Question

This is probably a question that is more about object alloc/retain/release, but I’ll use NSString as an example. I’m aware that I can do:

NSString* myString = [[NSString alloc] initWithString:@"Test"];

to essentially allocate and initialize a string referenced by my variable myString which I should later call [myString release] upon. However, if after I do this, I set it to some other string such as:

myString = someOtherString;

does that essentially create a memory leak because I’ve reassigned my pointer to another object and lost all reference to the original one I allocated?

If I simply want to personally allocate and release a string and then change its value at various times, should I be using a different syntax other than ‘=’ or is that overloaded to properly change the contents of the object that is originally represented by myString when I use =.

Answer 1

Yes, in your example you are leaking the memory.

NSString* myString = [[NSString alloc] initWithString:@"Test"];
myString = someOtherString;

You this should be done like so:

NSString* myString = [[NSString alloc] initWithString:@"Test"];
[myString release];
myString = someOtherString;

The best way I have heard the whole retain/release thing described is imagine you are walking a dog for someone. Your “object” is a dog and “retain” puts a leash on the dog and “release” takes a leash off. You can have as many leashes on the dog as you want but you want to keep at least one leash on the dog so he doesn’t run free (leak) and you want to take all the leashes off the dog once you get it back to the owner (you want to get rid of the object). In your example, you can think of it as letting go of the leash on the dog mid-walk and picking up the leash of a different dog.