Ada streams

Ada streams

[Daniel Vencler]

	Hi, I want to ask you where I can get good explanation
what are and how to use (and when) ada streams. There are few
ada tutorials on net but not single one of them mentions streams.


					Best regards,
					Daniel Vencler

Re: Ada streams

[John B. Matthews]

In article <cpoq0o$vuk$1@sunce.iskon.hr>,
 Daniel Vencler <danielMAKNI@geofoto.hr> wrote:

> 	Hi, I want to ask you where I can get good explanation
> what are and how to use (and when) ada streams. There are few
> ada tutorials on net but not single one of them mentions streams.
> 
> 
> 					Best regards,
> 					Daniel Vencler

Warren Gay has added a section on streams to "The Big Online Book of 
Linux Ada Programming":

<http://www.pegasoft.ca/resources/boblap/11.html#11.12>

-- 
John
jmatthews at wright dot edu
www dot wright dot edu/~john.matthews/

Re: Ada streams

[Nick Roberts]

Daniel Vencler wrote:

> Hi, I want to ask you where I can get good explanation what are and
> how to use (and when) ada streams. There are a few ada tutorials on 
> the net but not single one of them mentions streams.

To answer the question of when to use streams, the brief answer is: in
almost any situation where you are not using text I/O (using the
package Ada.[Wide_]Text_IO and its children), and a few besides.

Consider a variety of different file types in common use today: the
JPEG pictorial image format; the PKWare ZIP compression format; the
Microsoft word processor DOC format; the HTML (HyperText Markup
Language) format used for web pages. For the HTML format, you may wish
to use Ada.Text_IO, but for some rather esoteric (and unfortunate)
technical reasons, you might want to use Ada.Streams.Stream_IO. For
all the others, you will certainly want to use Ada.Streams.Stream_IO.

Similarly, streams will be used to perform packet-based network
communications, and possibly some other kinds of communications. A
package will provide a stream into which you write data into a packet
(it's payload), prior to sending the packet, as well as a stream to
read the (payload) data out of a packet when it is received. A device
driver (interface) package for a printer, say, may well provide a
stream into which you write the data to be sent to the printer.

There are certain rare situations in which you might want to streams
for a purpose other than I/O, for example a memory buffer.

Section 11.12 of the Big Online Book of Linux Ada Programming, as
pointed to by another replier, seems to give quite a good introduction
into how to use streams.

Maybe I should say a quick word on what a stream is. In practice, a
stream is a sequence of bytes -- which are called 'octets' formally --
which comprise the binary representation of one or a sequence of
variable values. The values can be of any type. The bytes do not
normally encode the type (they do if you use the Output procedure on a
tagged type) of each value, nor do they encode what the sequence of
values was (if there was more than one value). You simply have to know
these things to read the values back again correctly. The binary
representation of each type will depend on the target machine, and is
in any case implementation specific. These means that, unless you take
special precautions, you must use the same compiler and target machine
to read a file as you used to write the file in the first place.

Ada.Streams.Stream_IO can be used to read binary files in a standard
format (such as JPEG, ZIP, or DOC), provided you know the exact
details of the formats of all the data types in the format, and use
representation clauses or other methods to read those data types
correctly.

I hope this is helpful. I think you'll have to ask more specific
questions to get more detailed answers.

-- 
Nick Roberts

Re: Ada streams

[tmoran]

>Maybe I should say a quick word on what a stream is. In practice, a
>stream is a sequence of bytes -- which are called 'octets' formally --
>which comprise the binary representation of one or a sequence of
>variable values. The values can be of any type. The bytes do not
  Ada.Streams gives a standardized way for the designer of an object
to supply "IO" routines for that object.  Thus Bitmap'Write might in
fact create a JPEG compressed version of an in-memory bitmap array.
If a user creates a composite object he automatically gets an IO
routine that will make the necessary calls for the component parts.
Thus given
  type Stereo_Image_Type is record
    Left, Right : Bitmap;
  end record;
Stereo_Image_Type'Write(F,Scene); will automatically call Bitmap'Write
on the Left and Right images (unless overridden, of course).
  Ada.Streams does not require you to use Ada.Streams.Stream_IO, however,
so you can also create specialized children of Root_Stream_Type which
don't do IO, but rather something else.  You might just want the
Stream_Element_Count of the size of the object, or perhaps a checksum of
its Stream_Element_Array representation.

Re: Ada streams

[David C. Hoos]

One answer to the "when" question is "when you want to read and
write heterogeneous data to a file."

Such an example may be found at my web site

ftp://ada95.com/pub/pet_store.tar.gz
or
ftp://ada95.com/pub/pet_store.tgz

In addition to demonstrating streams, it demonstrates the use of
some of the object-oriented features of Ada95 -- e.g. derivation
of concrete types from abstract parent types.


----- Original Message ----- 
From: "Daniel Vencler" <danielMAKNI@geofoto.hr>
Newsgroups: comp.lang.ada
To: <comp.lang.ada@ada-france.org>
Sent: Wednesday, December 15, 2004 1:43 AM
Subject: Ada streams


> Hi, I want to ask you where I can get good explanation
> what are and how to use (and when) ada streams. There are few
> ada tutorials on net but not single one of them mentions streams.
> 
> 
> Best regards,
> Daniel Vencler
> 
> _______________________________________________
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> comp.lang.ada@ada-france.org
> http://www.ada-france.org/mailman/listinfo/comp.lang.ada
>