Passing Object to Unallocated Pointer

Question

Let's say that I have declared an NSString like this

NSString *myString = [[NSString alloc] initWithString:@"Never Heard"];
NSString *tempString;

tempString = myString;

[myString release];

My question is why does it work? As you can see, I didn't alloc for the tempString. Therefore I don't think there is a need to release it. But if I try to alloc and init the tempString, it will bring an error.

NSString *myString = [[NSString alloc] initWithString:@"Never Heard"];
NSString *tempString = [[NSString alloc] init];

tempString = myString;

[myString release];

I use NSString as example, but instead I have different classes implemented. I'm trying to emphasize how memory allocation works here. Care to clarify and explain?

Answer 1

A pointer is simply a memory address. You only create one object, and then you point tempString to that object. And tempString == myString.

[myString release] deallocates the string, leaving both pointers pointing at deallocated memory.

Do no confuse variables with objects. Variables are simply are handles that you use to access objects. Creating a new variable does not mean you are creating a new object.

Answer 2

This is absolutely not about memory allocation. This is all about how pointers work. When you do this:

tempString = myString;

tempString points to the same object as myString. So calling any method on tempString is the same as calling them on myString.