The following discussion pertains to writing
data to two different types of magnetic tape files.
unlabeled magnetic tape files
labeled magnetic tape files
Unless you specifically create and open a labeled magnetic tape file, the file
system opens an unlabeled magnetic tape file when you specify a tape drive
using either the device name option or device class option of HPFOPEN/FOPEN.
For more information about opening both unlabeled and labeled magnetic tape
files, refer to chapter 5, "Opening a File".
When you are writing records to an unlabeled magnetic tape file, you must take
into consideration characteristics of magnetic tape that do not apply to files
on other devices. For example, if a user program attempts to write over or
beyond the physical EOT marker, the FWRITE intrinsic returns an error condition
code (CCL). The actual data is written to the tape, and a call to FCHECK
reveals a file error indicating END-OF-TAPE. All writes to the tape after the
EOT tape marker has been crossed transfer the data successfully, but return a
CCL condition code until the tape crosses the EOT marker again in the reverse
direction (rewind or backspace). For more information about magnetic tape
considerations, refer to chapter 7, "Record Selection and Data Transfer".
Writing records to a labeled tape file differs slightly from writing to an
unlabeled tape file. If the magnetic tape is unlabeled and a user program
attempts to write over or beyond the physical EOT marker, the FWRITE intrinsic
returns an error condition code (CCL). The actual data has been written to the
tape, and a call to FCHECK reveals a file error indicating END-OF-TAPE. All
writes to the tape after the EOT tape marker has been crossed transfer the data
successfully, but return a CCL condition code until the tape crosses the EOT
marker again in the reverse direction (rewind or backward).
If the magnetic tape is labeled, a CCL condition code is not returned when the
tape passes the EOT marker. Attempts to write to the tape after the EOT marker
is encountered cause end-of-volume (EOV) labels to be written. A message then
is printed on the operator's console requesting another reel of tape to be
mounted.
The following headings provide examples of file system intrinsic calls that
illustrate:
writing to an unlabeled magnetic tape file
writing to a labeled magnetic tape file
writing a user-defined file label on a labeled tape file
Writing to an unlabeled magnetic tape file |
 |
Example 8-6 is an HP Pascal/iX code
segment that writes user-supplied data to the unlabeled magnetic tape file
opened in example 5-5. For information about the HPFOPEN call that returns the
file number in the variable unlabeled_tape_file, refer to example 5-5.
Example 8-6. Writing to an Unlabeled Magnetic Tape File
.
.
.
var
control_code : 0..65535; {Declare FWRITE parm. }
record_length: shortint; {Declare FWRITE parm }
file_record : record_type; {Record to be written to file; }
{record_type is 256-byte }
{fixed-length record. }
.
.
.
record_length:= -256; {Number of bytes in record. }
control_code := 0; {Default specified }
FWRITE ( unlabeled_tape_file, {HPFOPEN returned file number. }
file_record {Record to be passed }
record_length {Size of file_record. }
control_code {Required, but ignored. }
);
if ccode = CCL {check FWRITE condition code }
then handle_file_error (labeled_tape_file);
.
.
.
|
If the FWRITE intrinsic encounters an error condition (CCL), an error-handling
procedure, handle_file_error, is invoked. FWRITE returns a CCG condition code if
the EOF is reached. For details concerning FWRITE intrinsic parameters, refer
to the MPE/iX Intrinsics Reference Manual (32650-90028).
Writing to a labeled magnetic tape file |
|
Example 8-7 is an HP Pascal/iX code
segment that writes user-supplied data to the labeled magnetic tape file opened
in Example 5-6. For information about the HPFOPEN call that returns the file
number in the variable labeled_tape_file, refer to example 5-6.
Example 8-7. Writing to a Labeled Magnetic Tape File
.
.
.
var
control_code : 0..65535; {Declare FWRITE parm. }
record_length: shortint; {Declare FWRITE parm }
file_record : record_type; {Record to be written to file; }
{record_type is 256-byte }
{fixed-length record. }
.
.
.
record_length:= -256; {Number of bytes in record. }
control_code := 0; {Default specified }
FWRITE ( labeled_tape_file, {HPFOPEN returned file number. }
file_record {Record to be passed }
record_length {Size of file_record. }
control_code {Required, but ignored. }
);
if ccode = CCL {check FWRITE condition code }
then handle_file_error (labeled_tape_file);
.
.
.
|
If the FWRITE intrinsic encounters an error condition (CCL), an error handling
procedure handle_file_error is invoked. FWRITE returns a CCG condition code if
the EOF is reached. For more information about FWRITE intrinsic parameters,
refer to the MPE/iX Intrinsics Reference Manual (32650-90028). For more
information about opening files, refer to chapter 5, "Opening a File".
