Undefined reference error

[SoD]

I have the following class declared in a header file named calculation.h:

namespace Calc
{
template <class T, class E, class Q>
class Calculation
{
private:
T a;
E b;
Q result;

Q& add();
Q& sub();
Q& mul();
Q& div();

public:
Calculation(const T& first,const E& second) : a(first),b(second){};
Q& calculate(const char& op);
};
;
}

When I attempt to use the calculate function, I get the undefined reference error. It seems that the compiler doesn't recognize that the calculate function is implemented in the source file calculation.cpp, because if I copy the implantation into the header file for all the class functions, the error disappears.

Here is how I implemented it in the source file:
#include "calculation.h"
using namespace Calc;

/*****************************************************************/
template <class T, class E, class Q>
Q& Calculation<T, E, Q>::calculate(const char& op)
{
switch (op) {
case '+':
return add();
break;
case '-':
return sub();
break;
case '*':
return mul();
break;
case '/':
return div();
break;
default:
break;
}

}
/**********************************************************************/

Any one has any idea for how to fix it?

[LB]

Change the extension of the .c file to a .cpp file.

[SoD]

Sorry it's already cpp, wrote .c by accident in the original post =P

[Disch]

are you linking to calculation.cpp? Is it part of your project?

Oh durr.. it's a template.

You can't put template definitions in cpp files. the whole thing must go in your header.


(also... this is unrelated, but it seems strange that you're returning references everywhere)

[ne555]

There is an article about this, but I can't find it.
This is the idea:
You can't have a cpp if you work with templates. However if you want to have separate file with the implementation do this
#include "calculation.hpp" at the end of the header file (I change the extension)

[SoD]

Ok thanks for the answers =)

I return reference because so far I saw no reason not to. If I see that I return local values as reference I will change it.

[sohguanh]

Q& add();
Q& sub();
Q& mul();
Q& div();

I return reference because so far I saw no reason not to. If I see that I return local values as reference I will change it.

Not only that but by returning Q& that is reference to *this, you allow nested calls on your object.

Calculation calc;

calc.add().sub().mul().div();

Cool isn't it :)