XABFHC

   The file header characteristic XAB (XABFHC) contains file header
   information that is output by the Open service and the Display
   service. The Create service can output information in this XAB
   when it opens an existing file through use of the Create-if
   option.

   The only input field is the longest record length (XAB$W_LRL)
   field. The Create service uses this field when it creates a
   sequential file that does not use a fixed-length record format.

   Note that, for unshared sequential files or sequential files
   shared using the FAB$V_UPI option, the values in the end-of-
   file block (XAB$L_EBK), first free byte in the end-of-file
   block (XAB$W_FFB), and longest record length (XAB$W_LRL) fields
   correspond to the values at the time of the last Close or Flush
   service.

   The following table lists the symbolic offset, the size in bytes,
   and a brief description of each field.

   Offset        Size    Description

   XAB$B_ATR     1       Record attributes; equivalent to FAB$B_RAT
   XAB$B_BKZ     1       Bucket size; equivalent to FAB$B_BKS
   XAB$B_BLN     1       Block length
   XAB$B_COD     1       Type code
   XAB$W_DXQ     2       Default file extension quantity; equivalent
                         to FAB$W_DEQ
   XAB$L_EBK     4       End-of-file block
   XAB$W_FFB     2       First free byte in the end-of-file block
   XAB$W_GBC     2       Default global buffer count
   XAB$L_HBK     4       Highest virtual block in the file;
                         equivalent to FAB$L_ALQ
   XAB$B_HSZ     1       Fixed-length control header size;
                         equivalent to FAB$B_FSZ
   XAB$W_LRL     2       Longest record length
   XAB$W_MRZ     2       Maximum record size; equivalent to FAB$W_
                         MRS
   XAB$L_NXT     4       Next XAB address
   XAB$B_RFO     1       File organization and record format;
                         combines FAB$B_RFM and FAB$B_ORG
   XAB$L_SBN     4       Starting logical block number for the file
                         if it is contiguous; otherwise this field
                         is 0
   XAB$W_        2       Version limit for the file
   VERLIMIT