Where do you declare a constant in Objective-C?

Question

I declared a constant in a header file const double EARTH_RADIUS=6353; that is imported to various other headers and I got a linker error.

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Answer 1

You can declare in the header, define it in a code file. Simply declare it as

extern const double EARTH_RADIUS;

then in a .m file somewhere (usually the .m for the .h you declared it in)

const double EARTH_RADIUS = 6353;