如何创建类的全局常量-C ++

Question

I'm trying to create a class of complex number and want to create the imaginary unit i as constant. I want to be able to use it in any code when the class is included. For example :

#include "complex.h"
complex c = 2*i;

I've tried to define it that way : static const complex i in complex.h under public: and const complex complex::i = complex(0,1) in complex.cpp. But when I write the code on the top in main.cpp , I get undeclared variable error.

How can I do this?

Note : I've defined the = and * operators

Answer 1

Declare extern const complex i in complex.h .

If you do not declare i to be extern it must be defined in every compilation unit that uses it. Linking two such compilation units will then produce a duplicate definition error.

Answer 2

You declared complex::i but you are trying to use i . Either change your code to

complex c = 2 * complex::i;

Or create a global constant i (note: that's not a good idea; but you might do it inside a namspace).