Question

As far as I know, NSString is “created once and readonly” type. When reassigning value to a NSString, we in fact change the pointer’s value making it point to another memory address, but the NSString object remains unchanged.

My question is: if the NSString object has no other pointers pointing to it, is that causing a memory leak after reassigning?

To discuss in details, please read the following code:

@interface ViewController ()
@property (nonatomic,strong) NSString* aString;
@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.aString = [NSString stringWithFormat:@"Hello %@",@"Philip"];

    // only for setting a break point
    int x;

    // reassigning 
    self.aString = [NSString stringWithFormat:@"Goodbye"];

    // only for setting another break point
    int y;
}

@end

In debug console:

(lldb) po self.aString
(NSString *) $0 = 0x00337d00 Hello Philip
(lldb) po self.aString
(NSString *) $1 = 0x3f41dfe0 Goodbye
(lldb) 

It clearly shows that after reassigning value, aString now points to a different memory location. My another question is: how can I display the object that starts at 0x00337d00 in debug console?

Answer 1

If the NSString has no pointer to it, it should get dealloc’ed. That may only happen after the autorelease pool is drained thought, since it was created with a method that should return it autoreleased.

Also literal NSStrings like @"string" never get dealloc’ed, since they are actually constants (somewhat like singletons).