This is not a language level issue; it is a platform level packaging issue. In both Mac OS X and iOS, as a rule, you will add a resource file to your project, then get the file path with NSBundle:
NSString *path = [[NSBundle mainBundle] pathForResource:@"file" ofType:@"xml"];
Objective-C . , Mac OS X, mainBundle , , bundleForClass:.
iOS , , . .