CODEWITHSUNDEEP
c++visual-studioc++11
LNK
LNK

Reputation: 191

MSVC 2015 cannot compile constexpr atan

I have used Mingw-w64 compiler in my project. Now I am compiling the project with MSVC2015. The following line gives an error:

constexpr double pi = 4*std::atan(1);

error:

error: C2131: expression did not evaluate to a constant

However it compiled in mingw without any problems.

Upvotes: 1

Views: 1205

Answers (1)

Rakete1111
Rakete1111

Reputation: 48998

MSVC is right in this case, from [constexpr.functions]p1

This document explicitly requires that certain standard library functions are constexpr. An implementation shall not declare any standard library function signature as constexpr except for those where it is explicitly required.

As you can see from the last sentence that I highlighted, an implementation is not allowed to declare a function constexpr if the standard doesn't say so.

Now does the standard say that atan is constexpr? No, as can be seen from the signature in [c.math]:

float atan(float x);  // see [library.c]
double atan(double x);

Upvotes: 3

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