在Ada中打开，写入和追加的过程 [英] Procedure to open, write and append in Ada

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问题描述

这个问题是后续的帖子在

关于在Ada中写入文件

我选择将这个问题放在一个单独的帖子中，以便更多人可以看到这个问题，因为我已经接受了一个稍有不同的问题（这是文件处理中的例外情况）。

  WITH Ada.Sequential_IO; 
与Ada.Float_Text_IO; 
 
 PROCEDURE TEST是
 
包Seq_Float_IO是新的Ada.Sequential_IO（Element_Type => Float）; 
 X_File：Seq_Float_IO.File_Type; 
 File_Name：String; 
 
 
过程Open_Data（File：in out Seq_Float_IO.File_Type; 
 Name：in String）是
 
 BEGIN 
 
开始
 Seq_Float_IO.Open（
 File =>文件，
 Mode => Seq_Float_IO.Append_File，
 Name => File_Name）; 
例外
当Seq_Float_IO.Name_Error => 
 Seq_Float_IO.Create（
 File => File，
 Mode => Seq_Float_IO.Out_File，
 Name => File_Name）; 
 end; 
 
 END Open_Data; 
 
 
 x：CONSTANT Float：= 2.0; 
 
 
 BEGIN  - 主程序
 Open_Data（X_File，xvalues.dat）; 
 Seq_Float_IO.Write（File => X_File，Item => x）; 
 
 Seq_Float_IO.Close（File => X_File）; 
结束测试;

在编译上面的代码时，我得到如下错误：

X_File：Seq_Float_IO.File_Type;
1. File_Name：String;
  |
  $ b
  
  不受约束的子类型不允许（需要初始化）
  提供初始值或显式数组
我不知道2件事：
1. 我有File_Name：String;因为我希望能够写入不同的文件。所以我想要一个通用的字符串，而不是像这样：
File_Name：CONSTANT String：=one_File_Only.dat
1. 将程序Open_Data保存在单独的广告和adb（用于正文）文件中会更好吗？
  
  非常感谢...
  
  全新。
  
  我修改了代码如下：
```
 与Ada.Sequential_IO; 
 
 PROCEDURE TEST1是
 
包Seq_Float_IO是新的Ada.Sequential_IO（Element_Type => Float）; 
 X_File，Y_File：Seq_Float_IO.File_Type; 
 Name_X：CONSTANT String：=domainvalues.dat; 
 Name_Y：CONSTANT String：=ordinatevalues.dat; 
 
 
过程Open_Data（File：in out Seq_Float_IO.File_Type; Name：in String）是
 
 BEGIN 
 
 begin 
 Seq_Float_IO.Open（
 File => File，
 Mode => Seq_Float_IO.Append_File，
 Name => Name_X）; 
例外
当Seq_Float_IO.Name_Error => 
 Seq_Float_IO.Create（
 File => File，
 Mode => Seq_Float_IO.Out_File，
 Name => Name_X）; 
 end; 
 
 END Open_Data; 
 
 
 x：CONSTANT Float：= 2.0; 
 
 
 BEGIN --main program 
 Open_Data（File => X_File，Name =&Name_X）; 
 Seq_Float_IO.Write（File => X_File，Item => x）; 
 Seq_Float_IO.Close（File => X_File）; 
 
 Open_Data（File => Y_File，Name => Name_Y）; 
 Seq_Float_IO.Write（File => Y_File，Item => x）; 
 Seq_Float_IO.Close（File => Y_File）; 
 
 END TEST1; 
  
```
  正如你所看到的那样
  <$ p $ （
  File =>文件，
  Mode => Seq_Float_IO.Append_File，
  Name => Name_X）; p> Seq_Float_IO.Open
  我已经把Name_X作为Name的参数，但这是不对的，因为我应该可以传入一个可以是Name_X或Name_Y的通用名称。抱歉的家伙，我不知道该把什么放在这里。
  
  我非常感谢你的帮助。谢谢
  解决方案
  在Ada中，普通的 String 字符串，如 File_Name ，必须是固定长度的;但是不同的字符串可以有不同的长度。
  
  您可以写
```
  S1：String：=1234; 
 S2：String：=12345; 
  
```
  在这种情况下，S1的长度是4，分配的长度必须是4。可写
```
  S1：=abcd; 
  
```
  但如果您尝试写入
```
  S1：=pqrst; 
  
```
  或
```
  S1：= S2; 
  
```
  你会得到一个 Constraint_Error p>
  
  对于子程序的字符串参数（例如 Open_Data ），String参数 Name 需要长度 - 当然还有值！呼叫中的实际参数。所以你可以说：
  $ b $ pre $ Open_Data（X_File，x.dat）; Open_Data（Y_File，a_very_long_name.dat）;
  您之前遇到过问题
  
  <$ p （File：in FileSeq_Float_IO.File_Type;
  Name：in String）是
  begin
  Seq_Float_IO.Open（File => File，
  Mode => Seq_Float_IO.Append_File，
  Name => ????）;
  
  我不愿意告诉你答案，所以考虑 File =>文件部分。第一个 File 是 Seq_Float_IO.Open 的形式参数的名字，第二个 File 是什么被传递，在这种情况下 Open_Data 的 File 参数。 / p>
  
  如果我指出我可以将上面的调用写成
```
  Open_Data（File => X_File，Name =>x.dat）; 
 Open_Data（File => Y_File，Name =>a_very_long_name.dat）; 
  
```
  This question is a follow-up of the post at
  
  Ada file operation: instantiation and exception
  
  about writing to files in Ada.
  
  I chose to place this question in a separate post so that it'll become visible to more people as I already accepted an answer on a slightly different issue (which was on exceptions in file handling) in that aforementioned post.
```
WITH Ada.Sequential_IO;
WITH Ada.Float_Text_IO;

PROCEDURE TEST is

package Seq_Float_IO is new Ada.Sequential_IO (Element_Type => Float);
X_File : Seq_Float_IO.File_Type;
File_Name : String;


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

BEGIN

   begin
      Seq_Float_IO.Open (
         File => File,
         Mode => Seq_Float_IO.Append_File,
         Name => File_Name );
   exception
      when Seq_Float_IO.Name_Error =>
      Seq_Float_IO.Create (
         File => File,
         Mode => Seq_Float_IO.Out_File,
         Name => File_Name);
   end;

END Open_Data;


x        : CONSTANT Float := 2.0;


BEGIN --main program
   Open_Data(X_File, "xvalues.dat");
   Seq_Float_IO.Write(File => X_File,Item => x);

   Seq_Float_IO.Close(File => X_File);
END TEST;
```
  On compiling the above I get an error as follows:
  1. X_File : Seq_Float_IO.File_Type;
    1. File_Name : String; |
      
      unconstrained subtype not allowed (need initialization) provide initial value or explicit array bounds
  I don't know 2 things:
  1. I have File_Name : String; as I want to be able to write to different files. So I want a general string and not something like:
  File_Name : CONSTANT String := "one_File_Only.dat"
  1. Would it be better to save the procedure Open_Data in separate ads and adb (for the body) files?
  Thanks a lot...
  
  NEW...
  
  I've modified the code as follows:
```
WITH Ada.Sequential_IO;

PROCEDURE TEST1 is

package Seq_Float_IO is new Ada.Sequential_IO (Element_Type => Float);
X_File, Y_File : Seq_Float_IO.File_Type;
Name_X : CONSTANT String := "domainvalues.dat";
Name_Y : CONSTANT String := "ordinatevalues.dat";


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

BEGIN

   begin
    Seq_Float_IO.Open (
         File => File,
         Mode => Seq_Float_IO.Append_File,
         Name => Name_X );
    exception
      when Seq_Float_IO.Name_Error =>
         Seq_Float_IO.Create (
            File => File,
            Mode => Seq_Float_IO.Out_File,
            Name => Name_X);
   end;

END Open_Data;


x        : CONSTANT Float := 2.0;


BEGIN --main program
   Open_Data(File => X_File, Name => Name_X);
   Seq_Float_IO.Write(File => X_File, Item => x);
   Seq_Float_IO.Close(File => X_File);

   Open_Data(File => Y_File, Name => Name_Y);
  Seq_Float_IO.Write(File => Y_File, Item => x);
  Seq_Float_IO.Close(File => Y_File);

END TEST1;
```
  As you see I have
```
Seq_Float_IO.Open (
             File => File,
             Mode => Seq_Float_IO.Append_File,
             Name => Name_X );
```
  I have put Name_X as the parameter that Name is taking but this is not right as I should be able to pass in a general name which can be either Name_X or Name_Y. Sorry guys, I can't figure out what to put here.
  
  I would much appreciate your help. Thanks
  解决方案
  The thing about plain String in Ada is that a particular string, like your File_Name, has to be fixed-length; but different Strings can be of different length.
  
  You can write
```
S1 : String := "1234";
S2 : String := "12345";
```
  in which case S1 is of length 4, and assignments to it have to be of length 4. You can write
```
S1 := "abcd";
```
  but if you try to write
```
S1 := "pqrst";
```
  or
```
S1 := S2;
```
  you will get a Constraint_Error.
  
  In the case of String parameters to subprograms, like your Open_Data, the String parameter Name takes on the length -- and of course the value! of the actual parameter in the call. So you can say
```
Open_Data (X_File, "x.dat");
Open_Data (Y_File, "a_very_long_name.dat");
```
  You were having problems earlier with
```
procedure Open_Data(File : in out Seq_Float_IO.File_Type; 
                    Name : in String) is
begin
   Seq_Float_IO.Open (File => File,
                      Mode => Seq_Float_IO.Append_File,
                      Name => ????);
```
  I'm reluctant to just tell you the answer, so -- consider the File => File part. The first File is the name of the formal parameter of Seq_Float_IO.Open and the second File is what is to be passed, in this case Open_Data's File parameter.
  
  It might help if I point out that I could have written the calls above as
```
Open_Data (File => X_File, Name => "x.dat");
Open_Data (File => Y_File, Name => "a_very_long_name.dat");
```
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在Ada中打开，写入和追加的过程 [英] Procedure to open, write and append in Ada

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