Question

Here is my code:

NSString *xyz=[NSString stringWithFormat:@"%i %@",10,@"Sagar"];

Now I am taking other string, as follows.

NSString *x2=[xyz copy];

I don’t know exactly what will happen here? Is it something like, x2 has the ref of xyz’s ref?

NSString *x3=[xyz retain];

What will happen here, x3 has a new memory having copied string or [xyz copy] does that?

Now, how to remove all these three strings from memory?

Answer 1

NSString *xyz=[NSString stringWithFormat:@"%i %@",10,@"Sagar"];

This will create autoreleased instance of NSString – it will be released when the autorelease pool is drained (typically on the next run loop).

NSString *x2 = [xyz copy];

In theory -copy message will create a new instance of the object with retain count 1 (that is you must release it somewhere), but as NSString object is immutable then [xyz copy] will be optimized to [xyz retain] and thus it will point to the same instance.

NSString *x3=[xyz retain];

x3 will point to the same instance as xyz (and x2), and its retain count will be incremented – you must release your object somewhere.

Now, how to remove all these three
strings from memory?

Make sure that you pair all retain (copy) messages with release and memory will be freed.
Read Objective-c memory management guide for more details.