From: hoffman@xdelta.zko.dec.nospam
Sent: Friday, February 02, 2001 5:02 PM
To: Info-VAX@Mvb.Saic.Com
Subject: Re: How to detect if VT320 has local printer attached.

In article <95ettp$c7l$1@nnrp1.deja.com>, Fatz <fatz_nyc@my-deja.com> writes:
:If the escape sequence is sent to the terminal when there's no printer, the 
:app "hangs".
:
:We need a way of determining if the terminal physically has a printer
:attached to it before trying to print to it.

  Simply ask the terminal if it has a printer attached, and it will
  tell you.  Attached is some (old) C code that should be helpful, 
  albiet somewhat crufty -- I've done a very quick and cursory update 
  to get the code to compile under Compaq C, but have not executed the
  code or otherwise tested it in a long time...

 --------------------------- pure personal opinion ---------------------------
   Hoff (Stephen) Hoffman   OpenVMS Engineering   hoffman#xdelta.zko.dec.com


#pragma module EXAMPLE "SRH X1.0-000"

/*
** Copyright 2000 Compaq Computer Corporation
*/

/*
**++
**  Facility:
**
**	Examples
**
**  Version: V1.0
**
**  Abstract:
**
**	Example of working with the $QIO Extended Read
**
**  Author:
**	Steve Hoffman
**
**  Creation Date:  1-Jan-1990
**
**  Modification History:
**                  2-Feb-2001  Compaq C updates, Copyright
**
**--
*/
#include <descrip.h>
#include <iodef.h>
#include <ssdef.h>
#include <starlet.h>
#include <stdio.h>
#include <string.h>
#include <stsdef.h>
#include <trmdef.h>

open_target( char *trgdev, unsigned short int *chn )
    {
    unsigned long int retstat;
    struct dsc$descriptor trgdsc;

    trgdsc.dsc$w_length = strlen( trgdev );
    trgdsc.dsc$b_dtype = DSC$K_DTYPE_T;
    trgdsc.dsc$b_class = DSC$K_CLASS_S;
    trgdsc.dsc$a_pointer = trgdev;

    retstat = sys$assign( &trgdsc, chn, 0, 0, 0 );
    if (!$VMS_STATUS_SUCCESS( retstat )) return retstat;

    return retstat;
    }

close_target( unsigned short int chn )
    {
    unsigned long int retstat;

    retstat = sys$dassgn( chn );
    if (!$VMS_STATUS_SUCCESS( retstat )) return retstat;

    return retstat;
    }

write_target_with_reply( unsigned short int chn,
    char *wrbuf, char *rdbuf )
    {
    unsigned long int retstat;
    struct qioiosb
	{
        short retstat;
	short terminator_offset;
	char  terminator_char;
	char  reserved;
	char  terminator_length;
	char  cursor_position;
	} rdiosb, wriosb;
    
    struct itemlist_3
	{
	unsigned short int itmlen;
	unsigned short int itmcod;
	void *itmbuf;
	void *itmrla;
	} itmlst[]= 
	{
	    {
	    0, TRM$_ESCTRMOVR, (void *) 64, 0
	    },
	    {
	    0, TRM$_MODIFIERS, (void *)
	    (TRM$M_TM_ESCAPE | TRM$M_TM_TRMNOECHO | 
	    TRM$M_TM_NOFILTR | TRM$M_TM_NORECALL),
	    0
	    }
	};

    retstat = sys$qio( 0, chn,
	IO$_READVBLK | IO$M_EXTEND, &rdiosb, 0, 0,
	rdbuf, 255, 0, 0, itmlst, sizeof(itmlst));
    if (!$VMS_STATUS_SUCCESS( retstat )) return retstat;

    retstat = sys$qiow( 0, chn,
	IO$_WRITEVBLK, &wriosb, 0, 0,
	wrbuf, strlen(wrbuf), 0, 0, 0, 0);
    if (!$VMS_STATUS_SUCCESS( retstat )) return retstat;
    retstat = sys$synch(0, &wriosb );

    retstat = sys$synch(0, &rdiosb );

    return retstat;
    }


main()
    {
    unsigned long int retstat;
    unsigned short int target_chan;
    char *target_device = "SYS$OUTPUT";
    char target_reply[255];
    unsigned long int *rply;
    
    retstat = open_target( target_device, &target_chan );
    if (!$VMS_STATUS_SUCCESS( retstat )) return retstat;

    retstat = write_target_with_reply( target_chan, "\033[?15n", target_reply );
    if (!$VMS_STATUS_SUCCESS( retstat )) return retstat;

    rply = (void *) &target_reply[2];
    switch (*rply )
	{
	case '?10n':
	    printf("Printer ready\n");
	    break;
	case '?11n':
	    printf("Printer not ready\n");
	    break;
	case '?13n':
	    printf("No printer\n");
	    break;
	case '?18n':
	    printf("Printer busy\n");
	    break;
	default:
	    printf("Unrecognized response\n");
	    break;
	}

    retstat = close_target( target_chan );
    if (!$VMS_STATUS_SUCCESS( retstat )) return retstat;

    return SS$_NORMAL;
    }