[Info-vax] proper format for JPEG files

[Jose Baars]

On Jul 26, 5:41 am, Hein RMS van den Heuvel
<heinvandenheu... at gmail.com> wrote:

> Of course not. And that's not what he wrote.

Sorry.

> IF you call SYS$MODIFY you can instruct RMS to use other attributes.
> $REWIND is optional.

I never came across sys$modify before.
Found an example using sys$modify on Internet,
fix_saveset.c.  I also found out you can not open
the file shared or else the mrs will not get changed,
and I couldn't get it to change record attributes either,
but maybe that is not the intention.
It's hard to use undocumented functions, but interesting
to play with, thanks!

>Paul >That will only work if you have write access to the file.
 Definitely, and that applies to using sys$modify as well.


> You may also want to try use UDF format and read more bytes per get,
> yet retaining read-ahead (unlike SYS$READ)

I'll have to play around with that to see, thanks for the tip!

>
> Would those perhaps be the line terminator characters?
>

I checked again, and yes they were.

>
> The CRTL does NOT use RMS record mode SYS$GET call for simple files.
> It will use RMS SYS$READ and de-block and optionally corrupt data on
> its own.

So not everybody was in agreement on the definition of RMS.

Sorry to have this discussion go in this direction. In
my opinion the original question can be answered like so:

'Binary' files (jpg,gif,pdf...) can be stored on VMS in both
fix512 and stream_lf format, but reading these files can pose
problems if they have been transferred wrongly and/or
have been mutilated afterwards on the VMS system, where
fix512 has a slightly smaller risk of suffering from
miscreation or mutilation.