[Boost-users] Order of composite units in the output

Subject: [Boost-users] Order of composite units in the output
From: Esben Mose Hansen (boost_at_[hidden])
Date: 2009-02-18 06:09:55

Hi,

I think I am beginning to get the boost:units library, but I still have one 
problem. Consider:

#include <iostream>
#include <boost/units/io.hpp>
#include <boost/units/systems/si/length.hpp>
#include <boost/units/make_system.hpp>
#include <boost/units/quantity.hpp>
#include <boost/units/base_dimension.hpp>
#include <boost/units/base_unit.hpp>
#include <boost/units/derived_dimension.hpp>

// Introduce slot (measured in e.g. ffe or tfe) as a basic dimension, unit and 
in a system
struct slot_base_dimension :
    boost::units::base_dimension<slot_base_dimension, 1>
{ };
typedef slot_base_dimension::dimension_type slot_dimension;

struct ffe_base_unit : public boost::units::base_unit<ffe_base_unit, 
slot_dimension, 1>
{
    static std::string name()   { return("40ft equivalent"); }
    static std::string symbol() { return("ffe"); }
};

typedef ffe_base_unit::unit_type slot_t;
BOOST_UNITS_STATIC_CONSTANT(ffe, slot_t);

/// derived dimension (slot) flow
typedef 
boost::units::derived_dimension<slot_base_dimension,1,boost::units::time_base_dimension,-1>::type 
flow_dimension;

/// placeholder class defining si unit system
typedef boost::units::make_system<boost::units::si::meter_base_unit,
                                  boost::units::si::second_base_unit,
                                  ffe_base_unit>::type unit_system;

typedef boost::units::unit<flow_dimension,unit_system>  flow_t;
BOOST_UNITS_STATIC_CONSTANT(ffe_per_second, flow_t);

int main() {
  boost::units::quantity<flow_t> flow(4*ffe_per_second);
  std::cout << "flow= " << flow << std::endl;
}

This program outputs
flow= 4 s^-1 ffe

which is correct, but a bit unusual... 4 ffe/s or even 4 ffe s^-1 would have 
been better. Is this possible?

Thanks!

-- 
kind regards, Esben