How to do a natural sort on an NSArray?

NSStrings can be compared using the NSNumericSearch compare option.

One version:

NSInteger sort(Obj* a, Obj* b, void*) {
    return [[a title] compare:[b title] options:NSNumericSearch];
}

result = [array sortedArrayUsingFunction:&sort context:nil];

Or a bit more generic:

NSInteger sort(id a, id b, void* p) {
    return [[a valueForKey:(NSString*)p] 
            compare:[b valueForKey:(NSString*)p]
            options:NSNumericSearch];
}

result = [array sortedArrayUsingFunction:&sort context:@"title"]

Or using blocks:

result = [array sortedArrayUsingComparator:^(Obj* a, Obj* b) { 
    return [[a title] compare:[b title] options:NSNumericSearch]; 
}];

Those attempting to replicate the Finder's sorting behavior on Mac OS X 10.6 and later and iOS 4 and later can use localizedStandardCompare: as the comparator selector.

Those with the same goal on earlier versions of Mac OS X and/or iOS should use the solution described in the String Programming Guide.