What are the retain count of NSStrings allocations mentioned below - ios

Question

Here I allocated NSString variables ten different ways, and I want to know the retain count for all of them.
#interface SomeClass : NSObject
{
NSString *str1;
NSString *str2;
}
#property (nonatomic, retain) NSString* str1;
#property (nonatomic, copy) NSString * str2;
- str1 =#"hello";
- self.str1 = #"hello";
- str1 = [[NSString alloc]init];
- self.str4 = [[NSString alloc]init];
- str1 = [[[NSString alloc]init]autorelease];
- self.str1 = [[[NSString alloc]init]autorelease];
- str1 = [[NSString alloc]initWithString:#"hello"];
- self.str1 = [[NSString alloc]initWithString:#"hello"];
- str1 = [[[NSString alloc]initWithString:#"hello"]autorelease];
- self.str1 = [[[NSString alloc]initWithString:#"hello"]autorelease];
What are the retain count of NSString allocations mentioned above? How can I know the retain count of them are retain count different for all of them?

Answer 1

While this seems like a homework assignment, you can call retainCount on each string to get an approximation of the real value. You should absolutely not use this method for any logic in a production app (see http://whentouseretaincount.com)! The documentation states:
Special Considerations
This method is of no value in debugging memory management issues. Because any number of framework objects may have retained an object in order to hold references to it, while at the same time autorelease pools may be holding any number of deferred releases on an object, it is very unlikely that you can get useful information from this method.

Answer 2

I assume they are accessed in some SomeClass method. Variants:
// replace str1 with str2(copy), retain count will remain the same
str1 = #"hello";
self.str1 = #"hello"
str1 = [[NSString alloc]initWithString:#"hello"];
self.str1 = [[NSString alloc]initWithString:#"hello"];
str1 = [[[NSString alloc]initWithString:#"hello"]autorelease];
self.str1 = [[[NSString alloc]initWithString:#"hello"]autorelease];
Here you'll end up with a huge value, like UINT_MAX, compiler will optimize your code (you pass literal value, NSString is immutable) and those objects will be unreleasable.
self.str1 = [[NSString alloc] initWithFormat:#"a string %d", 5]; // with autorelease or not - the same
Here you'll end up with a release count = 2, you alloc string +1, you assign a retain property +1 = 2.
self.str2 = [[NSString alloc] initWithFormat:#"a string %d", 5]; // with autorelease or not - the same
Here you'll end up with a release count = 1, you alloc string +1, you assign a copy proprty, thus create a copy of created string = 1.
In all other situations you'll end up with release count = 1, autorelease does not add to retain count, it just decrements it by 1 when the pool drains.
Just remember:
Do not rely on retainCount,
When you create object via alloc, new, copy, mutable copy - it's your responsibility to release it. If you create object with like [NSString string] it will be autoreleased.
retain property retains object, copy property copies object, properties are usually used via dot notation (self.property etc.) (there's also set%Property% and %property% methods synthesized, so self.property = ... is (usually) the same as [self setProperty:...])
It's time to move to ARC. So if you can you should.