D 程式設計 - 結構體

結構體是D程式語言中另一種使用者自定義的資料型別，它允許您組合不同型別的資料項。

結構體用於表示記錄。假設您想跟蹤圖書館中書籍的資訊。您可能需要跟蹤每本書的以下屬性：

書名
作者
主題
圖書ID

定義結構體

要定義結構體，必須使用struct語句。struct語句定義了一種新的資料型別，該型別包含程式的多個成員。struct語句的格式如下：

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

結構體標籤是可選的，每個成員定義都是一個普通的變數定義，例如int i; 或float f; 或任何其他有效的變數定義。在結構體定義結束前的分號之前，您可以指定一個或多個結構體變數，這些變數是可選的。以下是宣告Books結構體的方法：

struct Books {
   char [] title;
   char [] author;
   char [] subject;
   int   book_id;
};

訪問結構體成員

要訪問結構體的任何成員，可以使用成員訪問運算子 (.)。成員訪問運算子表示為結構體變數名和我們希望訪問的結構體成員之間的句點。您將使用struct關鍵字定義結構體型別的變數。以下示例說明了結構體的用法：

線上演示

import std.stdio; 
 
struct Books { 
   char [] title; 
   char [] author; 
   char [] subject; 
   int   book_id; 
}; 
 
void main( ) { 
   Books Book1;        /* Declare Book1 of type Book */ 
   Books Book2;        /* Declare Book2 of type Book */ 
   
   /* book 1 specification */ 
   Book1.title = "D Programming".dup; 
   Book1.author = "Raj".dup; 
   Book1.subject = "D Programming Tutorial".dup;
   Book1.book_id = 6495407; 
   
   /* book 2 specification */ 
   Book2.title = "D Programming".dup; 
   Book2.author = "Raj".dup; 
   Book2.subject = "D Programming Tutorial".dup; 
   Book2.book_id = 6495700; 
   
   /* print Book1 info */ 
   writeln( "Book 1 title : ", Book1.title); 
   writeln( "Book 1 author : ", Book1.author); 
   writeln( "Book 1 subject : ", Book1.subject); 
   writeln( "Book 1 book_id : ", Book1.book_id);  
   
   /* print Book2 info */ 
   writeln( "Book 2 title : ", Book2.title); 
   writeln( "Book 2 author : ", Book2.author); 
   writeln( "Book 2 subject : ", Book2.subject); 
   writeln( "Book 2 book_id : ", Book2.book_id); 
}

編譯並執行上述程式碼後，將產生以下結果：

Book 1 title : D Programming 
Book 1 author : Raj 
Book 1 subject : D Programming Tutorial 
Book 1 book_id : 6495407 
Book 2 title : D Programming 
Book 2 author : Raj 
Book 2 subject : D Programming Tutorial 
Book 2 book_id : 6495700

結構體作為函式引數

您可以像傳遞任何其他變數或指標一樣，以非常類似的方式將結構體作為函式引數傳遞。您將以與上述示例中相同的方式訪問結構體變數：

線上演示

import std.stdio;

struct Books { 
   char [] title; 
   char [] author; 
   char [] subject; 
   int   book_id; 
}; 
 
void main( ) { 
   Books Book1;        /* Declare Book1 of type Book */ 
   Books Book2;        /* Declare Book2 of type Book */  
   
   /* book 1 specification */ 
   Book1.title = "D Programming".dup; 
   Book1.author = "Raj".dup; 
   Book1.subject = "D Programming Tutorial".dup; 
   Book1.book_id = 6495407;  
   
   /* book 2 specification */ 
   Book2.title = "D Programming".dup; 
   Book2.author = "Raj".dup; 
   Book2.subject = "D Programming Tutorial".dup; 
   Book2.book_id = 6495700;  
   
   /* print Book1 info */ 
   printBook( Book1 );  
   
   /* Print Book2 info */ 
   printBook( Book2 );  
}
 
void printBook( Books book ) { 
   writeln( "Book title : ", book.title); 
   writeln( "Book author : ", book.author); 
   writeln( "Book subject : ", book.subject); 
   writeln( "Book book_id : ", book.book_id); 
}

編譯並執行上述程式碼後，將產生以下結果：

Book title : D Programming 
Book author : Raj 
Book subject : D Programming Tutorial 
Book book_id : 6495407 
Book title : D Programming 
Book author : Raj
Book subject : D Programming Tutorial 
Book book_id : 6495700

結構體初始化

結構體可以透過兩種形式初始化，一種使用建構函式，另一種使用{}格式。以下顯示了一個示例。

示例

線上演示

import std.stdio;

struct Books { 
   char [] title; 
   char [] subject = "Empty".dup; 
   int   book_id = -1; 
   char [] author = "Raj".dup;  
}; 
 
void main( ) { 
   Books Book1 = Books("D Programming".dup, "D Programming Tutorial".dup, 6495407 ); 
   printBook( Book1 ); 
   
   Books Book2 = Books("D Programming".dup, 
      "D Programming Tutorial".dup, 6495407,"Raj".dup ); 
   printBook( Book2 );
   
   Books Book3 =  {title:"Obj C programming".dup, book_id : 1001};
   printBook( Book3 ); 
}
  
void printBook( Books book ) { 
   writeln( "Book title : ", book.title); 
   writeln( "Book author : ", book.author); 
   writeln( "Book subject : ", book.subject); 
   writeln( "Book book_id : ", book.book_id); 
}

編譯並執行上述程式碼後，將產生以下結果：

Book title : D Programming 
Book author : Raj 
Book subject : D Programming Tutorial 
Book book_id : 6495407 
Book title : D Programming 
Book author : Raj 
Book subject : D Programming Tutorial 
Book book_id : 6495407 
Book title : Obj C programming 
Book author : Raj 
Book subject : Empty 
Book book_id : 1001

靜態成員

靜態變數只初始化一次。例如，為了使圖書具有唯一的ID，我們可以將book_id設為靜態並遞增圖書ID。以下顯示了一個示例。

示例

線上演示

import std.stdio;  

struct Books { 
   char [] title; 
   char [] subject = "Empty".dup; 
   int   book_id; 
   char [] author = "Raj".dup; 
   static int id = 1000; 
}; 
 
void main( ) { 
   Books Book1 = Books("D Programming".dup, "D Programming Tutorial".dup,++Books.id ); 
   printBook( Book1 );  
   
   Books Book2 = Books("D Programming".dup, "D Programming Tutorial".dup,++Books.id); 
   printBook( Book2 );  
   
   Books Book3 =  {title:"Obj C programming".dup, book_id:++Books.id}; 
   printBook( Book3 ); 
}
  
void printBook( Books book ) { 
   writeln( "Book title : ", book.title); 
   writeln( "Book author : ", book.author); 
   writeln( "Book subject : ", book.subject); 
   writeln( "Book book_id : ", book.book_id); 
}

編譯並執行上述程式碼後，將產生以下結果：

Book title : D Programming 
Book author : Raj 
Book subject : D Programming Tutorial 
Book book_id : 1001 
Book title : D Programming 
Book author : Raj 
Book subject : D Programming Tutorial 
Book book_id : 1002 
Book title : Obj C programming 
Book author : Raj 
Book subject : Empty 
Book book_id : 1003

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