Question

I am trying to learn objective c on windows. My program compiles with warnings

My code is

#include <objc/Object.h>

@interface Greeter:Object
{
  /* This is left empty on purpose:
   ** Normally instance variables would be declared here,
   ** but these are not used in our example.
   */
}

- (void)greet;

@end

#include <stdio.h>

@implementation Greeter

- (void)greet
{
    printf("Hello, World!\n");
}

@end

#include <stdlib.h>

int main(void)
{
    id myGreeter;
    myGreeter=[[Greeter alloc] init];
    [myGreeter greet];
    [myGreeter release];
    return EXIT_SUCCESS;
}

I compile my program on GNUStep using the following command

 gcc -o Greeter Greeter.m -I /GNUstep/System/Library/Headers -L /GNUstep/System/Libra
 /Libraries -lobjc -lgnustep-base -fconstant-string-class=NSConstantString

I get the following warnings on compilation

: 'Greeter' may not respond to '+alloc' [enabled by default]
: (Messages without a matching method signature [enabled by default]
: will be assumed to return 'id' and accept [enabled by default]
: '...' as arguments.) [enabled by default]
: no '-init' method found [enabled by default]
: no '-release' method found [enabled by default]

And so when I run my executable the object does not get instantiated.

I am using gcc from MinGW where gcc version is 4.6.2

–UPDATE—

The program runs fine when I extend from NSObject instead of Object

–UPDATE 2 —-

My Object.h looks like

#include <objc/runtime.h>

@interface Object
{
    Class isa;
}
@end

–UPDATE 3 —-

I have modified my code as follows. It compiles fine, but I am not sure if this is the right way to go about things

@interface Greeter
{
  /* This is left empty on purpose:
   ** Normally instance variables would be declared here,
   ** but these are not used in our example.
   */
}

- (void)greet;

+ (id)alloc;
- (id)init;
- release;

@end

#include <stdio.h>

@implementation Greeter

- (void)greet
{
    printf("Hello, World!\n");
}

+ (id)alloc
  {
    printf("Object created");
    return self;
  }

- (id)init
  {
    printf("Object instantiated");
    return self;
  }

- release {}

@end

#include <stdlib.h>

int main(void)
{
    id myGreeter;
    myGreeter=[[Greeter alloc] init];
    [myGreeter greet];
    [myGreeter release];
    return EXIT_SUCCESS;
}

Answer 1

From memory, the Object class does not implement retain counts, so it wouldn’t have release, it’ll have free or some other method. It should have +alloc and -init though. Since there’s no “Objective-C standard”, you’ll have to open up your objc/Object.h and see exactly what it offers.

Note that on GCC 4.6.2, objc/Object.h actually includes objc/deprecated/Object.h, meaning support for Object as a class may be fairly limited. If it doesn’t include it, try including it yourself:

#import <objc/deprecated/Object.h>