Re: Opening a File for Appending

[kst@alsys.com (Keith Thompson)]

In <3ejufu$g56@Starbase.NeoSoft.COM> dweller@Starbase.NeoSoft.COM (David Weller) writes:
> Um, in Ada95, one of the file modes is Append_File (for any of Text,
> Sequential, Wide, and Stream_IO files).
> 
> Appending a file in Ada83 is OS dependent (unless the POSIX binding
> supports this -- I'm not sure).

Yes it does, via the Form parameter of Text_IO.Open.

Here's a test/demo program; you can compile and execute it to find out
whether your implementation supports POSIX-style appending to a text file.

Note that it isn't necessary to explicitly "with" any POSIX packages;
POSIX specifies this behavior for the LRM-defined Text_IO package.

with Text_IO;
procedure Append_Test is
   File: Text_IO.File_Type;
   File_Name: constant String := "append.txt";
   Line1: constant String := "First line";
   Line2: constant String := "Second line";
   Ok: Boolean := True;
begin
   Text_IO.Create( File => File,
                   Mode => Text_IO.Out_File,
                   Name => File_Name );
   Text_IO.Put_Line(File, Line1);
   Text_IO.Close(File);

   Text_IO.Open( File => File,
                 Mode => Text_IO.Out_File,
                 Name => File_Name,
                 Form => "Append => True" );
   Text_IO.Put_Line(File, Line2);
   Text_IO.Close(File);

   declare
      S: String(1 .. 100);
      Last: Natural;
   begin
      Text_IO.Open( File => File,
                    Mode => Text_IO.In_File,
                    Name => File_Name );
      Text_IO.Get_Line(File, S, Last);
      if S(S'First .. Last) /= Line1 or Text_IO.End_Of_File(File) then
         Ok := False;
      else
         Text_IO.Get_Line(File, S, Last);
         if S(S'First .. Last) /= Line2 then
            Ok := False;
         end if;
      end if;
   exception
      when others =>
         Ok := False;
   end;

   begin
      Text_IO.Delete( File );
   exception
      when others => 
         Ok := False;
   end;

   if Ok then
      Text_IO.Put_Line("This implementation supports POSIX-style");
      Text_IO.Put_Line("appending to a text file via the Form parameter.");
   else
      Text_IO.Put_Line("This implementation does not support POSIX-style");
      Text_IO.Put_Line("appending to a text file via the Form parameter,");
      Text_IO.Put_Line("or some other problem occurred.");
   end if;

end Append_Test;

-- 
Keith Thompson (The_Other_Keith)  kst@thomsoft.com (kst@alsys.com still works)
TeleSoft^H^H^H^H^H^H^H^H Alsys^H^H^H^H^H Thomson Software Products
10251 Vista Sorrento Parkway, Suite 300, San Diego, CA, USA, 92121-2718
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