Person *p = [[Person alloc] init]; // P 1
    NSUInteger c = [p retainCount];
    NSLog(@"计数器：%ld",c);
    [p retain];     //p 2
     c = [p retainCount];
    NSLog(@"计数器：%ld",c);
    [p release]; //p 1
    c = [p retainCount];
    NSLog(@"计数器：%ld",c);
    [p release];  //野指针 这里p的引用应该为0 才是，但是还是1，必须将p =nil,这时 p retainCount的值才是0
    c = [p retainCount];
    NSLog(@"计数器：%ld,%p",c,p);
    //p.age = 10;对象已经被释放，将出现内存错误

Person *p = [[Person alloc] init]; // P 1
    NSUInteger c = [p retainCount];
    NSLog(@"计数器：%ld",c);
    [p retain];     //p 2
     c = [p retainCount];
    NSLog(@"计数器：%ld",c);
    [p release]; //p 1
    c = [p retainCount];
    NSLog(@"计数器：%ld",c);
    [p release];  //野指针 这里p的引用应该为0 才是，但是还是1，必须将p =nil,这时 p retainCount的值才是0
    c = [p retainCount];
    NSLog(@"计数器：%ld,%p",c,p);
    //p.age = 10;对象已经被释放，将出现内存错误