Hi Robert, Robert Ramey wrote:
I have a program in which there is the notion of consumption rate such as m^3/sec, gallons/hour, etc.
I have consumption_rate unit defined in terms of si units. I read in a quanity in gallons/hour and so far so good. If I display the quantity it is displayed as m^3/sec. This displays the "compound units" as expected - very cool. All this is OK as far as it goes. When I try to display the quantity as gallons/hour again I have a whole host of problems. The attached test fill illustrates the issues. The only way I've been able to do is is by making a complete end run around the units system itself - sort of self defeating.
I would appreciate insight anyone might be able to offer into this issue.
It's a little confusing, but it's printing in the si units because consumption_rate_unit is generated from the si::system. You can create your own system with volume and time and create the consumption rate from it. The following shows how: #include <iostream> #include <boost/units/io.hpp> #include <boost/units/pow.hpp> #include <boost/units/systems/cgs.hpp> #include <boost/units/systems/si.hpp> #include <boost/units/systems/si/io.hpp> #include <boost/units/base_units/metric/hour.hpp> #include <boost/units/base_units/us/gallon.hpp> using namespace boost::units; // derive special units that we use in our application // derived dimension for consumption_rate : M T^-1 typedef boost::units::derived_dimension< boost::units::length_base_dimension,3, boost::units::time_base_dimension,-1
::type consumption_rate_dimension;
typedef boost::units::make_system<us::gallon_base_unit, metric::hour_base_unit>::type consumption_system; typedef unit< consumption_rate_dimension, consumption_system
consumption_rate_unit;
typedef quantity<consumption_rate_unit, float> consumption_rate; typedef unit<volume_dimension, consumption_system> gallon_unit; BOOST_UNITS_STATIC_CONSTANT(gallon, gallon_unit); BOOST_UNITS_STATIC_CONSTANT(gallons, gallon_unit); typedef unit<time_dimension, consumption_system> hour_unit; BOOST_UNITS_STATIC_CONSTANT(hours, hour_unit); BOOST_UNITS_STATIC_CONSTANT(hour, hour_unit); int main() { quantity<consumption_rate_unit> C(1.0 * gallon / hour); std::cout << 1.0 * gallons / hour << " - ok displays gal/hour" << std::endl; std::cout << C << " - ok displays gal/hour" << std::endl ; return 0; } HTH, Nate