Portable way to read/write from a binary file?

Portable way to read/write from a binary file?

[Dale Stanbrough]

Is there a _portable_ way to read/write from a binary file using only
Ada83 or Ada94 I/O routines?

I would like to be able to read the individual bytes from a file, as can
be achieved using Unix read/write.

Dale
-------------------------------------------------------------
Dale Stanbrough, RMIT, Melbourne, Australia, dale@rmit.edu.au
GNU Ada Compiler (GNAT) => the best $0 you'll ever spend.
Available for DOS, Linux, OS/2, Sun Sparc, Sun Solaris, ...
Coming to a GNU supported platform near you soon...

Re: Portable way to read/write from a binary file?

[Robert Dewar]

sequential_io instantiated for a byte or character type may work, but is
not guaranteed, and may well be gruseomely slow.

best get is just to use pragma interface and use the appropriate unix
routines directly, whjy not>

Re: Portable way to read/write from a binary file?

[Dale Stanbrough]

Subject: Re: Portable way to read/write from a binary file?
From: Robert Dewar, dewar@cs.nyu.edu
Date: 13 Sep 1994 23:51:00 -0400
In article <355rv4$eg8@gnat.cs.nyu.edu> Robert Dewar, dewar@cs.nyu.edu writes:
>sequential_io instantiated for a byte or character type may work, but is
>not guaranteed, and may well be gruseomely slow.
>
>best get is just to use pragma interface and use the appropriate unix
>routines directly, whjy not>

Because I wanted a portable solution that wasn't tied to a particular
operating system. It may be that there are comparable routines on _all_
operating systems, but it still (potentially) leaves you with code to change
when porting.

Dale
-------------------------------------------------------------
Dale Stanbrough, RMIT, Melbourne, Australia, dale@rmit.edu.au
GNU Ada 94 (GNAT) => the best $0 you'll ever spend.
Available for DOS, Linux, OS/2, Sun Sparc, Sun Solaris, ...
Coming to a GNU supported platform near you soon...

Re: Portable way to read/write from a binary file?

[Robert Dewar]

There is a set of C/Unix/ANSIC routines (some intersection) that is VERY
portable, as portable as anything else. The GNU porting guide (perhaps Richard
can give a better reference) has details on what can typically be counted on.

Re: Portable way to read/write from a binary file?

[Keith Thompson @pulsar]

In <355kao$38d@goanna.cs.rmit.oz.au> Dale Stanbrough <dale@goanna.cs.rmit.edu.au> writes:
> Is there a _portable_ way to read/write from a binary file using only
> Ada83 or Ada94 I/O routines?
> 
> I would like to be able to read the individual bytes from a file, as can
> be achieved using Unix read/write.

For Ada 83, POSIX_IO is reasonably portable (among implementations that
support it).

For Ada 94 (assuming X=4 8-)}), I think Stream_IO does what you want.

-- 
Keith Thompson (The_Other_Keith)  kst@alsys.com
TeleSoft^H^H^H^H^H^H^H^H Alsys, Inc.
10251 Vista Sorrento Parkway, Suite 300, San Diego, CA, USA, 92121-2718
/user/kst/.signature: I/O error (core dumped)

Re: Portable way to read/write from a binary file?

[Lee_Robert_Willis]

>sequential_io instantiated for a byte or character type may work, but is
>not guaranteed, and may well be gruseomely slow.

FWIW: This will not work under VMS.  (Been there, tried that)

   -lee     Lee_Robert_Willis@cup.portal.com
   

Re: Portable way to read/write from a binary file?

[R_Tim_Coslet]

>In article <355rv4$eg8@gnat.cs.nyu.edu> Robert Dewar, dewar@cs.nyu.edu writes:
>>sequential_io instantiated for a byte or character type may work, but is
>>not guaranteed, and may well be gruseomely slow.
>>
>>best get is just to use pragma interface and use the appropriate unix
>>routines directly, whjy not>
>
>Because I wanted a portable solution that wasn't tied to a particular
>operating system. It may be that there are comparable routines on _all_
>operating systems, but it still (potentially) leaves you with code to change
>when porting.
>
>Dale
>-------------------------------------------------------------
>Dale Stanbrough, RMIT, Melbourne, Australia, dale@rmit.edu.au
>GNU Ada 94 (GNAT) => the best $0 you'll ever spend.
>Available for DOS, Linux, OS/2, Sun Sparc, Sun Solaris, ...
>Coming to a GNU supported platform near you soon...

Or maybe the code will eventually be used in an embedded environment that has
NO operating system of any kind, just a small Ada Runtime customized
to the hardware environment.

                                        R. Tim Coslet

Usenet: R_Tim_Coslet@cup.portal.com
        technology, n.  domesticated natural phenomena

Re: Portable way to read/write from a binary file?

[Dale Stanbrough]

In article <Cw717J.66q@alsys.com> , kst@alsys.com writes:
>For Ada 94 (assuming X=4 8-)}), I think Stream_IO does what you want.
>

Unfortunately not (as I read it!)
Each object in a stream has a tag appended to it so that the 
procedure S'Class'Read can reconstruct the value from the tag 
contained within the stream (13.13.2.14).
As well the representation of stream elements is implementation
defined (13.13.2.17)

The best solution seems to be to use pragma import or use the
Posix_IO package.

Dale
-------------------------------------------------------------
Dale Stanbrough, RMIT, Melbourne, Australia, dale@rmit.edu.au
GNU Ada 94 (GNAT) => the best $0 you'll ever spend.
Available for DOS, Linux, OS/2, Sun Sparc, Sun Solaris, ...
Coming to a GNU supported platform near you soon...

Re: Portable way to read/write from a binary file?

[Bob Duff]

In article <35iuqj$5dj@goanna.cs.rmit.oz.au>,
Dale Stanbrough  <dale@goanna.cs.rmit.edu.au> wrote:
>In article <Cw717J.66q@alsys.com> , kst@alsys.com writes:
>>For Ada 94 (assuming X=4 8-)}), I think Stream_IO does what you want.
>>
>
>Unfortunately not (as I read it!)
>Each object in a stream has a tag appended to it so that the 
>procedure S'Class'Read can reconstruct the value from the tag 
>contained within the stream (13.13.2.14).

No.  S'Class'Read and S'Class'Write do not generally read and write tags.
(S'Class'Input and S'Class'Output do.)
Furthermore, if you're not using tagged types, then no tags are written
or read by any of these things.

The Stream_IO package and the streams stuff in 13.13 are definitely
intended for doing binary I/O.  A typical case is where the various
types are *not* tagged (or discriminated or unconstrained arrays or
anything fancy like that), and S'Write and S'Read can be used directly.
You won't get tags or other dope mixed in with your data.

>As well the representation of stream elements is implementation
>defined (13.13.2.17)

True, but in practice that's not a big problem.  After all, the
representation of Sequential_IO, Direct_IO, and Text_IO files are also
implementation defined.  You have to trust the implementation to use a
"reasonable" representation.  13.13.2(18-20) give advice about what a
reasonable representation is.  Most languages that support binary I/O
are similar in this regard.  (Not COBOL, though.)

>The best solution seems to be to use pragma import or use the
>Posix_IO package.

Note that Posix_IO, or pretty much any other I/O package, also has an
implementation-defined representation of the data.
-- 
Bob Duff                                bobduff@inmet.com
Oak Tree Software, Inc.
Ada 9X Mapping/Revision Team (Intermetrics, Inc.)

Re: Portable way to read/write from a binary file?

[Dale Stanbrough]

I wrote:
>In article <Cw717J.66q@alsys.com> , kst@alsys.com writes:
>>For Ada 94 (assuming X=4 8-)}), I think Stream_IO does what you want.
>>
>
>Unfortunately not (as I read it!)
>Each object in a stream has a tag appended to it so that the 
>procedure S'Class'Read can reconstruct the value from the tag 
>contained within the stream (13.13.2.14).

Keith Thompson emailed a correction to this; what I said is true only
for tagged types.
I had previously skimmed over streams in the LRM and produced a particularly 
premature perception of how it performs. When Keith posted his original reply
I opened up the LRM to the section I quoted - the only bit which did agree with
how I thought it worked! (Damn!   !:-(   ).

So here's a question that I couldn't find the answer to (no more posturing
about how it does work from me! :-). Does a stream of heterogenous scalar
elements have any encoding so that you can decide what the byte stream
represents, or does the format of the data in a stream have to be previously
determined?

Dale
-------------------------------------------------------------
Dale Stanbrough, RMIT, Melbourne, Australia, dale@rmit.edu.au
GNU Ada 94 (GNAT) => the best $0 you'll ever spend.
Available for DOS, Linux, OS/2, Sun Sparc, Sun Solaris, ...
Coming to a GNU supported platform near you soon...