Question

Assume I have a interface like:

@interface it:NSObject
{
  NSString* string;
}
@end

@implement it
-(id)init
{
  if(self = [super init]){
    self.string = [[NSString alloc]init];
  }
}

-(void)dealloc
{
   [self.string release];
   [super release];
}
@end

If I use this class in another file and I call this:

it ait = [[it allow] init];
NSString* anotherString = [[NSString alloc] init];
ait.string = anotherString;
[anotherString release];

Will this cause the string alloced in init method of it a memory leak?
Since the string is not referenced and not autoreleased.
If I don’t alloc a string in the init method, what will happen when I call ait.string right before assign anotherString to it?

Answer 1

I think you need

@property (nonatomic, retain) NSString *string;

in your interface and

@synthesize string;

in your implementation for self.string to work.

Then, when you do

self.string = [[NSString alloc] init];

in your init method the string will actually have a retain count of 2 because [[NSString alloc] init]will return a string with a retain count of 1, and using self.string = will retain the object again because the property is declared as ‘retain’. This will result in a memory leak, but you can fix by having:

-(id)init
{
  if(self = [super init]){
    self.string = @"initString";
  }
}

or similar.

Then, onto the actual question, if you do as above the string allocated in init wont leak when you reassign with self.string = because properties marked as ‘retain’ release their current object before retaining the new one.

If you don’t assign a string to self.string in the init method it doesn’t matter because self.string will just return nil, which you can then deal with in your program.