Objective-C struct/結(jié)構(gòu)

Objective-C 數(shù)組允許您定義的變量的類型，可容納幾個(gè)數(shù)據(jù)項(xiàng)的同類，但結(jié)構(gòu)是另一個(gè)用戶定義的數(shù)據(jù)類型，它允許將不同種類的數(shù)據(jù)項(xiàng)在Objective-C編程。

結(jié)構(gòu)被用來代表一個(gè)記錄，假設(shè)想跟蹤書籍在圖書館?？赡芤櫽嘘P(guān)每本書的下列屬性：

• 標(biāo)題

• 作者

• 主題

• 圖書 ID

定義一個(gè)結(jié)構(gòu)

要定義一個(gè)結(jié)構(gòu)，必須使用結(jié)構(gòu)語句。結(jié)構(gòu)語句定義了一個(gè)新的數(shù)據(jù)類型，與一個(gè)以上的成員為程序。結(jié)構(gòu)語句的格式是這樣的：

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

結(jié)構(gòu)變量是可選的，每個(gè)成員的定義是一個(gè)正常的變量定義，如int;或float f;或任何其他有效的變量定義。結(jié)構(gòu)的定義在結(jié)束之前，最后是分號(hào)，可以指定一個(gè)或多個(gè)結(jié)構(gòu)變量，但它是可選的。這里有一種方法，可能聲明書的結(jié)構(gòu)：

struct Books
{
   NSString *title;
   NSString *author;
   NSString *subject;
   int   book_id;
} book;  

訪問結(jié)構(gòu)成員

要訪問任何成員的結(jié)構(gòu)，我們使用成員訪問運(yùn)算符（.）。成員訪問運(yùn)算符被編碼為一個(gè)結(jié)構(gòu)變量的名稱和結(jié)構(gòu)成員。使用struct關(guān)鍵字定義結(jié)構(gòu)類型的變量。下面的例子來解釋使用結(jié)構(gòu)：

#import <Foundation/Foundation.h>

struct Books
{
   NSString *title;
   NSString *author;
   NSString *subject;
   int   book_id;
};
 
int main( )
{
   struct Books Book1;        /* Declare Book1 of type Book */
   struct Books Book2;        /* Declare Book2 of type Book */
 
   /* book 1 specification */
   Book1.title = @"Objective-C Programming";
   Book1.author = @"Nuha Ali"; 
   Book1.subject = @"Objective-C Programming Tutorial";
   Book1.book_id = 6495407;

   /* book 2 specification */
   Book2.title = @"Telecom Billing";
   Book2.author = @"Zara Ali";
   Book2.subject = @"Telecom Billing Tutorial";
   Book2.book_id = 6495700;
 
   /* print Book1 info */
   NSLog(@"Book 1 title : %@
", Book1.title);
   NSLog(@"Book 1 author : %@
", Book1.author);
   NSLog(@"Book 1 subject : %@
", Book1.subject);
   NSLog(@"Book 1 book_id : %d
", Book1.book_id);

   /* print Book2 info */
   NSLog(@"Book 2 title : %@
", Book2.title);
   NSLog(@"Book 2 author : %@
", Book2.author);
   NSLog(@"Book 2 subject : %@
", Book2.subject);
   NSLog(@"Book 2 book_id : %d
", Book2.book_id);

   return 0;
}

上面的代碼編譯和執(zhí)行時(shí)，它會(huì)產(chǎn)生以下結(jié)果：

2013-09-14 04:20:07.947 demo[20591] Book 1 title : Objective-C Programming
2013-09-14 04:20:07.947 demo[20591] Book 1 author : Nuha Ali
2013-09-14 04:20:07.947 demo[20591] Book 1 subject : Objective-C Programming Tutorial
2013-09-14 04:20:07.947 demo[20591] Book 1 book_id : 6495407
2013-09-14 04:20:07.947 demo[20591] Book 2 title : Telecom Billing
2013-09-14 04:20:07.947 demo[20591] Book 2 author : Zara Ali
2013-09-14 04:20:07.947 demo[20591] Book 2 subject : Telecom Billing Tutorial
2013-09-14 04:20:07.947 demo[20591] Book 2 book_id : 6495700

作為函數(shù)參數(shù)的結(jié)構(gòu)

可以傳遞一個(gè)結(jié)構(gòu)非常相似的方式作為函數(shù)參數(shù)傳遞任何其他變量或指針。會(huì)以類似的方式訪問結(jié)構(gòu)變量，因?yàn)橐呀?jīng)在上面的例子訪問：

#import <Foundation/Foundation.h>

struct Books
{
   NSString *title;
   NSString *author;
   NSString *subject;
   int   book_id;
};

@interface SampleClass:NSObject

/* function declaration */
- (void) printBook:( struct Books) book ;

@end

@implementation SampleClass 

- (void) printBook:( struct Books) book
{
   NSLog(@"Book title : %@
", book.title);
   NSLog(@"Book author : %@
", book.author);
   NSLog(@"Book subject : %@
", book.subject);
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