With ARC , why the dealloc not called - objective-c

Question

I have enable the ARC. but this code makes me wonder
#interface Dog : NSObject
#end
#implementation Dog
- (void)dealloc
{
printf("Dog is dealloc\n"); //the function not called
}
#end
#interface Person : NSObject
#property (nonatomic, strong) Dog *dog;
#end
#implementation Person
- (void)dealloc
{
printf("Person is dealloc\n");
_dog = nil;
}
-(Dog *)dog
{
return _dog;
}
#end
int main()
{
Person *p = [[Person alloc] init];
p.dog = [[Dog alloc]init];
Dog* d = p.dog;
d=nil;
p=nil;
printf("end\n");
return 0;
}
the result is
Person is dealloc
end
Program ended with exit code: 0
why the dog's dealloc method not called.
and then I commented out this Method, the dog's dealloc method called.
//-(Dog *)dog
//{
// return _dog;
//}
thank you very much.

Answer 1

You can see the memory graph to find out what exactly points to the Dog and preserve it from automatically deallocation:
Unlike Swift, In Objective-C, you need to put the main body inside an #autoreleasepool to make it ARC compatible:
int main(int argc, const char * argv[]) {
#autoreleasepool {
// insert code here...
NSLog(#"Hello, World!");
Person *p = [[Person alloc] init];
p.dog = [[Dog alloc]init];
Dog* d = p.dog;
d = nil;
p = nil;
printf("Ended...\n");
}
return 0;
}
Then you will see this in the output:
Person is dealloc
Ended...
Dog is dealloc