?

Answer 1

You need to instantiate your function, not specialize it:

#include "foo.h"
#include "foo.cpp"

template int Foo::aMemberFunc<A>(int,int,int);
template int Foo::aMemberFunc<B>(int,int,int);