multiple definition of operator<< ?

[Thorsten Gecks]

Hello, I'm programming a bigger project and recently I tried to print a
simple internal type on cout. For this reason I wrote and operator<< for
the simple type:

ifndef KSIMONSTRUCTS_HH
#define KSIMONSTRUCTS_HH

#include <utility>
#include <ostream.h>

namespace KSimoN {

struct DocUnitPosition
{
  int x;
  int y;
  int z;
};

}  // End of namespace


ostream & operator<<(ostream & os, const KSimoN::DocUnitPosition & pos)
{
  return os << '(' << pos.x << ',' << pos.y << ',' << pos.z << ')';
}

#endif




Now, here is my problem:                              ###########

Compiling my programm, I get the following error:

/home/student/programmieren/ksimon/ksimon/view2dnormalzplane.h(.text+0x0):
multiple definition of `operator<<(ostream &,
KSimoN::DocUnitPosition const &)'
view2dnormalnormalunit.o(.text+0x0):/usr/include/g++-3/stl_alloc.h:
first defined here
collect2: ld returned 1 exit status



I don't understand that, since I do define this operator only in the file
printed above. (I'm using Mandrake 7.1 and got libstdc++-devel from their
ftp-server.) Here is in addition view2dnormalzplane.h:

ifndef KSIMONVIEW2DNORMALZPLANE_H
#define KSIMONVIEW2DNORMALZPLANE_H

#include <memory>
#include <qwidget.h>
#include <qobjectlist.h>

#include <structs.h>             // this file contains the struct and the
                                 // operator<<   ######################

#include <view2dnormalabstractbase.h>


namespace KSimoN {

class View2DNormalZPlane : public QWidget, public View2DNormalAbstractBase
{
  Q_OBJECT

public:

  View2DNormalZPlane( QWidget * parent, const char * name, int wflags,
                     DocUnitLocator * unitLocatorArg = 0);

  ~View2DNormalZPlane();

  bool drawLink(View2DAbstractUnit * source, View2DAbstractUnit * target)
                  { return true; }  // not implemented yet


protected:

  auto_ptr<QObjectList> selectedChilds(const QRect & selection) const;

private:

  void placeUnits(pair<DocUnitPosition, DocUnitPosition> &
                         minMaxOfNetwork);

};

} // End of namespace

#endif