Thread: [Dev-C++] templates + linker error

i have 3 source  calc.h calc.cpp and principal.cpp (i compilated it with
devcpp)

i have this error:
In function `main':
[Linker error] undefined reference to `calc<double>::multiply(double,
double)'
ld returned 1 exit status
[Build Error] ["Proyecto] Error 1

somebody could help me please :)

/********calc.h******/
#ifndef _CALC_H
#define _CALC_H

template <class A_Type> class calc
{
public:
A_Type multiply(A_Type x, A_Type y);
A_Type add(A_Type x, A_Type y);

};

#endif

/****calc.cpp******/
#include "calc.h"
#include <iostream>
using namespace std;

template <class A_Type> A_Type calc<A_Type>::multiply(A_Type x,A_Type y)
{
return x*y;
}
template <class A_Type> A_Type calc<A_Type>::add(A_Type x, A_Type y)
{
return x+y;
}


/******principal.cpp*****/
#include "calc.h"
#include <iostream>
#include <cstdlib>

using namespace std;

int main()
{
calc <double> a_calc_class;
double a, b;
a=4.3;
b=3.4;
a_calc_class.multiply(a,b);

system("PAUSE");
return EXIT_SUCCESS;
}
/***************************/

The reason for the error is you are not passing the obj file of calc.cpp
to the linker. Make appropriate settings in DevCpp. I think, you have to
add calc.cpp to your project. Sorry I dont use DevCpp.


On Sun, 2008-05-25 at 16:42 -0500, Jorge Guevara wrote:
> 
> i have 3 source  calc.h calc.cpp and principal.cpp (i compilated it
> with devcpp)
> 
> i have this error:
> In function `main':
> [Linker error] undefined reference to `calc<double>::multiply(double,
> double)'
> ld returned 1 exit status
> [Build Error] ["Proyecto] Error 1
> 
> somebody could help me please :)
> 
> /********calc.h******/
> #ifndef _CALC_H
> #define _CALC_H
> 
> template <class A_Type> class calc
> {
> public:
> A_Type multiply(A_Type x, A_Type y);
> A_Type add(A_Type x, A_Type y);
> 
> };
> 
> #endif
> 
> /****calc.cpp******/
> #include "calc.h"
> #include <iostream>
> using namespace std;
> 
> template <class A_Type> A_Type calc<A_Type>::multiply(A_Type x,A_Type
> y)
> {
> return x*y;
> }
> template <class A_Type> A_Type calc<A_Type>::add(A_Type x, A_Type y)
> {
> return x+y;
> }
> 
> 
> /******principal.cpp*****/
> #include "calc.h"
> #include <iostream>
> #include <cstdlib>
> 
> using namespace std;
> 
> int main()
> {
> calc <double> a_calc_class;
> double a, b;
> a=4.3;
> b=3.4;
> a_calc_class.multiply(a,b);
> 
> system("PAUSE");
> return EXIT_SUCCESS;
> }
> /***************************/
> 
> 
> -------------------------------------------------------------------------
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> Defy all challenges. Microsoft(R) Visual Studio 2008.
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Think a bit about it.

What code to you suggest that the compiler should enerate when it compiles
calc.cpp? If the compiler does not know that other source files will use
the template parameter "double", how will the compiler then be able to add
a "double" version of multiply when it compiles calc.cpp?

Remember that it is the compiler, not the linker, that produces the
runnable code. The linker will have no use for an object file that doesn't
contain instantiated template functions.

/pwm

On Mon, 26 May 2008, Lloyd wrote:

> The reason for the error is you are not passing the obj file of calc.cpp
> to the linker. Make appropriate settings in DevCpp. I think, you have to
> add calc.cpp to your project. Sorry I dont use DevCpp.
>
>
> On Sun, 2008-05-25 at 16:42 -0500, Jorge Guevara wrote:
> >
> > i have 3 source  calc.h calc.cpp and principal.cpp (i compilated it
> > with devcpp)
> >
> > i have this error:
> > In function `main':
> > [Linker error] undefined reference to `calc<double>::multiply(double,
> > double)'
> > ld returned 1 exit status
> > [Build Error] ["Proyecto] Error 1
> >
> > somebody could help me please :)
> >
> > /********calc.h******/
> > #ifndef _CALC_H
> > #define _CALC_H
> >
> > template <class A_Type> class calc
> > {
> > public:
> > A_Type multiply(A_Type x, A_Type y);
> > A_Type add(A_Type x, A_Type y);
> >
> > };
> >
> > #endif
> >
> > /****calc.cpp******/
> > #include "calc.h"
> > #include <iostream>
> > using namespace std;
> >
> > template <class A_Type> A_Type calc<A_Type>::multiply(A_Type x,A_Type
> > y)
> > {
> > return x*y;
> > }
> > template <class A_Type> A_Type calc<A_Type>::add(A_Type x, A_Type y)
> > {
> > return x+y;
> > }
> >
> >
> > /******principal.cpp*****/
> > #include "calc.h"
> > #include <iostream>
> > #include <cstdlib>
> >
> > using namespace std;
> >
> > int main()
> > {
> > calc <double> a_calc_class;
> > double a, b;
> > a=4.3;
> > b=3.4;
> > a_calc_class.multiply(a,b);
> >
> > system("PAUSE");
> > return EXIT_SUCCESS;
> > }
> > /***************************/
> >
> >
> > -------------------------------------------------------------------------
> > This SF.net email is sponsored by: Microsoft
> > Defy all challenges. Microsoft(R) Visual Studio 2008.
> > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
> > _______________________________________________ Dev-cpp-users mailing list Dev...@li... TO UNSUBSCRIBE: http://www23.brinkster.com/noicys/devcpp/ub.htm https://lists.sourceforge.net/lists/listinfo/dev-cpp-users
>
>
> ______________________________________
> Scanned and protected by Email scanner
>
> -------------------------------------------------------------------------
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
> _______________________________________________
> Dev-cpp-users mailing list
> Dev...@li...
> TO UNSUBSCRIBE: http://www23.brinkster.com/noicys/devcpp/ub.htm
> https://lists.sourceforge.net/lists/listinfo/dev-cpp-users
>

The compiler can't create the code for a template function unless it sees
the implementation when you try to use the template function.

You should have the implementation of your multiply function in the header
file, and not hidden in a cpp file.

It is only the linker that will see the generated code from multiple cpp
files, and neither the compiler nor the compiler knows that calc.cpp
should create a specific version of the multiply function with the double
data type.

/pwm

On Sun, 25 May 2008, Jorge Guevara wrote:

> i have 3 source  calc.h calc.cpp and principal.cpp (i compilated it with
> devcpp)
>
> i have this error:
> In function `main':
> [Linker error] undefined reference to `calc<double>::multiply(double,
> double)'
> ld returned 1 exit status
> [Build Error] ["Proyecto] Error 1
>
> somebody could help me please :)
>
> /********calc.h******/
> #ifndef _CALC_H
> #define _CALC_H
>
> template <class A_Type> class calc
> {
> public:
> A_Type multiply(A_Type x, A_Type y);
> A_Type add(A_Type x, A_Type y);
>
> };
>
> #endif
>
> /****calc.cpp******/
> #include "calc.h"
> #include <iostream>
> using namespace std;
>
> template <class A_Type> A_Type calc<A_Type>::multiply(A_Type x,A_Type y)
> {
> return x*y;
> }
> template <class A_Type> A_Type calc<A_Type>::add(A_Type x, A_Type y)
> {
> return x+y;
> }
>
>
> /******principal.cpp*****/
> #include "calc.h"
> #include <iostream>
> #include <cstdlib>
>
> using namespace std;
>
> int main()
> {
> calc <double> a_calc_class;
> double a, b;
> a=4.3;
> b=3.4;
> a_calc_class.multiply(a,b);
>
> system("PAUSE");
> return EXIT_SUCCESS;
> }
> /***************************/
>

I try with this. and no problem

#include <iostream>
#include <cstdlib>
#include "mypair.hpp"
#include "mypair.cpp"   // i include the implementation in the source
principal.cpp

the question is less efficient?, or its ok?

bytes


2008/5/26, Per Westermark <pw...@ia...>:
>
> The compiler can't create the code for a template function unless it sees
> the implementation when you try to use the template function.
>
> You should have the implementation of your multiply function in the header
> file, and not hidden in a cpp file.
>
> It is only the linker that will see the generated code from multiple cpp
> files, and neither the compiler nor the compiler knows that calc.cpp
> should create a specific version of the multiply function with the double
> data type.
>
> /pwm
>
>
> On Sun, 25 May 2008, Jorge Guevara wrote:
>
> > i have 3 source  calc.h calc.cpp and principal.cpp (i compilated it with
> > devcpp)
> >
> > i have this error:
> > In function `main':
> > [Linker error] undefined reference to `calc<double>::multiply(double,
> > double)'
> > ld returned 1 exit status
> > [Build Error] ["Proyecto] Error 1
> >
> > somebody could help me please :)
> >
> > /********calc.h******/
> > #ifndef _CALC_H
> > #define _CALC_H
> >
> > template <class A_Type> class calc
> > {
> > public:
> > A_Type multiply(A_Type x, A_Type y);
> > A_Type add(A_Type x, A_Type y);
> >
> > };
> >
> > #endif
> >
> > /****calc.cpp******/
> > #include "calc.h"
> > #include <iostream>
> > using namespace std;
> >
> > template <class A_Type> A_Type calc<A_Type>::multiply(A_Type x,A_Type y)
> > {
> > return x*y;
> > }
> > template <class A_Type> A_Type calc<A_Type>::add(A_Type x, A_Type y)
> > {
> > return x+y;
> > }
> >
> >
> > /******principal.cpp*****/
> > #include "calc.h"
> > #include <iostream>
> > #include <cstdlib>
> >
> > using namespace std;
> >
> > int main()
> > {
> > calc <double> a_calc_class;
> > double a, b;
> > a=4.3;
> > b=3.4;
> > a_calc_class.multiply(a,b);
> >
> > system("PAUSE");
> > return EXIT_SUCCESS;
> > }
> > /***************************/
> >
>
>


-- 
Ing. Jorge Luis Guevara Diaz
Bs Ciencias de la Computacion
Maestrante en Ciencia de la Computación
http://jorge.sistemasyservidores.com   http://inf.unitru.edu.pe/~jlgd
Escuela de Informática - Universidad Nacional de Trujillo
Escuela de Ingeniería de Sistemas - Universidad Privada del Norte

Always avoid including cpp files. cpp files are indented to generate
object files and be linked.

Templated functions are intended to be compiled into object files first
when needed. As I wrote in one of my earlier mails, template functions
should be placed in the relevant header file.

Look at the STL files: In all cases, the actual source code
for the implementations of lists, trees, arrays etc are available in the
header files.

/pwm

On Tue, 27 May 2008, Jorge Guevara wrote:

> I try with this. and no problem
>
> #include <iostream>
> #include <cstdlib>
> #include "mypair.hpp"
> #include "mypair.cpp"   // i include the implementation in the source
> principal.cpp
>
> the question is less efficient?, or its ok?
>
> bytes
>
>
> 2008/5/26, Per Westermark <pw...@ia...>:
> >
> > The compiler can't create the code for a template function unless it sees
> > the implementation when you try to use the template function.
> >
> > You should have the implementation of your multiply function in the header
> > file, and not hidden in a cpp file.
> >
> > It is only the linker that will see the generated code from multiple cpp
> > files, and neither the compiler nor the compiler knows that calc.cpp
> > should create a specific version of the multiply function with the double
> > data type.
> >
> > /pwm
> >
> >
> > On Sun, 25 May 2008, Jorge Guevara wrote:
> >
> > > i have 3 source  calc.h calc.cpp and principal.cpp (i compilated it with
> > > devcpp)
> > >
> > > i have this error:
> > > In function `main':
> > > [Linker error] undefined reference to `calc<double>::multiply(double,
> > > double)'
> > > ld returned 1 exit status
> > > [Build Error] ["Proyecto] Error 1
> > >
> > > somebody could help me please :)
> > >
> > > /********calc.h******/
> > > #ifndef _CALC_H
> > > #define _CALC_H
> > >
> > > template <class A_Type> class calc
> > > {
> > > public:
> > > A_Type multiply(A_Type x, A_Type y);
> > > A_Type add(A_Type x, A_Type y);
> > >
> > > };
> > >
> > > #endif
> > >
> > > /****calc.cpp******/
> > > #include "calc.h"
> > > #include <iostream>
> > > using namespace std;
> > >
> > > template <class A_Type> A_Type calc<A_Type>::multiply(A_Type x,A_Type y)
> > > {
> > > return x*y;
> > > }
> > > template <class A_Type> A_Type calc<A_Type>::add(A_Type x, A_Type y)
> > > {
> > > return x+y;
> > > }
> > >
> > >
> > > /******principal.cpp*****/
> > > #include "calc.h"
> > > #include <iostream>
> > > #include <cstdlib>
> > >
> > > using namespace std;
> > >
> > > int main()
> > > {
> > > calc <double> a_calc_class;
> > > double a, b;
> > > a=4.3;
> > > b=3.4;
> > > a_calc_class.multiply(a,b);
> > >
> > > system("PAUSE");
> > > return EXIT_SUCCESS;
> > > }
> > > /***************************/
> > >
> >
> >
>
>
> --
> Ing. Jorge Luis Guevara Diaz
> Bs Ciencias de la Computacion
> Maestrante en Ciencia de la Computación
> http://jorge.sistemasyservidores.com   http://inf.unitru.edu.pe/~jlgd
> Escuela de Informática - Universidad Nacional de Trujillo
> Escuela de Ingeniería de Sistemas - Universidad Privada del Norte
>