.help zfiolp May84 "System Interface"
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NAME
zfiolp -- line printer driver
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SYNOPSIS
.nf
zopnlp (osfn, mode, chan)		# open line printer
zclslp (chan, status)			# close line printer
zardlp (chan, buf, maxbytes, loffset)	# asynchronous read
zawrlp (chan, buf,   nbytes, loffset)	# asynchronous write
zawtlp (chan, status)			# wait for transfer
zsttlp (chan, param, lvalue)		# get file/device status

packed	char osfn[]
char	buf[]
int	mode, chan, maxbytes, nbytes, param, status
long	loffset, lvalue
.fi
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DESCRIPTION
The line printer devices are interfaced as binary files.  Except where noted
herein, the line printer driver is functionally equivalent to the driver for
an ordinary streaming binary file.

A line printer device is opened with \fBzopnlp\fR and closed with \fBzclslp\fR.
The name of the device to be opened is given by \fIosfn\fR and is host system
dependent.  The names of the printer devices recognized by \fBzopnlp\fR must
agree with those in the CL environment list and in the printer capability file
\fBdev$printcap\fR.  Only the APPEND and WRITE_ONLY modes are supported by
most printer devices.  Depending on the location and characteristics of the
device, \fBzopnlp\fR may or may not open the device directly.  Often a
binary spoolfile is opened instead, and the spoolfile is (asynchronously)
disposed of to the physical device when \fBzclspr\fR is called.

Binary data is copied to the printer device without modification, hence all
control functions (including newline) must have been fully translated into
device dependent control sequences by the time \fBzawrlp\fR is called to
output the data to the device.  Either character data or binary bitmap data
(graphics) may be transmitted to a printer device.
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NOTES
If the printer device is very fast it will not be desirable to spool printer
output when printing large text files due to the additional expense of writing
a large spoolfile.  A better approach is to write directly to the device if
it is available, spooling only if the device is already in use at \fBzopnlp\fR
time.  A second virtual device can be defined which writes to the same
physical device but which always spools the output.  If the line printer
device is shared in a local area network it may be necessary to spool the
output and copy the spoolfile to a remote host for disposal to the printer.
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SEE ALSO
zfiobf, lpopen, dev$printcap, manual pages for the binary file driver
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