Reading sequential data from Ada.Text_Io.Standard_Input?

Reading sequential data from Ada.Text_Io.Standard_Input?

[David J. Fiander]

So, I want to read from standard input, using Ada.Sequential_Io.
I've got

	declare
	    type Byte is mod 256; for Byte'Size use 8;
	    package Byte_Io is new package Ada.Sequential_Io(Byte);

	    Ch: Byte;
	begin
	    Byte_Io.Read(Text_Io.Standard_Input, Ch);
	    -- process the byte;
	end;

which clearly doesn't work, since Text_Io.Standard_Input is most
definitely not a Byte_Io.File_Type.  So I try

	Byte_Io.Read(Byte_Io.File_Type(Text_Io.Standard_Input), Ch);

at which Gnat reports "ambiguous operand", since Standard_Input
is either a Text_Io.File_Type or a Text_Io.File_Access and Gnat
can't figure out which I want.  So I try

	Byte_Io.Read(Byte_Io.File_Type(Text_Io.File_Type'(Text_Io.Standard_Input)), Ch);

which is certainly a mouthful, but also doesn't work.  Gnat
reports

	invalid conversion, not compatible with private type
		"Ada.Text_Io.File_Type" 

thereby informing me that, now that it knows what I want to do,
it's decided that I can't get there from here.

So, what, if anything, is the magic incantation to read raw data
from standard input?

- David

Re: Reading sequential data from Ada.Text_Io.Standard_Input?

[Michael Paus]

davidf@worf.mks.com (David J. Fiander) wrote:
> So, I want to read from standard input, using Ada.Sequential_Io.
> 
[...]
> So, what, if anything, is the magic incantation to read raw data
> from standard input?

The key to this kind of problem is to use the new Ada 95 streams
facility. Have a look at "A.12 Stream Input-Output". You can get
a stream access value which is associated with Standard_Input with
a declaration like this:

  S  : Ada.Text_IO.Text_Streams.Stream_Access
       := Ada.Text_IO.Text_Streams.Stream(Ada.Text_IO.Standard_Input);

You will need to with 
Ada.Text_IO, Ada.Text_IO.Text_Streams and Ada.Streams.Stream_IO
in order to get that working.

Have fun

Michael

PS: If you are interested I can send you a little example with a writer
application which writes a data structure to a stream which is
associated with standard output and a reader application which recreates
this data structure from a stream which is connected to standard input.
On UNIX you might then execute these apps like

> writer | reader

which means that the data produced by writer is piped into reader.

-- 
------------------------------------------------------------------------
--Dipl.-Ing. Michael Paus   (Member: Team Ada)
--University of Stuttgart, Inst. of Flight Mechanics and Flight Control
--Forststrasse 86, 70176 Stuttgart, Germany
--Phone: (+49) 711-121-1434  FAX: (+49) 711-634856
--Email: Michael.Paus@ifr.luftfahrt.uni-stuttgart.de (NeXT-Mail welcome)

Re: Reading sequential data from Ada.Text_Io.Standard_Input?

[Robert Dewar]

David asks how to read raw data from standard input. The answer is to
use Stream_IO, it's all setup for that.

You could also create an appropriate sequential_io descriptor, have a look
at package

package Ada.Sequential_IO.C_Streams is

in file s-siocst.ads, which permits opening a sequent file given a C
stream identifier (there are analogous packages for all the I/O packages
in GNAT).

You certainly cannot expect success following the line you were trying.
File types are completely different for different I/O packages, and here
there is no reason to think you could convert one to another. GNAT does
not "know what you want to do", as far as it is concerned you are trying
a totally junk type conversion from one type to a completely unrelated
type that makes no sense at all. 

Re: Reading sequential data from Ada.Text_Io.Standard_Input?

[Robert A Duff]

In article <4rsibv$2mo@ia.mks.com>,
David J. Fiander <davidf@worf.mks.com> wrote:
>So, what, if anything, is the magic incantation to read raw data
>from standard input?

Try Ada.Text_IO.Text_Streams (or whatever it's called).

- Bob