在Objective-C中定义全局常量

// Constants.h
#ifndef Constants_h
#define Constants_h

extern NSString *const kGlobalConstant;

#endif /* Constants_h */

// Constants.m
#import "Constants.h"

NSString *const kGlobalConstant = @"This is a global constant";

#import "Constants.h"

- (void)someMethod {
    NSLog(@"%@", kGlobalConstant);
}