Re: [Boost-users] [units] - overriding output

Subject: Re: [Boost-users] [units] - overriding output
From: Noah Roberts (roberts.noah_at_[hidden])
Date: 2009-09-15 19:24:08

Matthias Schabel wrote:
>> What is the correct way to override the << op for a unit so that it 
>> say prints "Pa" instead of "m^-1 kg s^-2"?
>>
>> I tried this and no worky:
>>
>> #include <boost/units/io.hpp>
>>
>> namespace boost { namespace units {
>>
>>
>> template<>
>> inline std::string
>> name_string< boost::units::pressure_dimension, 
>> boost::units::si::system >(const boost::units::si::pressure&)
>> {
>>  return "Pa";
>> }
>>
>> }} // boost::units
> 
> "name_string" and "symbol_string" aren't templated - they are overloaded 
> functions, so the template is not correct. Also, you defined 
> "name_string", which is for fully-formatted unit output (e.g. "pascal" 
> vs. "Pa"), so you are overloading the wrong function here. The easy way 
> is to include the SI IO header : 
> 
> #include <boost/units/io.hpp>
> #include <boost/units/quantity.hpp>
> #include <boost/units/systems/si.hpp>
> #include <boost/units/systems/si/io.hpp>

Well, thanks.  Unfortunately although this works for every test program 
I can imagine that looks like my production code....it just plain 
doesn't in the actual code I'm trying to develop.  No matter what I do, 
it always prints out m^-1 kg s^-2 for the unit and no matter how I wrap 
up typedefs and usings inside my own namespace I can't reproduce the 
problem in simple code.  Some demon from the deepest pit of hell is 
keeping the overload resolution from working only in production code.