Question

About a year ago, when I first got into programming, I learned the hard way that variables don’t escape the scope of the condition they’re created in. For example:

-(void)someMethod {
    if (x == y) {
        NSString *string = [[NSString alloc] initWithString:@"Foo"];
        NSLog(string); // outputs "Foo" to console successfully
    }
    ...
    NSLog(string); // Doesn't work, we're out of the scope of the "if" statement.
}

My question is, is there any way to dynamically create variables within a conditional statement and be able to access them at other times, kind of like if I declared it in my @interface?

EDIT I guess I didn’t explain it well, I meant if I wanted to use it later in other methods.

Answer 1

You just need to declare (and optionally initialize) the variable outside of the if. So something like:

-(void)someMethod {

    NSString *string = nil;
    if (x == y) {
        string = [[NSString alloc] initWithString:@"Foo"];
        NSLog(string); // outputs "Foo" to console successfully
    }
    ...
    NSLog(string); 
}

EDIT

To respond to your clarification, ‘string’ here is a local variable, local to this method. You have other options like instance variables for example. Instance methods like this one (ones that start with ‘-‘) will have access to this instance’s (this object’s) instance variables.

So you could do:

@interface MyClass : NSObject {

    NSString *string; // <<-- This is an instance variable (aka "ivar")
}

- (void)someMethod;
- (void)someOtherMethod;
@end

@implementation MyClass

- (void)someMethod {

    string = @"Foo";
}

- (void)someOtherMethod {

    NSLog (string); 
   // will print "Foo" provided someMethod was called before this method
}


@end

Obviously there’s more to this than you can get in a short answer. You can have global variables. If you’re new to the language, you should read properties as a very useful tool for encapsulating instance variables (useful when you want to get the memory mgmt right). But hopefully that gets you pointed in the right direction at least.