Question

I’m new in Objective-C and so I’ve some problem to understand the memory management. I create a project without ARC (to understand the memory management), and I would like to know how to avoid memory leaks.

I explain with some C++ code. For example, I want to create one matrix with 3 vectors so in C++ we can do (first method):

Matrix mat(Vector(1, 1, 1), Vector(2, 2, 2));

At the end of the function all objects are destroyed and there’re no memory leaks

In Objective-C we do something like that :

Matrix mat = [[Matrix alloc] init:[[Vector alloc] init:1:1:1]:[[Vector alloc] init:2:2:2]];

Which in C++ is (second method):

Matrix mat = new Matrix(new Vector(1, 1, 1), new Vector(2, 2, 2));

But by this way, we can’t destroy the 2 vectors and so we create memory leaks.

So my question is, is there a way to do the first method in Objective-C ? And if not, I think I have to create 2 temporary variables, which contain the 2 vectors and release after the initialization of the matrix or there’s another method to do that ?

Answer 1

You’re correct that you would need to use temporary variables to correctly release the objects.

Normally in pre-ARC code, you’d use autorelease instead:

Matrix mat = [[Matrix alloc] init:[[[Vector alloc] init:1:1:1] autorelease] :[[[Vector alloc] init:2:2:2] autorelease]];

Or, even better, you’d add a convenience method to Vector:

+ (Vector*) vector:(int)a :(int)b :(int)c
{
    return [[[Vector alloc] init:a :b :c] autorelease];
}

then use it:

Matrix mat = [[Matrix alloc] init:[Vector vector:1 :1 :1] :[Vector vector:2 :2 :2]];

(By the way, it’s bad form to name your methods without words before the colons — it’s difficult to read.)