templates and operator overloading

[st-man]

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

[NMTop40]

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


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?)

[st-man]

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


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