Objective-C MRC多个对象相互引用的内存管理

- (void) setRoom:(CTRoom *) room
{
　　 //需判断新旧值是否相等，一旦相等则[_room release]等价于[room release]，那么［room retain］将抛出异常。
    if(_room != room){ 
        [_room release];  //释放旧值
        _room = [room retain];　　//retain新值
    }
}

- (void) dealloc

{

//    [_room release];

//    _room = nil;

    self.room = nil; //同时,这一句代码等效前面两句

    [super dealloc];]

}

    CTPerson *person = [[CTPerson alloc] init];
    CTRoom *r = [[CTRoom alloc] init];
    [person setRoom:r];
    [r release];
    person.room = r;
    [person release];