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From: carl@CITHEX.CALTECH.EDU.UUCP
Newsgroups: mod.computers.vax
Subject: Re: reassignment in VMS
Message-ID: <870203130348.017@CitHex.Caltech.Edu>
Date: Tue, 3-Feb-87 16:04:02 EST
Article-I.D.: CitHex.870203130348.017
Posted: Tue Feb  3 16:04:02 1987
Date-Received: Thu, 5-Feb-87 03:19:41 EST
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>My (FORTRAN) program  writes graphics to the tektronics terminal.
>It does so by assigning a channel to something and QIOW to this channel:

>        int2 = sys$assign('ugdevice',ddacn,,)           ! hook for file output
>        if(.not. int2) int2 = sys$assign('tt',ddacn,,)  ! if not file, terminal
>.........
>        sys$qiow(,%val(ddacn),.....)

>Now, when I 'assign a.a ugdevice', it bypasses first sys$assign (int2 is appa-
>rently non-zero, second assign takes place, with the effect that output goes
>to the terminal (tt)). If I 'assign dua0:[pzk]a.a ugdevice', the ddacn channel
>is assigned to (probably) dua0:[pzk]a.a , but now the sys$qiow returns non-zero
>status.
>Could anybody explain this to me?
>My goal is to redirect the output of the program to the file.
>I am relatively new to VMS, so please don't say it should be obvious :^)

But it IS obvious:  SYS$ASSIGN assigns a channel to a DEVICE, not to a FILE.
When you 'assign a.a ugdevice', the first call to SYS$ASSIGN returns the
error code SS$_IVDEVNAM, which has the associated message text:
"%SYSTEM-F-IVDEVNAM, invalid device name": i.e., A.A is not a device.  When
you 'assign dua0:[pzk]a.a ugdevice', SYS$ASSIGN assigns a channel to DUA0:.
However, when you try to write to the device using SYS$QIOW, it turns out
that you don't have the privs to write directly to the disk (and a good
thing, too; if you had, the file structure on the disk would have become
unreadable).  You've got three choices:  1)  You can use the QIO disk ACP
interface (not recommended for a neophyte); 2) You can use calls to RMS
(somewhat easier for a neophyte, but also somewhat complex and probably
not necessary); or 3)  You can use the FORTRAN OPEN and WRITE statements
to do the I/O (probably your best bet).