Fails:

.h:
namespace IBDS
{
public:
		friend Vector3D operator ^ (const Vector3D& a, const Vector3D& b);
}

.cpp:
Vector3D IBDS::operator ^ (const Vector3D& a, const Vector3D& b)
{
	return Vector3D ( 	a.v[1]*b.v[2] - a.v[2]*b.v[1],
				a.v[2]*b.v[0] - a.v[0]*b.v[2],
				a.v[0]*b.v[1] - a.v[1]*b.v[0]);
};


=> /ibds/Math/Vector3D.cpp:204: error: 'IBDS::Vector3D IBDS::operator^(const IBDS::Vector3D&, const IBDS::Vector3D&)' should have been declared inside 'IBDS'


This works:
.h:
namespace IBDS
{
public:
	friend Vector3D operator ^ (const Vector3D& a, const Vector3D& b)
	{
		return Vector3D ( 	a.v[1]*b.v[2] - a.v[2]*b.v[1],
				a.v[2]*b.v[0] - a.v[0]*b.v[2],
				a.v[0]*b.v[1] - a.v[1]*b.v[0]);
	};
}

.cpp:
// nil