Le lun 01/03/2004 à 01:06, Thorsten Ottosen a écrit :
namespace std {
#define CNAME( Var ) Var##_constant_t
#define OVERLOAD_CONTEXT( ConstType, FP, FPV ) \ inline FP operator+( FP l, ConstType ) \ { return l + FPV; } \ inline FP operator+( ConstType, FP r ) \ { return r + FPV; } \ inline FP operator-( FP l, ConstType ) \ { return l - FPV; } \ inline FP operator-( ConstType, FP r ) \ { return FPV - r; } \ inline FP operator*( FP l, ConstType ) \ { return l * FPV; } \ inline FP operator*( ConstType, FP r ) \ { return r * FPV; } \ inline FP operator/( FP l, ConstType ) \ { return l / FPV; } \ inline FP operator/( ConstType, FP r ) \ { return FPV / r; } \
#define DEFINE_FP_CONSTANT( Name, FV, DV, LDV ) \ struct CNAME( Name ) \ { \ CNAME( Name ) () {} \ operator float() const { return FV; } \ operator double() const { return DV; } \ operator long double() const { return LDV; } \ }; \ OVERLOAD_CONTEXT( CNAME( Name ), float, FV ) \ OVERLOAD_CONTEXT( CNAME( Name ), double, DV ) \ OVERLOAD_CONTEXT( CNAME( Name ), long double, LDV ) \ const CNAME( Name ) Name;
DEFINE_FP_CONSTANT( pi, 3.14F, 3.14232, 3.1423211223L )
} // namespace std
Unless I'm missing something, it seems to me that the constants can only be defined for built-in floating-point numbers. Indeed, once the structure for a pi constant has been defined by DEFINE_FP_CONSTANT (in the math_constant.hpp header), the user or others libraries cannot add new values for their own numerical types. With respect to that, I think the proposal of Daniel Frey is a lot more interesting since it allows user-defined types and provides automatic type deduction so that complex constants do not have to have their own names. Being able to write "interval<double> a = 2 * pi;" and being sure it is mathematically correct and accurate is great. Regards, Guillaume