运行后出现undefined reference to `operator<<(std::ostream&, Coordinate&)'的错误

----------遍历函数-----------------------------------------

template<typename T>
void MyStack<T>::stackTraverse(bool Transform)
{
 if(Transform)
 {
  for(int i = 0; i < m_iTop; i++)
  {
   cout<<m_pBuffer[i];
   //m_pBuffer[i].printCoordinate();
  }
 }
 else
 {
  for(int i = m_iTop-1; i >= 0; i--)
  {
   cout<<m_pBuffer[i];
   //m_pBuffer[i].printCoordinate();
  }
 }
 cout<<endl;
}

------------重载-------------------------

ostream& operator<<(ostream &out, Coordinate &coor)
{
 out<<"<"<<coor.m_iX<<","<<coor.m_iY<<">"<<endl;
 return out;
}