Question

I am somewhat confused about memory allocation of static variable in objective C.

1. should we allocate memory for static variable using alloc:? and
   initialize it usinginit:?

2. Is objective c static variable same as c static variable?

3. is it worth to apply retain on static variable?

Answer 1

There are a couple of things you need to take into account.

First, static C-like variables inside functions are technically fine. This should be:

- (void) f
{
    static NSString* s = nil;
    if (s == nil) {
        s = [[NSString alloc] initWithString:@"Hello"];
    }
}

The problem is that you will probably never be able to release, since s scope is only f function.

This is exactly like a C static variable inside a function.

There is also static usage to control visibility of a variable in a translation unit. So, if you want to only allow some variable to be accessed within file.c, just like C, you need to write in that file:

static NSString *s = [[NSString alloc] initWithString:@"Hello"];

Again, unless you write a specific method to release when you application ends, it will probably leak memory.

Finally, you can have “object oriented like” static behavior. You don’t use static keyword here but as most object oriented languages, you can have class variables (in Java, C#, C++ and others, class variables are accomplished with the static keyword).