28 Numerics library [numerics]

28.8 Numbers [numbers]

28.8.2 Mathematical constants [math.constants]

The library-defined partial specializations of mathematical constant variable templates are initialized with the nearest representable values of e, , , π, , , ln2, ln10, , , , the Euler-Mascheroni γ constant, and the golden ratio φ constant , respectively.
Pursuant to [namespace.std], a program may partially or explicitly specialize a mathematical constant variable template provided that the specialization depends on a program-defined type.
A program that instantiates a primary template of a mathematical constant variable template is ill-formed.