Re: Ada.Streams.Stream_IO.File_Type

["Nick Roberts" <nickroberts@blueyonder.co.uk>]

"Craig Carey" <research@ijs.co.nz> wrote in message
news:mt7chvs7heoihdv7a3a6psh5h8v1b46i2i@4ax.com...

> On Tue, 15 Jul 2003 13:30:33 -0500, "David C. Hoos"
> > The package Ada.TextIO.Text_Streams allows one
> > to obtain the stream object corresponding to the
> > standard input -- i.e.:
> >
> > Standard_Input_Stream :
> >    Ada.Text_IO.Text_Streams.Stream_Access :=
> >       Ada.Text_IO.Text_Streams.Stream
> >          (Ada.Text_IO.Standard_Input);
>
> This comment is not on Text_Streams:
> ...
> A fix would be to add this next line to Ada.Streams.Stream_IO:
>
>     function Standard_Input return File_Type;
>
> Anyone know why it is not in there already?

Yes! Because you can use the technique given by David Hoos.

> Portable Ada programs handling piping or CGI I/O may
> need that unless using C (etc.).

If an Ada program which is a client of the Common Gateway Interface (CGI) --
used by various web (HTTP) server programs to allow 'client' programs to
dyamically generate web pages -- implements the interface by directly
interacting with its 'standard input' and 'standard output' (in the Unix
sense), it must be considered essentially non-portable.

Such a program may be portable among Unix-based (maybe POSIX-based)
environments, but generally not otherwise. In this case, the Ada program
might just as well import the appropriate C functions to read or write bytes
directly; I would suggest that in most cases interaction is all text-based
anyway, and it would be easier and better to use Ada.Text_IO (and if the Ada
implementation isn't able to handle line termination correctly, I would say
that's a major problem with the implementation).

For true portability, an Ada program which is intended to be used as a CGI
client should put everything specific to interfacing with the environment
into a package (named 'CGI' perhaps ;-) and I'm fairly sure at least one
such package is available. To port the program to a (significantly
different) environment, this package (only) needs to be reimplemented. This
would provide further advantageous isolation (such as from changes to the
HTTP header that a CGI client program should output).

> ...
> Currently GNAT 3.15's Text_IO.Text_Streams feature
> stops reading, on encountering a ASCII.SUB character
> (= character 10#26#).

That's just a problem with GNAT, isn't it?

> Presumably they don't like the RM's design.

Presumably it's a simple bug in GNAT 3.15. It's quite reasonable (in my
'humble' opinion :-) for text-oriented I/O (except Look_Ahead and
Get_Immediate) to stop on a SUB, but not stream-oriented I/O. The RM permits
this; I think it would often be handy for Ada implementations to provide
options with regard to line, page, and file termination.

--
Nick Roberts
Jabber: debater@charente.de [ICQ: 159718630]