Can't figure what's causing this error.

[Croolsby]

Some background information:

I'm using SFML 1.6 in Code::Blocks 10.05
I'm trying to create a function that will do something to a sf::Vector2<T>.
I want to put this functions declaration in a .hpp separate from the main function, and it's implementation in a separate .cpp file.

Here is the bare minimum of what I am trying to do:

main.cpp

#include <SFML/Graphics.hpp>
#include "A.hpp"

int main()
{
	sf::Vector2<int> v;
	foo(v);
}

A.hpp

#include <SFML/Graphics.hpp>

template <typename T>
void foo(sf::Vector2<T>&);

A.cpp

#include "A.hpp"

template <typename T>
void foo(sf::Vector2<T>&)
{

}

Here is the compile error in Code::Blocks 10.05

obj\Debug\main.o||In function `main':|
C:\...\main.cpp|7|undefined reference to `void foo<int>(sf::Vector2<int>&)'|
||=== Build finished: 1 errors, 0 warnings ===|

What does undefined reference mean? I thought it meant the function is not implemented, or it can't find the implementation of the declaration. Looks like it should work though.

[hamsterman]

Template functions need to be implemented in headers (visible to whatever is using them).

[Croolsby]

Ok, that fixed it. Thanks.