- (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];