结构（Structs）

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2023-12-01

该structure是D编程中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。

结构用于表示记录。假设您想要在图书馆中跟踪您的图书。您可能希望跟踪每本书的以下属性 -

Title
Author
Subject
Book ID

定义一个结构 (Defining a Structure)

要定义结构，必须使用struct语句。 struct语句定义一个新的数据类型，为您的程序提供多个成员。 struct语句的格式是这样的 -

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

structure tag是可选的，每个成员定义是一个普通的变量定义，例如int i; 或浮动f; 或任何其他有效的变量定义。在分号前面的结构定义的末尾，您可以指定一个或多个可选的结构变量。以下是您声明图书结构的方式 -

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

访问结构成员 (Accessing Structure Members)

要访问结构的任何成员，请使用member access operator (.) 。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。以下示例说明了结构的用法 -

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); 
}

编译并执行上述代码时，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

作为函数参数的结构 (Structures as Function Arguments)

您可以将结构作为函数参数传递，与传递任何其他变量或指针的方式非常相似。您将以与上面示例中访问过的方式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 );  
   /* 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); 
}

编译并执行上述代码时，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

结构初始化

结构可以用两种形式初始化，一种使用construtor，另一种使用{}格式。一个例子如下所示。

例子 (Example)

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); 
}

编译并执行上述代码时，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

静态变量只初始化一次。例如，要获得书籍的唯一ID，我们可以将book_id设置为静态并增加书籍ID。一个例子如下所示。

例子 (Example)

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); 
}

编译并执行上述代码时，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