CODEWITHSUNDEEP
objective-c
dontWatchMyProfile
dontWatchMyProfile

Reputation: 46310

How to use a C array as instance variable?

For example I want to store this in an ivar:

CGFloat color[4] = {red, green, blue, 1.0f};

so would I put this in my header?

CGFloat color[];

How would I assign values to that guy later? I mean I can't change it, right?

Upvotes: 1

Views: 2422

Answers (3)

JeremyP
JeremyP

Reputation: 86651

Instance variables are zeroed out on allocation so you can't use initialisers with them.

You need something like this:

// MyObject.h

@interface MyObject
{
    CGFloat color[4];
}
@end

// MyObject.m

@implementation MyObject

-(id) init
{
    self = [super init];
    if (self != nil)
    {
        color[0] = red;
        color[1] = green;
        color[2] = blue;
        color[3] = alpha;
    }
    return self;
}

Upvotes: 2

Ukko
Ukko

Reputation: 2266

You are better off using a NSColor object if you can.

However, to your original question one of my first questions is where do you want to create this array. When you say put it in a header do you mean as a member of a class or as a global array, you certainly can do both however there are some serious gotchas with putting globals in headers. If you need that follow up and I can explain it better.

If it is in a class then you can just declare it like any other member field. If you say

CGFloat color[4];

then the space for the array is allocated in your object itself. You can also just use a 

CGFloat *color;

or its moral equivalent to refer to an array that is stored outside of the object. You do need to manage that storage appropriately however.

This matters in the case you hinted at where you use a constant array object and cannot later change it. That can happen but is rare, since it cannot happen with the first approach, you don't see it in the wild very often.

There is a whole dissertation on the corner cases in here, I am sure it is not helping to go into it. Just use CGFloat color[4] in your object and it won't matter, by the time you see things they will be mutable and you can just use them the way you expect.

Upvotes: 0

Donal Fellows
Donal Fellows

Reputation: 137567

You'd need to put the size in so that enough space is reserved.

CGFloat color[4];

Or use a pointer to the array, but that's more work and hardly superior for representing something as well-known as a color.

Upvotes: 0

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