Simple Objective C initialization

Pitfall · November 2008

As an assembly language and C programmer new to Objective C, I occasionally need an array of constants. This is easily created in C:

int list[5] = {1,2,3,4,5};

Is there a simple equivalent in Objective C?

Thanks for any help.

RickMaddy · November 2008

It's the same I believe.

PhoneyDeveloper · November 2008

You can of course use C-style arrays in Objective-C. I do that with constant arrays, where I build them at compile time and don't modify the contents, similar to the example you showed. You can put constant pointers to objects in them, of which the most likely, or maybe only, kind is NSString*

I also sometimes will use an NSArray or NSDictionary for the same purpose. I'll have an accessor that builds the NSArray/NSDictionary lazily. These objects have some advantages over C-style arrays.

Pitfall · November 2008

Pitfall here again... Armed with the comment that it should work I made some progress. I was trying to init the constant array in the interface declaration where I establish my globals. It doesn't let me populate the array there.

On the other hand, the C syntax works perfectly inside the implementation declaration, when used locally within a method.

I could use NSArray, but it seemed overkill to alloc a memory region, initWithObjects, and then have to purge - all to make a 10 byte table.

I guess it makes sense that Objective C won't let me embed a code-like construct in the declaration area. But being new to the language that didn't jump out at me.

Thanks for the replies.

PhoneyDeveloper · November 2008

A constant C-style array needs to be a file scope static or a function local variable. Normally a file scope static would be the way to do this. The static initialization can't go in a class declaration.

I wouldn't worry about overkill in generating an NSArray, unless you have proof that this will be a problem. Your most precious resource is your time. Development time spent tracking down bugs in use of C-Style arrays is wasted if those bugs can't exist if you use an NSArray.

squash · February 2009

ok so if i stored a static array of integers in a class in java, how would i do this in objective c. for example:

public class MyListClass
{
	public static final int list[] = {1,2,3,4,5};
}

which would be accessed by simply MyListClass.list.

exorcyze · February 2009


// in your .h
@interface MyListClass : NSObject {
    NSArray *list;
}
@property (nonatomic, retain) NSArray *list;

// in your .m
@synthesize list;
- (void) dealloc {
    [list release];
    [super dealloc];
}
// whereever you set it up ( init most likely ):
NSArray *temp = [[NSArray alloc] initWithObjects:[NSNumber numberWithInt:1], [NSNumber numberWithInt:2], [NSNumber numberWithInt:3], nil];
self.list = temp;
[temp release];

Pedro Valentini · February 2009

Realy a lof of code....

NSArray *list = [NSArray arrayWithObjects:[NSNumber numberWithInt:1], [NSNumber numberWithInt:2], [NSNumber numberWithInt:3], [NSNumber numberWithInt:4], [NSNumber numberWithInt:5], nil];

We need to use ruby in iphone...

In RUBY is:

list = [1,2,3,4,5]

MobileGeorge · January 2010

exorcyze;46337 said:


// in your .h
@interface MyListClass : NSObject {
    NSArray *list;
}
@property (nonatomic, retain) NSArray *list;

// in your .m
@synthesize list;
- (void) dealloc {
    [list release];
    [super dealloc];
}
// whereever you set it up ( init most likely ):
NSArray *temp = [[NSArray alloc] initWithObjects:[NSNumber numberWithInt:1], [NSNumber numberWithInt:2], [NSNumber numberWithInt:3], nil];
self.list = temp;
[temp release];

There is no need to create an array of NSNumber objects if you only want integer values.


// in your .h
@interface MyListClass : NSObject {
    const int *list;
}
@end

// in your .m
@implementation MyListClass
static const int constList[5] = {1, 2, 3, 4, 5};
...and in init:
list = constList;
@end

yoichi · February 2010

I had a similar problem as I am new to Objective-C. As others are saying, it is the same as the normal C but one difference. That is, you can use them as you expect, but not with Objective-C specific things.

I figured out that C variable initializers can be used in the class interface, too, but not between @interface and the {...} or within the "{...}".

Otherwise they can be declared as you do with normal C header files. They can be also declared outside the block surrounded by an @interface and the paring @end.

E.g. This is OK and the emptyCoordinate can be used in the @implementation:

@interface ...
{
 ...
}

static const CLLocationCoordinate2D emptyCoordinate = {-1.0, -1.0};

@property ...
...
...
@end

@implementation ...

@synthesize myCoord;

- (void)viewDidLoad
{
   myCoord = emptyCoordinate;
   ...
}

@end

Or:

static const CLLocationCoordinate2D emptyCoordinate = {-1.0, -1.0};
@interface ...
...
@end

Or:

- (void)viewDidLoad
{
   ...
   CLLocationCoordinate2D emptyLoc = {-1.0, -1.0};
   ...
}

Howdy, Stranger!

Forums

Simple Objective C initialization

Replies