定義結構和訪問結構成員

Created: November-22, 2018

struct 語句的格式如下：

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

示例：宣告 ThreeFloats 結構：

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

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

使用引數 @threeFloats 傳送訊息 valueForKey：的 MyClass 例項將呼叫 MyClass 方法 threeFloats 並返回包含在 NSValue 中的結果。