template member functions in a non template class

I am working on an assignment and this problem has me puzzled. I am still working on working on template functions. Mostly within classes. I am seeking help on where my error is. Here is my code.

In my class header I have:

class predator
{
public:

template<typename t>
void hunt(t & prey);
// other stuff...

private:
// more stuff
}

In my definition I have this:

template <typename t>
void predator::hunt(t & prey)
{
// what I want it to do here
}

And to use the function I have something like:

predatorName.hunt(preyName);


Now when I compile (I have been using Dev c++) I get the following error:

Linker error: Undefined reference to 'void predator::hunt<predator>(predator&)'

Any hints on what I am doing wrong. Thanks very much in advance.

Kat

Should work, so it could be a lot of things. The best you could do is break it down to the smallest example, and see if it works. If it doesn't, you could always post your COMPLETE code.

Code:

---

class predator
{
public:
    template<typename t>
    void hunt(t& prey);
};

template <typename t>
void predator::hunt(t& prey)
{
}


int main()
{
    predator pred;
    int a = 5;
    pred.hunt(a);
}

---

This works no problem for me.

With templates, you cant split the code into .h and .cpp files like you can with non-templates without export which virtually no compiler supports, or ever will, though comeau does.

When you include the .h in a file and try to use the templated function, the compiler tries to instantiate the template substituting the generic type(s) for specific type(s) but it cannot do that unless it can see the definition of the template.

Post implementation of void predator::hunt(t & prey).

Or alternative way is to do it in OO way, have a base class Prey and inherit from it different kind of preys and have void predator::hunt(Prey& prey)

Well, some good news and some bad.

If I just declare the function and its definition it compiles. However as soon as I use it, I get the linker error.

For example the part where you have:

int main()
{
predator pred;
int a = 5;
pred.hunt(a);
}

I get the linker error again. But, just creating the function and not using it yet, does not cause an error.

Quote:

---

Originally Posted by Russco

With templates, you cant split the code into .h and .cpp files like you can with non-templates without export which virtually no compiler supports, or ever will, though comeau does.

When you include the .h in a file and try to use the templated function, the compiler tries to instantiate the template substituting the generic type(s) for specific type(s) but it cannot do that unless it can see the definition of the template.

---

This must be the issue. Thanks for this information. Frustrating since the instructor wants us to do it this way. Class header and class .cpp file. And I am using the templated function in another class .cpp file, for example I have a world class that uses the predator class. All different files of course.
ie. predator.h, predator.cpp, world.h, world.cpp

In the .h put the class dec and the template definition. in the class.cpp file put the non-template definitions. In the main.cpp file include the .h and use your class. it should work fine.