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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.

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 then    {check FWRITELABEL condition code}
        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. For more information about opening files, refer to chapter 5, "Opening a File".



Writing to a Magnetic Tape File

Writing User Data in ANSI Labels