HP 3000 Manuals

Accessing Files Programmer's Guide

Writing a File Label to a Labeled Tape File 
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User-defined labels are used to further identify files and may be used in
addition to the ANSI-standard labels.  User-defined labels are written on
files with the FWRITELABEL intrinsic instead of with the HPFOPEN/FOPEN
intrinsic, as is the case for writing ANSI-standard labels.[REV END]

User-defined labels for labeled tape files differ slightly from
user-defined labels for disk files, in that user-defined labels for tape
files must be 80 bytes (40 half-words) in length.  The tape label
information need not occupy all 80 bytes, however, and you can set unused
portions of the space equal to blanks.

In order to write a user-defined header label, the FWRITELABEL intrinsic
must be called before the first FWRITE to the file.  MPE/iX does,
however, write user-defined trailer labels if FWRITELABEL is called after
the first FWRITE.


NOTE  User-defined labels may not be written on unlabeled magnetic tape
      files.


Example 8-8 is an HP Pascal/iX code segment that writes a user-label 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 8-8.  Writing a User-Label to a Labeled Magnetic Tape File. 

             :
     var
        counter      : integer;         {Initialize counter                }
        label_length : shortint;        {FWRITELABEL length parm           }
        user_label   : packed array [1..80] of char;
             :
        label_length := 40;             {40 half-words required length     }
        for counter  := 1 to 80 do      {Loop to fill array with           }
           user_label [counter] := ' '; {ASCII blanks.                     }
        user_label   := 'tape01 user header label no. 1'; {Overwrite first }
                                                 {30 bytes with label name }

     FWRITELABEL (labeled_tape_file,    {Required parameter                }
                  user_label,           {Required parameter                }
                  label_length          {Optional parameter                }
                 );

     if ccode = CCL or CCG              {check FWRITELABEL condition code  }
        then handle_file_error (labeled_tape_file);
                :

If ccode indicates that the FWRITELABEL intrinsic encountered an
error condition (either CCL or CCG), an error handling procedure
handle_file_error is invoked.  For more information about FWRITELABEL
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".

MPE/iX 5.0 Documentation