C++ Template Programming Question

templates must be defined in header files - you cant declare them in header and then define them in cpp files.

This has to do with how templates work. Consider the following:

template
T Helper::compare(T a, T b)
{
if (a < b) return a;
return b;
}


Now, when the compiler sees the following in main.cpp:
int a = 10;int b = 50;
Helper::compare(a, b);

generates a function(without you being aware of it ofcourse):

int Helper::compare(int a,int b)
{
if (a < b) return a;
return b;
}

if, further along the code, sees:
string sa="Hello";string sb="World";
Helper::compare(sa,sb);

generates another function:

string Helper::compare(string a,string b)
{
if (a < b) return a;
return b;
}

When all needed functions have been generated inside main.cpp, it is finally compiled.

In order to do all that, the compiler must know the implementation of the templated function. Since the compilation of .cpp files is done individually, and since you have put the implementation in helper.cpp, it has no way of knowing that when it compiles main.cpp . In other words, the easiest way to fix this would be to put both the declaration and the definition inside the helper.h.

Cool, thanks guys, I managed to get it work now.

I've create a helper.inl to put the implementation inside and have it included as part of the helper.h header file.

I still want to hide the implementation some how, very much like creating inline functions hehz.

Perfect. Thanks again.

You can implement templates in source code and call them from other files.

You just need to use the explicit template specifier:
template<>


// Aside:
by the way, when quoting source code, use [sou_rce] and [/sou_rce] (replace sou_rce with source) tags and you get:




// Back to the Topic:

// Helper.cpp


Try the above. I'm killing time at work and don't have a compiler to test it on sorry. - You may have to declare the functions before defining them, which might not make this very useful. You might also need typename before the "int Helper" or "char Helper". Can't remember right now.