How to create global functions in Objective-C

Question

I'm developing an iphone app and I need to have some functions to use globally in my classes.

But how can I do this?

I just tried to create functions.h likes this

#include <Foundation/Foundation.h>  - (void)printTest; 

and in the functions.m

#import "functions.h"  - (void)prinTest {     NSLog(@"test"); } 

but it doesn't work. Says me: "Method definition not in a @implementation context".

Answer 1

When you want a global function, just write a regular C function. The Objective-C syntax is meant to be used solely in the context of object methods.

void printTest() {     NSLog(@"This is a test"); } 

You also have to add the declaration in the functions.h header:

void printTest(); 

Answer 2

First note that Objective-C language is a superset of C language (meaning there is absolutely nothing wrong with mixing them).

There are two approaches.

#1 Real global function:

Declare a global C-style function, which can have ObjC logic (in definetion instead of just C-style logic).

Header:

void GSPrintTest(); 

Implementation:

#import "functions.h"  #import <Foundation/Foundation.h>  void GSPrintTest() {   NSLog(@"test"); } 

Call using:

#import "functions.h" ... GSPrintTest(); 

A third (bad, but possible) option would be adding a category to NSObject for your methods:

Header:

#import <Foundation/Foundation.h>  @interface NSObject(GlobalStuff) - (void) printTest; @end 

Implementation:

#import "functions.h"  @implementation NSObject(GlobalStuff) - (void) printTest {   NSLog(@"test"); } @end 

Call using:

#import "functions.h" ... [self printTest]; 

#2 class method:

Create a class method with + sign, in helper class (instead of instance method with - sign).

Header:

#import <Foundation/Foundation.h>  @interface GlobalStuff : NSObject {}  + (void)printTest;  @end 

Implementation:

#import "functions.h"  @implementation GlobalStuff  + (void) printTest {   NSLog(@"test"); }  @end 

Call using:

#import "functions.h"  ... [GlobalStuff printTest];