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D 语言 - 结构

结构是 D 语言编程中可用的另一种用户定义的数据类型，它允许您组合不同类型的数据项。

结构体用于表示记录。 假设您想跟踪图书馆中的书籍。 您可能想要跟踪每本书的以下属性 −

  • Title
  • Author
  • Subject
  • Book ID

定义结构

要定义结构，必须使用 struct 语句。 struct 语句定义了一种新的数据类型，为您的程序提供了多个成员。 struct 语句的格式是这样的 −

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

结构体标签是可选的，每个成员定义都是普通的变量定义，如 int i； 或 float f； 或任何其他有效的变量定义。 在结构定义末尾的分号之前，您可以指定一个或多个可选的结构变量。 以下是声明 Books 结构的方法 −

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

访问结构成员

要访问结构体的任何成员，可以使用成员访问运算符 (.)。 成员访问运算符被编码为结构变量名称和我们希望访问的结构成员之间的句点。 您可以使用 struct 关键字来定义结构类型的变量。 下面的例子解释了结构体的用法 −

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); 
}

当上面的代码被编译并执行时，会产生以下结果 −

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

结构作为函数参数

您可以将结构作为函数参数传递，其方式与传递任何其他变量或指针非常相似。 您可以按照与上例中访问类似的方式访问结构变量 −

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 );  
   
   /* 打印 Book2 信息 */ 
   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); 
}

当上面的代码被编译并执行时，会产生以下结果 −

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

结构体初始化

结构体可以通过两种形式初始化，一种使用构造函数，另一种使用 {} 格式。 一个例子如下所示。

示例

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); 
}

当上面的代码被编译并执行时，会产生以下结果 −

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

静态成员

静态变量仅初始化一次。 例如，要获得书籍的唯一 id，我们可以将 book_id 设置为静态并递增书籍 id。 一个例子如下所示。

示例

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); 
}

当上面的代码被编译并执行时，会产生以下结果 −

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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