topen.3f

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)topen.3f	8.1	9/11/90
.TH topen 3f VAX "" Unsupported
.SH Name
topen, tclose, tread, twrite, trewin, tskipf, tstate \- f77 tape I/O
.SH Syntax
.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
.NXR "topen subroutine (FORTRAN)"
.NXR "tclose subroutine (FORTRAN)"
.NXR "tread subroutine (FORTRAN)"
.NXR "twrite subroutine (FORTRAN)"
.NXR "trewind subroutine (FORTRAN)"
.NXR "tskipf subroutine (FORTRAN)"
.NXR "tstate subroutine (FORTRAN)"
.NXR "f77 compiler" "magnetic tape devices and"
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
It should be noted that these functions return integers and
should be declared in the user program before using them.  The
default function return value for the f77 compiler is float.
The failure to declare these functions will produce improper
results.
.PP
The
.PN topen
function
associates a device name with a
.IR tlu .
The
.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
.PN trewin
below.
The
.PN topen
function
does not move the tape.
The normal returned value is 0.
If the value of the function is negative, 
an error has occurred.  
See 
.MS perror 3f
for details.
.PP
The
.PN tclose
function 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
The
.PN tread
function reads the next physical record from tape to
.IR buffer .
The
.I buffer
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
The
.PN twrite
function writes a physical record to tape from
.IR buffer .
The physical record length will be the size of
.IR buffer .
The
.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
The
.PN trewin
function
rewinds the tape associated with
.I tlu
to the beginning of the first data file.
If the tape is a labeled tape
then the label is skipped over after rewinding.
For further information, see
.PN topen
above.
The normal returned value is 0.
A negative value indicates an error.
.PP
The
.PN tskipf
function 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, the
.PN tstate
function
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.
For further details, see 
.MS tu 4 .
.SH Files
.ie \nM /usr/ucb/lib/libU77.a
.el /usr/lib/libU77.a
.SH See Also
fseek(3f), perror(3f), tu(4)