Objective-C语言空消息未打印
示例
当NSLog要求打印空字符串时，它将完全省略日志。
NSString *name = @""; NSLog(@"%@", name); // Resolves to @""
上面的代码将不会打印任何内容。
为日志添加标签是一个好习惯：
NSString *name = @""; NSLog(@"Name: %@", name); // Resolves to @"Name: "
上面的代码将打印：
2016-07-21 14:20:28.623 App[87711:6153103] Name: