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

15 Sep 2009

      ...
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 
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 
#include 
#include 
#include 

#include <iostream>

using namespace boost::units;

int main(void)
{
	std::cout << name_format << 1.0*si::pascal << std::endl
	          << symbol_format << 1.0*si::pascal << std::endl;
}

giving

1 pascal
1 Pa

The default output formatter is symbol format. Your code, with fixes  
of the bugs above, works as well :

#include 
#include 

namespace boost {
	namespace units {

	inline std::string symbol_string(const si::pressure&)
	{
		return "Pa";
	}
}
} // boost::units

#include <iostream>

using namespace boost::units;

int main(void)
{
	std::cout << 1.0*si::pascal << std::endl;
}

HTH,

Matthias

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

Matthias Schabel