for field in mystruct.orderedFields
  stream.write(field.size, field.value);

C++ (Qt)
class bit_field_base;
 
class bit_record
{
public:
  void reg_field( bit_field_base *field ) { assert( field ); m_orderedFields.push_back( field ); }
 
private:
  std::list<bit_field_base*>  m_orderedFields;
};
 
class bit_field_base
{
public:
  bit_field_base( bit_record &record ) { record.reg_field( this ); }
}
 
 
// =================================================
 
class DataRecord : public bit_record
{
public:
  DataRecord() : m_fld1( *this ), m_fld2( *this ), m_fld3( *this ) {}
 
private:
  bit_field<1> m_fld1;
  bit_field<2> m_fld2;
  bit_field<3> m_fld3;
};
 

C++ (Qt)
  struct record
  {
    bit_field<1> flag;
    bit_field<4> mode;
    bit_field<9> address;
 
    bit_array pack() const
    {
      return ::pack( flag, mode, address );
    }
 
    static record  unpack( const bit_array &src )
    {
      record result;
      ::unpack( src, result.flag, result.mode, result.address );
      return result;
    }
  };