class ifstream_pos_returner
  {
    ifstream&  ifs;
    unsigned old_pos;
    public:
      ifstream_pos_returner( ifstream& infs , unsigned pos ) : ifs( infs ) , old_pos( pos )
      {
      }
      void reset( unsigned pos )
      {
        old_pos = pos;
      }
      ~ifstream_pos_returner()
      {
        ifs.seekg( old_pos , std::ios::beg );
      }
  };
...
spOneObject OneObject::load( ifstream& ){
  ifstream_pos_returner ret( ifs , ifs.tellg() );
  spOneObject res;
  ...
  if( something goes wrong)
    return res;
  ...
  ret.reset( ifs.tellg() );
  return res;
}