wiiki - BoostUnits

One of the BoostLibraries

A brilliant example of the power of Static Typing. An extensible framework for compile-time dimensional analysis in C++ with no runtime overhead.

http://boost.org/libs/units

Example:

/// the ideal gas law in si units
template<class Y>
quantity<si::amount,Y> 
idealGasLaw(const quantity<si::pressure,Y>& P,
            const quantity<si::volume,Y>& V,
            const quantity<si::temperature,Y>& T)
{
    using namespace boost::units::si;

    #if BOOST_UNITS_HAS_TYPEOF 
    using namespace constants::codata;
    return (P*V/(R*T));
    #else
    return P*V/(8.314472*(joules/(kelvin*mole))*T);
    #endif // BOOST_UNITS_HAS_TYPEOF
},

Which is used as follows:

/// test ideal gas law
quantity<temperature>   T = (273.+37.)*kelvin;
quantity<pressure>      P = 1.01325e5*pascals;
quantity<length>        r = 0.5e-6*meters;
quantity<volume>        V = (4.0/3.0)*3.141592*pow<3>(r);
quantity<amount>        n(idealGasLaw(P,V,T));

Note that defining the base units is sufficient to use any plausible derived unit.