C++Talk.NET

LaBird · Guest

Hi,

I have a simple question about templates.

When I have a class definition like this in "class.h":

template <typename T>
class C {
T p;
public:
void set(T);
void print(T);
};

And then I implement the member functions in "class.cpp":

#include "class.h"

template <typename T>
void C<T>::set(T t) {
// some meaningful stuff, setting p = t
}

template <typename T>
void C<T>::print(T t) {
// other meaningful stuff, printing out p
}

Now I would like to use the class in main() in "main.cpp".
How should I call it? I tried the following:

#include "class.h"

int main() {
C<int> object;
object.set(7);
// ...
return 0;
}

But when I compile with "g++ class.cpp main.cpp",
I get "undefined reference" for the C<T>::set(T) function
in main.cpp. How to overcome this, apart from merging
class.cpp and main.cpp together?

Thanks in advance.

Regards,
LaBird (Benny).

Josephine Schafer · Guest

"LaBird" <kellily (AT) excite (DOT) com> wrote

Peter van Merkerk · Guest

"LaBird" <kellily (AT) excite (DOT) com> :

Agent Mulder · Guest

LB> I would like to use the class in main() in "main.cpp".
LB> How should I call it?

Stick to this style and you'll never
have any problems with your #include's.

//This is file C.h. All headers needed go to main.cpp
template<typename T>class C
{
T p;
public:
void set(T t){p=t;}
void print(T t){cout<<"nif it ain't got that swing";}
};

//This if file Music.h. All headers needed go to main.cpp
class Music{};

//This is file Jazz.h. All headers needed go to main.cpp
class Jazz:public C
//This is file main.cpp. All #include's go here
#include <iostream.h>
#include "C.h"
#include "Music.h"
#include "Jazz.h"
int main(int argv,char**argc)
{
C<int>object;
object.set(7);
Jazz jazz;
jazz.print(*new Music);
return 0;
}

-----------------------------------
output

if it ain't got that swing

LaBird · Guest

Josephine Schafer <jsf (AT) usa (DOT) net> wrote

LaBird · Guest

Thank you very much, I did not realize before that my question is actually
not as simple as I thought to be. :)

Regards,
LaBird (Benny).

Peter van Merkerk <merkerk (AT) deadspam (DOT) com> wrote

Harald Grossauer · Guest

Josephine Schafer wrote:

Josephine Schafer · Guest

"LaBird" <kellily (AT) excite (DOT) com> wrote

Agent Mulder · Guest

LB> A follow-up question: As my actual class definiton is more complicated,
LB> and the member functions of the class contain lots of accesses to global
LB> variables, which are initialized at the global scope, something like:
LB>
LB> unsigned int count = 0;
LB> template<typename T> class C<T>::set(T t) {
LB> if (count % 2 == 0)
LB> p = t;
LB> else
LB> p = 0 - t;
LB> count++;
LB> }
LB>
LB> Can I put all these code into the .h as well?

Yes, that's my style. When I work on global
instances of my objects, I create the objects at the start
of the .h file and declare the class or template that
works on the global instances right under it.
The objects are encapsulated, not at class level
but at module (file) level. Works fine.

-X