From: att!mtunb!dmt@ucbvax.berkeley.edu (Dave Tutelman)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Printer can't backspace (was Help with IBM Graphics Printer)
Date: 13 Sep 88 13:40:47 GMT
Summary: Here's a filter to solve the problem.

randy@umn-cs.cs.umn.edu (Randy Orrison) writes:
>Could someone tell me how to set up my IBM Personal Computer Graphics
>Printer so that it understands what a backspace is, instead of just
>ignoring it? ...  I have a big document with
>lots of _^Hs_^Ht_^Hu_^Hf_^Hf in it that I would really like to be able
>to print.  It also has IBM printer specific escape codes in it, so I can't
>just use a different printer.

Gee, that's the second such request I've seen this morning.  I had the
same problem last week with my AT&T 473 printer (a "clone"), and wrote a
little filter that fixes the problem.  It scans through a line at a
time, and converts overstrikes to full-line overstrikes; backspace may
not work on my printer, but carriage return does.

I've attached the C source.  I compiled it using Turbo 1.0, but it's
vanilla C and even compiles on UNIX systems.  I call it NOBS (for NO
BackSpace).

+---------------------------------------------------------------+
|    Dave Tutelman						|
|    Physical - AT&T Bell Labs  -  Lincroft, NJ			|
|    Logical -  ...att!mtunb!dmt				|
|    Audible -  (201) 576 2442					|
+---------------------------------------------------------------+
/**********************************************************************
 *
 *	This program is a filter to fix up text for a printer that
 *	doesn't support BackSpace (NO BackSpace = NOBS).
 *	It replaces backspace sequences with carriage return sequences.
 *
 *	Dave Tutelman - September 1988
 */

/*	#define	DEBUG	*/

#include <stdio.h>

#define	LL	200	/* line length */
#define	LD	8	/* line (overstrike) depth */
#define	CR	13
#define	LF	10
#define	FF	12
#define	VT	11

char	line [LD] [LL];
int	quit=0;

main ()
{
	while ( !quit )
		do_line ();
}

/*********************************************************************/

do_line ()
{
	int	col=0;		/* current column */
	int	c;		/* current input character */
	int	eol=0;		/* end of line.. "quit" for do_line */

	clear_line ();		/* zero out the array */

	while (!eol) {		/* get characters till end of line */
		c = getchar ();
		switch (c) {
		  case EOF:
			col=0;
			eol=1;
			quit=1;
			break;

		  case FF:		/* Form Feed - done with page */
		  case LF:		/* Line Feed - done with line */
			col=0;
			eol=1;
			break;

		  case VT:		/* Vertical Tab - no more line */
			eol = 1;
			break;

		  case CR:		/* Carriage Return - back to col 0 */
			col = 0;
			break;

		  case '\t':		/* Tab - move to good col */
			col = (col / 8)*8 + 8;
			break;

		  case '\b':		/* BackSpace - back off a column */
			if (col>0) col--;
			break;

		  default:		/* put c into lines [..] array */
			insert_c (c, col);
			col ++;
			break;
		}
	}

	print_line (col);
	putchar (c);		/* use same line-ender that we got */
}

/**********************************************************************
 *	clear the line[][] array to nulls
 */

clear_line ()
{
	int	i,j;

	for (i=0; i<LD; i++)
		for (j=0; j<LL; j++)
			line [i][j] = '\0';
}

/**********************************************************************
 *	Put c into the line[..] array at column n.
 */

insert_c (c, n)
  char	c;
  int	n;
{
	int	d;

	if (n >= LL)		/* past end of line */
		return;

	for (d=0; d<LD-1; d++)		/* how deep? */
		if (line [d][n] == '\0')
			break;

	line [d][n] = c;
}

/**********************************************************************
 *	The line is done. Put to stdout from line[..] array.
 */

print_line (col)
  int	col;
{
	int	i,j;
	int	jmax;
	char	c;

	for (i=0; i<LD; i++) {
		if (i>0) {
			putchar (CR);
#ifdef DEBUG
			putchar (LF);
#endif
			col = 0;
		}

		for (jmax=LL-1; jmax>=0; jmax--)
			if (line [i][jmax])  break;
		if (jmax < 0)  break;

		for (j=col; j<=jmax; j++) {
			c = line [i] [j];
			if (c == '\0')
				c = ' ';
			putchar (c);
		}
	}
}