Tuesday Coding Tip 15 — Mathematical constants in C++

Question

Tuesday coding tips are super short posts about various tidbits mainly from C++, but also from other programming languages I use. You can also follow the #TuesdayCodingTips hashtag on Mastodon and LinkedIn.

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Since C++20, you can include header <numbers> and use many commonly used, precomputed mathematical constants like Pi, Phi, square root of 2 and 3, natural logarithms of 2 and 10, and many more! Even better, you can choose their precision by specifying the underlying type via a template.

And since C++17, the <cmath> header contains some special math functions I’ve never heard of like cylindrical Bessel functions, associated Legendre polynomials, or Riemann zeta function.

#include <iostream>
#include <numbers>
#include <iomanip> // std::setprecision
#include <limits> // std::numeric_limits

template<typename T>
void printConstant(T value)
{
    const auto default_precision{std::cout.precision()};

    std::cout << std::setprecision(std::numeric_limits<T>::digits10 + 1);
    std::cout << value << std::endl;

    std::cout << std::setprecision(default_precision);
}

int main()
{
    using namespace std::numbers;
    printConstant(pi_v<float>);
    printConstant(pi_v<double>);
    printConstant(pi_v<long double>);

    /* Outputs:
    3.141593
    3.141592653589793
    3.141592653589793239
    */
}

• Constants are documented here: https://en.cppreference.com/w/cpp/numeric/constants
• Special functions are documented here: https://en.cppreference.com/w/cpp/numeric/special_functions