oc __weak和__strong的区别

 id __weak obj=[[NSObject alloc]init];
    NSLog(@"弱引用自身地址:%p",&obj);
    NSLog(@"弱引用指向地址:%p",obj);

    id __strong obj0=[[NSObject alloc]init];
    id __weak obj1=obj0;
    NSLog(@"强引用自身地址:%p",&obj0);
    NSLog(@"弱引用自身地址:%p",&obj1);
    NSLog(@"强引用指向地址:%p",obj0);
    NSLog(@"弱引用指向地址:%p",obj1);
   
    obj1=nil;
//    obj0=nil;
    NSLog(@"弱引用销毁时强类型变量指向地址:%p",obj0);
    NSLog(@"弱引用销毁时弱类型变量指向地址:%p",obj1);