Fortran - 派生資料型別

Fortran 允許您定義派生資料型別。派生資料型別也稱為結構，它可以包含不同型別的資料物件。

派生資料型別用於表示記錄。例如，您想跟蹤圖書館中的書籍，您可能希望跟蹤以下關於每本書的屬性：

• 標題
• 作者
• 主題
• 圖書 ID

定義派生資料型別

要定義派生資料型別，使用 type 和end type語句。type 語句定義了一種新的資料型別，為您的程式提供了多個成員。type 語句的格式如下：

type type_name      
   declarations
end type 

以下是您宣告 Book 結構的方式：

type Books
   character(len = 50) :: title
   character(len = 50) :: author
   character(len = 150) :: subject
   integer :: book_id
end type Books

訪問結構成員

派生資料型別的物件稱為結構。

可以在型別宣告語句中建立 Books 型別的結構，例如：

type(Books) :: book1 

可以使用元件選擇符字元（%）訪問結構的元件：

book1%title = "C Programming"
book1%author = "Nuha Ali"
book1%subject = "C Programming Tutorial"
book1%book_id = 6495407

請注意，% 符號前後沒有空格。

示例

以下程式說明了上述概念：

program deriveDataType

   !type declaration
   type Books
      character(len = 50) :: title
      character(len = 50) :: author
      character(len = 150) :: subject
      integer :: book_id
   end type Books
   
   !declaring type variables
   type(Books) :: book1 
   type(Books) :: book2 
   
   !accessing the components of the structure
   
   book1%title = "C Programming"
   book1%author = "Nuha Ali"
   book1%subject = "C Programming Tutorial"
   book1%book_id = 6495407 
   
   book2%title = "Telecom Billing"
   book2%author = "Zara Ali"
   book2%subject = "Telecom Billing Tutorial"
   book2%book_id = 6495700
  
   !display book info
   
   Print *, book1%title 
   Print *, book1%author 
   Print *, book1%subject 
   Print *, book1%book_id  
   
   Print *, book2%title 
   Print *, book2%author 
   Print *, book2%subject 
   Print *, book2%book_id  

end program deriveDataType

當編譯並執行上述程式碼時，會產生以下結果：

 C Programming                                     
 Nuha Ali                                          
 C Programming Tutorial            
   6495407
 Telecom Billing                                   
 Zara Ali                                          
 Telecom Billing Tutorial            
   6495700

結構陣列

您還可以建立派生型別的陣列：

type(Books), dimension(2) :: list

可以按如下方式訪問陣列的各個元素：

list(1)%title = "C Programming"
list(1)%author = "Nuha Ali"
list(1)%subject = "C Programming Tutorial"
list(1)%book_id = 6495407

以下程式說明了該概念：

program deriveDataType

   !type declaration
   type Books
      character(len = 50) :: title
      character(len = 50) :: author
      character(len = 150) :: subject
      integer :: book_id
   end type Books
   
   !declaring array of books
   type(Books), dimension(2) :: list 
    
   !accessing the components of the structure
   
   list(1)%title = "C Programming"
   list(1)%author = "Nuha Ali"
   list(1)%subject = "C Programming Tutorial"
   list(1)%book_id = 6495407 
   
   list(2)%title = "Telecom Billing"
   list(2)%author = "Zara Ali"
   list(2)%subject = "Telecom Billing Tutorial"
   list(2)%book_id = 6495700
  
   !display book info
   
   Print *, list(1)%title 
   Print *, list(1)%author 
   Print *, list(1)%subject 
   Print *, list(1)%book_id  
   
   Print *, list(1)%title 
   Print *, list(2)%author 
   Print *, list(2)%subject 
   Print *, list(2)%book_id  

end program deriveDataType

當編譯並執行上述程式碼時，會產生以下結果：

C Programming                                     
Nuha Ali                                          
C Programming Tutorial               
   6495407
C Programming                                     
Zara Ali                                          
Telecom Billing Tutorial                                      
   6495700