constexpr replacements for math constants like M_PI

Question

Are there any C++11 constexpr constants which can be used instead of the constant macros from <cmath>, i.e. constants like M_PI and friends? Or lacking that, any global const values which provide these constants at runtime?

Answer 1

There are no predefined constexpr or global const constants defined in C++ standard library. But you can define them by yourself like, for example:

namespace MathConstants {
    const double E =            2.71828182845904523536;
    const double LOG2E =        1.44269504088896340736;
    const double LOG10E =       0.434294481903251827651;
    const double LN2 =          0.693147180559945309417;
    const double LN10 =         2.30258509299404568402;
    const double PI =           3.14159265358979323846;
    const double PI_2 =         1.57079632679489661923;
    const double PI_4 =         0.785398163397448309616;
    const double PI_1_PI =      0.318309886183790671538;
    const double PI_2_PI =      0.636619772367581343076;
    const double PI_2_SQRTPI =  1.12837916709551257390;
    const double SQRT2 =        1.41421356237309504880;
    const double SQRT1_2 =      0.707106781186547524401;
};

Or use boost math constant templates, some documentation here (haven't used it).