.TH TOPEN 3F
.UC
.SH NAME
topen, tclose, tread, twrite, trewin, tskipf, tstate \- f77 tape I/O
.SH SYNOPSIS
.B integer function topen 
(tlu, devnam, label)
.br
.B integer
tlu
.br
.B character*(*)
devnam
.br
.B logical
label
.sp 1
.B integer function tclose
(tlu)
.br
.B integer
tlu
.sp 1
.B integer function tread
(tlu, buffer)
.br
.B integer
tlu
.br
.B character*(*)
buffer
.sp 1
.B integer function twrite
(tlu, buffer)
.br
.B integer
tlu
.br
.B character*(*)
buffer
.sp 1
.B integer function trewin
(tlu)
.br
.B integer
tlu
.sp 1
.B integer function tskipf
(tlu, nfiles, nrecs)
.br
.B integer
tlu, nfiles, nrecs
.sp 1
.B integer function tstate
(tlu, fileno, recno, errf, eoff, eotf, tcsr)
.br
.B integer
tlu, fileno, recno, tcsr
.br
.B logical
errf, eoff, eotf
.SH DESCRIPTION
These functions provide a simple interface between f77 and magnetic
tape devices.
A ``tape logical unit'',
.IR tlu ,
is ``topen''ed in much the same way as a normal f77 logical unit
is ``open''ed.
All other operations are performed via the
.IR tlu .
The
.I tlu
has no relationship at all to any normal f77 logical unit.
.PP
.I Topen
associates a device name with a
.IR tlu .
.I Tlu
must be in the range 0 to 3.
The logical argument
.I label
should indicate whether the tape includes a tape label.
This is used by
.I trewin
below.
.I Topen
does not move the tape.
The normal returned value is 0.
If the value of the function is negative, an error has occured.
See
.IR perror (3f)
for details.
.PP
.I Tclose
closes the tape device channel and removes its association with
.IR tlu .
The normal returned value is 0.
A negative value indicates an error.
.PP
.I Tread
reads the next physical record from tape to
.IR buffer .
.I Buffer
.B must
be of type
.BR character .
The size of
.I buffer
should be large enough to hold the largest physical record to be read.
The actual number of bytes read will be returned as the value of the
function.
If the value is 0, the end-of-file has been detected.
A negative value indicates an error.
.PP
.I Twrite
writes a physical record to tape from
.IR buffer .
The physical record length will be the size of
.IR buffer .
.I Buffer
.B must
be of type
.BR character .
The number of bytes written will be returned.
A value of 0 or negative indicates an error.
.PP
.I Trewin
rewinds the tape associated with
.I tlu
to the beginning of the first data file.
If the tape is a labelled tape
(see
.I topen
above)
then the label is skipped over after rewinding.
The normal returned value is 0.
A negative value indicates an error.
.PP
.I Tskipf
allows the user to skip over files and/or records.
First,
.I nfiles
end-of-file marks are skipped. If the current file is at
EOF, this counts as 1 file to skip.
(Note: This is the way to reset the EOF status for a
.IR tlu .)
Next,
.I nrecs
physical records are skipped over.
The normal returned value is 0.
A negative value indicates an error.
.PP
Finally,
.I tstate
allows the user to determine the logical state of the tape I/O channel
and to see the tape drive control status register.
The values of
.I fileno
and
.I recno
will be returned and indicate the current file and record number.
The logical values
.IR errf ,
.IR eoff ,
and
.I eotf
indicate an error has occurred, the current file is at EOF,
or the tape has reached logical end-of-tape.
End-of-tape (EOT) is indicated by an empty file, often
referred to as a double EOF mark.
It is not allowed to read past EOT although it is allowed to write.
The value of
.I tcsr
will reflect the tape drive control status register.
.SH FILES
.ie \nM /usr/ucb/lib/libU77.a
.el /usr/lib/libU77.a
.SH "SEE ALSO"
rewind(1), perror(3f), mt(4)