templates and operator overloading

Hello,

I'am trying to write my own vector class. It is implemented using templates and operator overloading.

In ordern to allow vector addition this global method is implemented

template<typename T>
CVector3D<T> operator+( const CVector3D<T> &v1, const CVector3D<T> &v2 )
{
return( CVector3D<T>( v1._x + v2._x, v1._y + v2._y, v1._z + v2._z ) );
}


In the class definition I define this method as a friend of it,

template<typename T>
class CVector3D
{
public:

friend CVector3D<T> operator+( const CVector3D<T> &, const CVector3D<T> & );
...

but the linking process fails with

if g++ -DHAVE_CONFIG_H -I. -I/home/sschmidt/Develop/vectors/src -I.. -O0 -g3 -MT vectors.o -MD -MP -MF ".deps/vectors.Tpo" -c -o vectors.o /home/sschmidt/Develop/vectors/src/vectors.cpp; \
then mv -f ".deps/vectors.Tpo" ".deps/vectors.Po"; else rm -f ".deps/vectors.Tpo"; exit 1; fi
In file included from /home/sschmidt/Develop/vectors/src/vectors.cpp:29:
/home/sschmidt/Develop/vectors/src/cvector3d.h:62: Warnung: »friend«-Deklaration »CVector3D<T> operator+(const CVector3D<T>&, const CVector3D<T>&)« deklariert eine Nicht-Template-Funktion
/home/sschmidt/Develop/vectors/src/cvector3d.h:62: Warnung: (wenn das nicht beabsichtigt war, sollte sicher gestellt werden, dass das Funktions-Template bereits deklariert wurde, und <> hier hinter Funktionsnamen einfügen) -Wno-non-template-friend schaltet diese Warnung aus)
/bin/sh ../libtool --tag=CXX --mode=link g++ -O0 -g3 -o vectors vectors.o
g++ -O0 -g3 -o vectors vectors.o
vectors.o(.text+0x1b5): In function `main':
/home/sschmidt/Develop/vectors/src/vectors.cpp:49: undefined reference to `operator+(CVector3D<float> const&, CVector3D<float> const&)'
collect2: ld returned 1 exit status


This is probably related to an earlier warning

Warning: »friend« declaration »CVector3D<T> operator+(const CVector3D<T>&, const CVector3D<T>&)« declares a non-template-function
Warning: (if this was not intended you should make sure the function template is already declared and add <>
after the name of the function ) -Wno-non-template-friend switches this warning off

Adding
class CVector3D<T>;
CVector3D<T> operator+( const CVector3D<T> &, const CVector3D<T> & );

before the class definition in order to declare the method does not help either.
Does anyone knows what to do?

The following should work:

CVector3D<float> v1, v2, v3;

...

v3 = v1 + v2;


Kind regards,

Sven Schmidt

It's the old template-friend problem. operator+ is a template function. So the order is:

Code:

---

template < typename T > class CVector3D;

template < typename T >
 CVector3D<T> operator+( const CVector3D<T>, const CVector3D<T> );

template < typename T >
class CVector3D
{
    friend CVector3D operator+ <> ( const CVector3D< const CVector3D );
// etc.
};

template < typename T >
 CVector3D<T> operator+( const CVector3D<T>, const CVector3D<T> )
{
  // implement it here
}

---

By the way I've never heard of a 3-dimensional vector. (Surely it's a 3D matrix?)

Quote:

---

Originally Posted by NMTop40

It's the old template-friend problem. operator+ is a template function. So the order is:

Code:

---

template < typename T > class CVector3D;

template < typename T >
 CVector3D<T> operator+( const CVector3D<T>, const CVector3D<T> );

template < typename T >
class CVector3D
{
    friend CVector3D operator+ <> ( const CVector3D< const CVector3D );
// etc.
};

template < typename T >
 CVector3D<T> operator+( const CVector3D<T>, const CVector3D<T> )
{
  // implement it here
}

---

By the way I've never heard of a 3-dimensional vector. (Surely it's a 3D matrix?)

---

Thank you very much, seems I was close to solving the problem myself :-)
The vectors live in 3 dim. space, that's what I meant.

Thanks again, Sven