Constants in Objective-C and “duplicate symbol” linker error

问题

I've declared a constant with the same name in some different classes, in their .m file, this way:

@implementation MyViewController
const NSInteger numberOfItems = 6;
...
@end

But I get a "duplicate symbol" error when trying to build the project. I've found several posts dealing with this issue regarding extern or global constants, but what I'd want is just declaring some constants private to their class, how can I do that?

Thanks

回答1:

If you want to use constant only in one .m file then declare it as static. For example:static NSString * const CONSTANT_STRING = @"Constant I am".

In case of NSInteger you can write in your every .m file:

static const NSInteger my_const = 3;

If you want globals (one constant with one value visible in every file) then write in your .h:

extern const NSInteger my_global_const;

and in your .m file you can add

const NSInteger my_global_const = 5;

来源：https://stackoverflow.com/questions/17145223/constants-in-objective-c-and-duplicate-symbol-linker-error