定义结构和访问结构成员

Created: November-22, 2018

struct 语句的格式如下：

struct [structure tag]
{
   member definition;
   member definition;
   ...
   member definition;
} [one or more structure variables];

示例：声明 ThreeFloats 结构：

   typedef struct {
    float x, y, z;
} ThreeFloats;

@interface MyClass
- (void)setThreeFloats:(ThreeFloats)threeFloats;
- (ThreeFloats)threeFloats;
@end

使用参数 @threeFloats 发送消息 valueForKey：的 MyClass 实例将调用 MyClass 方法 threeFloats 并返回包含在 NSValue 中的结果。