Accessing member function from inherited class template

Question

I have a class template A which looks like this:

A.h

template <typename T>
class A
{
  T data;

  public:
  A(void) { };
  ~A(void) { };

  void addItem(T d);
}

A.cpp

template <typename T>
void A<T>::addItem(T data)
{

};

And another class template B which looks like this:

B.h

#include "a.h"
class B : public A<int>
{
   public:
   B(void) : A<int>() {};
   ~B(void) {};

   void doSomething();
};

B.cpp

#include "B.h"

void B::doSomething()
{
   addItem(1);
}

When compiling this under VS 2012 I get an error which says:

error LNK2019: unresolved external symbol "public: void __thiscall A::addItem(int)" (?addItem@?$A@H@@QAEXH@Z) referenced in function "public: void __thiscall B::doSomething(void)" (?doSomething@B@@QAEXXZ)

Why isn't the addItem() member function resolvable? Can you please recommend a way to fix this?

This has been asked a million times. Do you not search? http://stackoverflow.com/a/12574417/560648 — Lightness Races in Orbit, Jan 02 '14 at 01:49
@LightnessRacesinOrbit you really don't need to act all smug. — horatiu, Jan 06 '14 at 16:55
@user12748: Instructing you to search is not "acting all smug". — Lightness Races in Orbit, Jan 06 '14 at 17:47
@LightnessRacesinOrbit: Well then, if this is strictly instructing, then how about you try to trim the unneeded parts where you are just being condescendent or expressing judgements. — horatiu, Jan 06 '14 at 20:07
@user12748: *sigh* I have done neither. I merely asked you to search before posting another duplicate. You don't need to get so defensive about it. I'm outta here. — Lightness Races in Orbit, Jan 06 '14 at 20:08

score 2 · Accepted Answer · answered Jan 02 '14 at 01:52

2

You need to move the content of A.cpp into A.h since C++ is very finicky about templates not being defined in headers.

answered Jan 02 '14 at 01:52

norlesh

1,749
11
23

@jogojapan is the rewording more appropriate? – norlesh Jan 02 '14 at 01:57
1

@jogojapan cheers - have a good day 7;^) – norlesh Jan 02 '14 at 01:58
1

C++ couldn't care less whether you define your function templates in headers or not. It just wants a definition in each translation unit, which is pretty reasonable when you consider that template instantiation is performed during compilation, not linking. – Lightness Races in Orbit Jan 02 '14 at 02:03
@Lightness Races in Orbit, would you like to explain to the question poster what constitutes a translation unit? – norlesh Jan 02 '14 at 02:05
@LightnessRacesinOrbit I see where your coming from, I just feel it appropriate to word the answer to the level of the question – norlesh Jan 02 '14 at 02:20
I feel it appropriate not to coddle site contributors. He will encounter terms he doesn't recognise all throughout his career, and now is a perfect time to learn to go and research them. Not to mention the topic is _fully_ covered on the two duplicates linked in the question's comments... – Lightness Races in Orbit Jan 02 '14 at 02:21

Accessing member function from inherited class template

1 Answers1