How to declare constexpr extern?

Question

Is it possible to declare a variable extern constexpr and define it in another file?

I tried it but the compiler gives error:

De

Answer 1

What you probably want is extern and constexpr initialization, e.g.:

// in header
extern const int g_n;

// in cpp
constexpr int g_n = 2;

This is support though in Visual Studio 2017 only through conformance mode:

• /Zc:externConstexpr (Enable extern constexpr variables)
• constexpr definition of extern const variable