An example of Objective C Global constant - shows class definition, implementation, import and usage

obj_c_constant_class_impl.c

//Configuration.h

#import <Foundation/Foundation.h>

@interface Configuration : NSObject

extern NSString *const kRMAWebServiceURL;

extern const NSTimeInterval kRMTimeoutValue;

@end

//Configuration.m
#import "Configuration.h"

@implementation Configuration

NSString *const kRMAWebServiceURL = @"http://mywebservice.com";

const NSTimeInterval kRMTimeoutValue = 90;

@end

// AppName-Prefix.pch

// ... //

#ifdef __OBJC__
    #import <UIKit/UIKit.h>
    #import <Foundation/Foundation.h>
    #import "Configuration.h"
#endif

// ... //


/*
 * Usage
 */

// Afile.m

- (void)aMethodThatDoesSomething
{

    NSLog(@"%@", kRMAWebServiceURL);
    NSLog(@"%f", kRMTimeoutValue);

}