Ada：打开不存在的文件时抛出错误的异常 [英] Ada: throwing wrong exception when opening a non-existent file

问题描述

这是此[post]的后续内容 Ada：读取文件时在单独的过程中添加异常

This is a follow up of this [post] Ada: Adding an exception in a separate procedure when reading a file

下面的代码打开了一个不存在的文件时，而不是抛出 ADA.IO_EXCEPTIONS.NAME_ERROR ，而是抛出 ADA.IO_EXCEPTIONS.STATUS_ERROR 。

When my code below opens a file that doesn't exist, instead of throwing a ADA.IO_EXCEPTIONS.NAME_ERROR, it is throwing a ADA.IO_EXCEPTIONS.STATUS_ERROR.

下面是代码。

主文件： test_read.adb ：

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Long_Float_Text_IO;
with Ada.Float_Text_IO;


procedure Test_Read is

   Input_File    : File_Type;
   value         : Long_Float;

   procedure Open_Data (File : in out  Ada.Text_IO.File_Type; Name : in String) is separate;

begin

   Open_Data (File => Input_File, Name => "fx.txt");

   while not End_Of_File (Input_File) loop
      Ada.Long_Float_Text_IO.Get (File => Input_File, Item => value);
      Ada.Long_Float_Text_IO.Put (Item => value, Fore => 3, Aft  => 5, Exp  => 0);
   Ada.Text_IO.New_Line;
   end loop;
    Ada.Text_IO.Close (File => Input_File);

end Test_Read;

而分开的过程主体 test_read-open_data.adb ：

separate (test_read)

procedure Open_Data (File : in out  Ada.Text_IO.File_Type;
                 Name : in String) is

   --this procedure prepares a file for reading
   begin
      begin
         Ada.Text_IO.Open
           (File => File,
            Mode => Ada.Text_IO.In_File,
            Name => Name);
      exception
         when Ada.Text_IO.Name_Error =>
         Ada.Text_IO.Put(File => Standard_Error, Item => "****File not found....****");
   end;
end Open_Data;

抛出的错误消息：

****File not found....****

Execution terminated by unhandled exception
Exception name: ADA.IO_EXCEPTIONS.STATUS_ERROR
Message: file not open
Call stack traceback locations:
0x40bf0f 0x40ead0 0x424b08 0x424e4a 0x4010b4 0x401146 0x7c817075
[2012-03-21 13:45:44] process exited with status 1 (elapsed time: 00.13s)

我尝试了一些操作：

1. 使用Ada.IO_Exceptions放入； 在 test_read.adb 并在Ada.IO_Exceptions.Name_Error => 时放置，而不是Ada.Text_IO.Name_Error = 时放置> 在 test_read-open_data.adb 中。但是没有变化。

1. Put with Ada.IO_Exceptions; in test_read.adb and put when Ada.IO_Exceptions.Name_Error => instead of when Ada.Text_IO.Name_Error => in test_read-open_data.adb. But there is no change.

在 test_read-open_data.adb 中，我更改了 Mode => Ada.Text_IO.In_File 使其变为 Mode => Ada.Text_IO.Out_File 如下所示：

In test_read-open_data.adb, I changed the line Mode => Ada.Text_IO.In_File to make it become Mode => Ada.Text_IO.Out_File as shown below:

Ada.Text_IO.Open
（文件=>文件，
模式=> Ada.Text_IO.Out_File，
名称=>名称）;

Ada.Text_IO.Open (File => File, Mode => Ada.Text_IO.Out_File, Name => Name);

但是没有改善。

那么如何获得正确 ADA.IO_EXCEPTIONS.NAME_ERROR ？

一个相关问题：

有什么区别Ada.Text_IO.Name_Error 和 ADA.IO_EXCEPTIONS.NAME_ERROR ？在我的程序中，当名称为 fx.txt 的文件不存在时，我想得到通知。这两个例外中的哪一个是适当的？

What's the difference between Ada.Text_IO.Name_Error and ADA.IO_EXCEPTIONS.NAME_ERROR? In my program I want to be informed when the file of name fx.txt does not exist. Which one of these two exceptions is appropriate?

非常感谢

更新（最新代码）

这是我更新的代码：

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Long_Float_Text_IO;
with Ada.Float_Text_IO;


procedure Test_Read is

   Input_File    : File_Type;
   value         : Long_Float;
   Success       : Boolean;

procedure Open_Data (File : in out  Ada.Text_IO.File_Type; Name : in String; Success : out Boolean) is separate;

begin

   Open_Data (File => Input_File, Name => "fx.txt", Success => Success);
   if not Success then
      return;
   end if;

   while not End_Of_File (Input_File) loop
      Ada.Long_Float_Text_IO.Get (File => Input_File, Item => value);
      Ada.Long_Float_Text_IO.Put (Item => value, Fore => 3, Aft  => 5, Exp  => 0);
      Ada.Text_IO.New_Line;
   end loop;
   Ada.Text_IO.Close (File => Input_File);
   Ada.Text_IO.Put_Line (Item => "Reading file success: " & Boolean'Image (Success));

end Test_Read;

和单独过程：

separate (test_read)

procedure Open_Data (File : in out  Ada.Text_IO.File_Type;
                 Name : in String; Success : out Boolean) is

   --this procedure prepares a file for reading
     begin
      Success := True;
      begin
         Ada.Text_IO.Open
           (File => File,
            Mode => Ada.Text_IO.Out_File,
            Name => Name);
      exception
         when Ada.Text_IO.Name_Error  =>
         Success := False;   
         Ada.Text_IO.Put (File => Standard_Error, Item => "****File not found....****");
      end;
end Open_Data;

在编译存在文件fx.txt 时，我得到：

On compiling with file fx.txt present, I get:

Execution terminated by unhandled exception
Exception name: ADA.IO_EXCEPTIONS.MODE_ERROR
Message: file not readable
Call stack traceback locations:
0x40bf2b 0x40ead0 0x424b58 0x424f5a 0x4010b4 0x401146 0x7c817075
[2012-03-22 08:39:39] process exited with status 1 (elapsed time: 00.14s)

文件内容 fx.txt **被删除，并且其内容在运行程序时不会显示**

And the contents of the file fx.txt **get erased and its contents are not displayed on running the program**

在编译并将文件fx.txt重命名为fy.txt时，我得到：

****File not found....****
[2012-03-22 08:45:31] process terminated successfully (elapsed time: 00.13s)

那出了什么问题？

推荐答案

输出正是我所期望的：a Name_Error 抛出并捕获，打印找不到文件，然后程序继续。 Open_Data 不会告诉调用者该文件尚未打开，并且对该文件的后续操作会触发 Status_Error 。例如，您可以在 Open_Data 的参数中添加 Success：out布尔值，或引发异常（一个您自己的，或者只是重新引发 Name_Error 。

The output is just what I would expect: a Name_Error is thrown and caught, File not found is printed, and the program continues. Open_Data does not tell its caller that the file has not been opened, and the subsequent operations on the file trigger a Status_Error. You could, for example, add a Success : out Boolean to Open_Data's parameters, or raise an exception (one of your own, or simply re-raise Name_Error.

例如

Open_Data (File => Input_File, Name => "fx.txt", Success => Success);
if not Success then
   return;
end if;

while not End_Of_File (Input_File) loop

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