Objective C Macro append to string

Question

I think this is a very simple thing to do, but since I'm new to iOS development and objective C, I can't figure it out.

#define RESTFUL_PATH_PREFIX @"https://gogch.com/gch-restful";
#define LOGIN RESTFUL_PATH_PREFIX @"/login;

I want the result "https://gogch.com/gch-restful/login"

but I'm getting the result as "https://gogch.com/gch-restful"

other topics in stackoverflow mention only about adding a new string to the beginning of a string like,

#define DOMAIN "example.com"
#define SUBDOMAIN "test." DOMAIN

score 4 · Accepted Answer · answered Jun 05 '15 at 10:29

Remove the trailing semi-colon:

#define RESTFUL_PATH_PREFIX @"https://gogch.com/gch-restful";
                                                            ^

and then string constants can be concatenated by the compiler:

@"first" @"second"

instead of:

@"first"; @"second"

tailec · Answer 2 · 2015-06-05T11:01:14.223

2

It is much better practice to use constants instead of define macros.

static NSString *const YourPath = @"https://...";

And then you can concatenate your strings with NSString stringWithFormat: method.

edited Jun 05 '15 at 11:01

answered Jun 05 '15 at 10:59

tailec

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@Droppy You can benefit type safety. – tailec Jun 05 '15 at 11:03
1

That's not true; the compiler will soon tell you if you try and concatenate a string and non-string type. – Droppy Jun 05 '15 at 11:04
2

@Droppy you're right about this. This [answer](http://stackoverflow.com/a/17228508/4482445) explains why it is better. – tailec Jun 05 '15 at 11:10
It's not that it's "better" per-say, it's just more declarative. For what it's worth, I've worked with frameworks making use of both paradigms. Rule of thumb: do what the framework does. If you're making a new framework, pick one paradigm and stick with it. You'll get a teeny bit more debugging features with constants ... that's all I can think of. – Sean Sep 22 '16 at 16:03

score 0 · Answer 3 · edited Jun 20 '20 at 09:12

Since I made this answer to a question marked as a dupe, I'll also answer it here

Sure, you can use defines OR you can use NSString constants. It's really a matter of preference ... I have however seen both a #define and an NSString const * const being used before. Defines are easier, and you're probably not going to save that much memory by having constants instead of individual immutable instances of NSString all over the place.

Some advice is to think about how you export the NSString constants. You'll probably want EXTERN_PRIVATE instead of EXTERN, but my sample code will allow all clients of your header to read the string constants you've declared therein.

What you can do:

Create a new .m/.c file with a header in Xcode
In the .m/.c file, declare and initialise your constants
Export the constant as necessary so other compilation units can access it

constants.h

#ifndef constants_h
#define constants_h

// Export the symbol to clients of the static object (library)
#define EXTERN extern __attribute__((visibility("default")))
// Export the symbol, but make it available only within the static object
#define EXTERN_PRIVATE extern __attribute__((visibility("hidden")))
// Make the class symbol available to clients
#define EXTERN_CLASS __attribute__((visibility("default")))
// Hide the class symbol from clients
#define EXTERN_CLASS_PRIVATE __attribute__((visibility("hidden")))
#define INLINE static inline

#import <Foundation/Foundation.h>

EXTERN NSString const * _Nonnull const devBaseUrl;

#endif /* constants_h */

constants.m

#include "constants.h"

NSString const * _Nonnull const devBaseUrl = @"http://127.0.0.1:8000/";

main.m

#import <Foundation/Foundation.h>
#import "constants.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSLog(@"Constant value: %@", devBaseUrl);
        // Prints: Constant value: http://127.0.0.1:8000/
    }
    return 0;
}

Objective C Macro append to string

3 Answers3

What you can do:

constants.h

constants.m

main.m

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