Does C++11, 14, 17 or 20 introduce a standard constant for pi?

Question

There is a rather silly problem with the number pi in C and C++. As far as I know M_PI defined in math.h is not required by any standard.

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Answer 1

Up to C++20, no, none of the standards introduces the constant that would represent the number pi (π). You can approximate the number in your code:

constexpr double pi = 3.14159265358979323846;

Other languages such as C# have the constant declared in their libraries.

Update: Starting with the C++20, there indeed is a pi constant declared inside the header. It is accessed via: std::numbers::pi.