Q: Index value in case of Ada.Streams.Stream_IO.End_Error

Q: Index value in case of Ada.Streams.Stream_IO.End_Error

[Gautier]

Hello!

Is there a RM-documented way to know the Index of a Ada.Streams.Stream_IO.File_Type
when it knocks the end of a file at reading it ?
I did not see a mention of what value the Index should have in that situation in
the RM 95, so for the moment I prefer to reread a partial buffer byte per byte
in order to know what has been effectively read. But maybe - hopefully - there
is a better way.

   procedure Read_buffer is

     procedure Byte_per_byte is
     begin
       for i in inbuf'Range loop
         Byte'Read( Ada.Streams.Stream_IO.Stream(infile), inbuf(i) );
         readpos:= readpos + 1;
       end loop;
     exception
       when Ada.Streams.Stream_IO.End_Error => null;
       -- nothing, we just reached EOF again
     end Byte_per_byte;

     start: Ada.Streams.Stream_IO.Positive_Count:=
              Ada.Streams.Stream_IO.Index(infile);
   begin
     readpos:= 0;
     begin
       IO_buf'Read( Ada.Streams.Stream_IO.Stream(infile), inbuf );
       readpos:= inbuf'Length;
     exception
       when Ada.Streams.Stream_IO.End_Error =>
         -- End reached, re-read in order to know the last position
         Ada.Streams.Stream_IO.Set_Index(infile, start);
         Read_buffer.Byte_per_byte;
     end;
   end Read_buffer;

Thanks in advance!
_______________________________________________________________
Gautier         -- http://www.mysunrise.ch/users/gdm/index.htm
Ada programming -- http://www.mysunrise.ch/users/gdm/gsoft.htm

NB: For a direct answer, e-mail address on the Web site!

Re: Q: Index value in case of Ada.Streams.Stream_IO.End_Error

[Jean-Pierre Rosen]

Gautier a �crit :
> Hello!
> 
> Is there a RM-documented way to know the Index of a 
> Ada.Streams.Stream_IO.File_Type
> when it knocks the end of a file at reading it ?
out parameter Last in function Read...

This gives you the number of bytes actually read.
-- 
---------------------------------------------------------
            J-P. Rosen (rosen@adalog.fr)
Visit Adalog's web site at http://www.adalog.fr

Re: Q: Index value in case of Ada.Streams.Stream_IO.End_Error

[Gautier]

Jean-Pierre Rosen:

>> Is there a RM-documented way to know the Index of a 
>> Ada.Streams.Stream_IO.File_Type
>> when it knocks the end of a file at reading it ?

> out parameter Last in function Read...
> 
> This gives you the number of bytes actually read.

You mean the _procedure_ Read, from Stream_IO ?

   procedure Read (File : in File_Type;
                   Item : out Stream_Element_Array;
                   Last : out Stream_Element_Offset);

Nice, but for my buffer I need to use the Read _attribute_ (13.13.2).

procedure S'Read( Stream : access Ada.Streams.Root_Stream_Type'Class;
                   Item : out T)

No "Last" there... If I try:

         IO_buf'Read( Ada.Streams.Stream_IO.Stream(infile), inbuf, last );

a compiler says as expected:
unz_io.adb:55:67: unexpected argument for "Read" attribute

Hence my question.
Mmmh, unless I redefine my buffer as a Stream_Element_Array.
Are you assuming that ?
_______________________________________________________________
Gautier         -- http://www.mysunrise.ch/users/gdm/index.htm
Ada programming -- http://www.mysunrise.ch/users/gdm/gsoft.htm

NB: For a direct answer, e-mail address on the Web site!

Re: Q: Index value in case of Ada.Streams.Stream_IO.End_Error

[Jean-Pierre Rosen]

Gautier a �crit :
> Jean-Pierre Rosen:
> 
>>> Is there a RM-documented way to know the Index of a 
>>> Ada.Streams.Stream_IO.File_Type
>>> when it knocks the end of a file at reading it ?
> 
>> out parameter Last in function Read...
>>
>> This gives you the number of bytes actually read.
> 
> You mean the _procedure_ Read, from Stream_IO ?
> 
>   procedure Read (File : in File_Type;
>                   Item : out Stream_Element_Array;
>                   Last : out Stream_Element_Offset);
> 
> Nice, but for my buffer I need to use the Read _attribute_ (13.13.2).
> 
If you use 'Read, and there is not enough bytes left in the file, then 
your file is corrupted. You will get End_Error.
Now, if you want to analyze what happened, here is what you can do:
1) before calling 'Read, get the current index (function Index)
2) Do a T'Read
3) If you get End_Error, do a Set_Index to return where you were, and 
use the Read procedure to get the corresponding array of bytes.
Then it's up to you...
-- 
---------------------------------------------------------
            J-P. Rosen (rosen@adalog.fr)
Visit Adalog's web site at http://www.adalog.fr

Re: Q: Index value in case of Ada.Streams.Stream_IO.End_Error

[Gautier]

Jean-Pierre Rosen:

> If you use 'Read, and there is not enough bytes left in the file, then 
> your file is corrupted. You will get End_Error.
> Now, if you want to analyze what happened, here is what you can do:
> 1) before calling 'Read, get the current index (function Index)
> 2) Do a T'Read
> 3) If you get End_Error, do a Set_Index to return where you were, and 
> use the Read procedure to get the corresponding array of bytes.
> Then it's up to you...

Fine, it's what I'm doing currently (cf the lines of code in my 1st post).
But since the buffer in question happens to be a byte array,
I'll switch to the Read procedure and just define the buffer as a
Stream_Element_Array.
Thanks
_______________________________________________________________
Gautier         -- http://www.mysunrise.ch/users/gdm/index.htm
Ada programming -- http://www.mysunrise.ch/users/gdm/gsoft.htm