Question

When I compile with the following code there are no errors:

@class RootViewController;
//#import "RootViewController.h"

When I compile with the following code I get an error:

//@class RootViewController;
#import "RootViewController.h"

“error: expected specifier-qualifier-list before ‘RootViewController'”

I don’t understand what the difference is between the two because I used #import in a similar class and it compiled without errors!

Answer 1

I decided to refer to the documentation because I was still confused:

#import

This directive is identical to #include, except that it makes sure that the same file is never included more than once. It’s therefore preferred and is used in place of #include in code examples throughout Objective-C–based documentation.

This convention means that every interface file includes, indirectly, the interface files for all inherited classes. When a source module imports a class interface, it gets interfaces for the entire inheritance hierarchy that the class is built upon.

@class

Declarations like this simply use the class name as a type and don’t depend on any details of the class interface (its methods and instance variables), the @class directive gives the compiler sufficient forewarning of what to expect. However, where the interface to a class is actually used (instances created, messages sent), the class interface must be imported.

http://developer.apple.com/iphone/library/documentation/Cocoa/Conceptual/ObjectiveC/Articles/ocDefiningClasses.html#//apple_ref/doc/uid/TP30001163-CH12-TPXREF123