Warning: (Insert object here) may not respond to '+alloc' ?

Question

I'm just getting started with Objective C development, and the following example that I am working with results in the following error:
fraction.m:6: warning: ‘Fraction’ may not respond to ‘+alloc’
fraction.m:6: warning: (Messages without a matching method signature
fraction.m:6: warning: will be assumed to return ‘id’ and accept
fraction.m:6: warning: ‘...’ as arguments.)
fraction.m:6: warning: no ‘-init’ method found
fraction.m:8: warning: ‘Fraction’ may not respond to ‘-free’
I am running Snow Leopard, and I have downloaded the most recent XCode and iPhone dev libraries.
I would very much appreciate your input. Thank you.
==========
#import <stdio.h>
#import <objc/Object.h>
/* Interface */
@interface Fraction: Object
int numerator;
int denominator;
-(void) print;
-(void) setNumerator: (int) n;
-(void) setDenominator: (int) d;
-(int) numerator;
-(int) denominator;
@end
/* Implementation */
@implementation Fraction;
-(void) print
printf ("%i,%i", numerator, denominator);
-(void) setNumerator: (int) n {
numerator = n;
-(void) setDenominator: (int) d {
denominator = d;
-(int) numerator {
return numerator;
-(int) denominator {
return denominator;
@end
int main (int argc, char *argv[])
Fraction* myFraction = [[Fraction alloc] init];
[myFraction free];
return 0;
}

Answer 1

tkambler wrote:
I've determined that this script compiles just fine on my iMac running 10.5.8. My other iMac, which I just installed Snow Leopard on, is the one that is giving me the errors. Any thoughts?
Fraction.m compiled and ran under Xcode without any problems on my OS X 10.5.5 system. I don't have a Snow Leopard system, so can't reproduce the errors you reported.
My first guess would be that the difference in your two systems is a difference in the included Object.h file. On my system the included file lives in /Developer/SDKs/MacOSX10.5.sdk/usr/include/objc. That @interface does indeed declare alloc, init, free, etc.
From the compiler warnings you posted (which don't include "Can't find Object.h"), I would assume that either the Object.h file at the above path has changed, or that the wrong Object.h file is being included. The latter needs to be ruled out because (at least on my system) there are several Object.h files intended for different purposes. So for example, if your Snow Leopard Xcode isn't searching in the same folders, or if the correct Object.h has been relocated, it's entirely possible the wrong file is being included during the build.
Determining which possibility applies in your case may require some familiarity with OS X and Xcode, and I don't know if +just getting started with Objective C+ means just that, or whether OS X and all of the developer tools are also new for you. If the code you posted is part of an isolated exercise and you won't be using Object.h much in the future (since it's not used in Cocoa), my advice would be to stay on the system that works until you're done with the current exercise.
If you have a requirement to program in Obj-C without using Cocoa for an extended period of time, I'm sure someone here can help you find out what happened to Object.h on your Snow Leopard system. Of course things will be a lot easier if that help comes from someone who already has Snow Leopard.
You can get started by looking at the Object.h file Xcode is including. You can do this by selecting Object.h in a text editor window, then selecting File->Open Quickly from the top menu (see Opening Files by Filename or Symbol Name in the Xcode Workspace Guide). Is your Active SDK set to 10.6? If your Snow Leopard Xcode has the option to set the Active SDK to 10.5, see which Object.h file gets included in that case.
Hope that helps!
\- Ray