constant variables not working in header

Question

if I define my constant varibles in my header like this...

extern const double PI = 3.1415926535;
extern const double PI_under_180 = 180.0f / PI;
extern cons         


        

Answer 1

An old question, indeed, but one useful answer is missing.

It is possible to trick MSVC into accepting static constants in headers simply by wrapping those in a "dummy" class template:

template 
struct C {
     static const double Pi;
};

template 
const double C::Pi = 3.14159;

Now, C<>::PI can be accessed from elsewhere. No redefinition complains; constant is directly accessible in each compilation units without fancy link time optimization. Macro can be rolled out to further prettify this approach (even though macros are evil).