Ada：如何检查输入是否为枚举类型 [英] Ada: How to check if input is an enumeration type

问题描述

我正在从键盘上读取输入。输入应该与枚举类型中定义的元素之一匹配。这是枚举类型的示例：

I am reading input from the keyboard. The input is supposed to match one of the elements defined in an enumeration type. Here is an example of the enum type:

type NameType is (Bob, Jamie, Steve);

如果我收到的输入不是这3个中的一个，则ada引发IO异常。我如何处理此问题，使其仅显示重试消息而又不让程序停止？谢谢

If I receive an input that is not one of these 3, ada raises an IO exception. How do I handle this to where I can simply display a "try again" message and not have the program stop? THANKS

推荐答案

创建 Enumeration_IO for Name_Type ，例如说 Name_IO 。在 循环 ，输入一个嵌套的 block 处理出现的任何 Data_Error 。当 Name_IO.Get 成功时， 退出 循环。

Create an instance of Enumeration_IO for Name_Type, say Name_IO. In a loop, enter a nested block to handle any Data_Error that arises. When Name_IO.Get succeeds, exit the loop.

with Ada.IO_Exceptions;
with Ada.Text_IO;

procedure Ask is

type Name_Type is (Bob, Jamie, Steve);
package Name_IO is new Ada.Text_IO.Enumeration_IO (Name_Type);

begin
   loop
      declare
         Name : Name_Type;
      begin
         Ada.Text_IO.Put("Enter a name: ");
         Name_IO.Get(Name);
         exit;
      exception
         when Ada.IO_Exceptions.Data_Error =>
            Ada.Text_IO.Put_Line("Unrecognized name; try again.");
      end;
   end loop;
end Ask;

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