Objective-c MRC multiple objects referencing each other in memory management

In the MRC environment, assuming that the Ctroom object is a member variable of Ctperson, it should be noted that the code is as follows when modifying the Ctroom object:

-(void) Setroom: (Ctroom *) room{
It is necessary to determine whether the new and old values are equal and, once equal, [_room release] is equivalent to [window release], then [retain] throws an exception.     if (_room! = ) {         [_room release];  Release old value         = [retain]; Retain new value    }}

-(void) Dealloc

{

[_room release];

_room = nil;

self. Bedroom = nil;//At the same time, this sentence code is equivalent to the previous two sentences

[Super Dealloc];]

}

    Ctperson *person = [[Ctperson alloc] init];     *r = [[Ctroom alloc] init];    [Person Setroom:r];    [R Release];     = R;    [Person release];    

Objective-c MRC multiple objects referencing each other in memory management