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FPOINT
INTRINSIC NUMBER 6
Sets the chronological (and logical) record pointer for a KSAM file.
IV DV
FPOINT(filenum,recnum);
The FPOINT intrinsic sets the chronological record pointer for a KSAM
disc file. The file may contain either fixed-length or variable-length
records. When the next FREADC request is issued for this file, the
record to which FPOINT positioned the pointer is read. Note that this
intrinsic positions the logical record pointer as well as the
chronological pointer.
PARAMETERS
filenum integer by value (required)
A word identifier supplying the file number of the file
on which the pointer is to be set.
recnum double by value (required)
A positive double integer representing the record number
of a fixedlength file or the word pointer to a
variable-length file. Word numbering always starts with
word 0, whereas record numbering starts with 0 or 1
depending on how the file was created. In either case,
the number is in terms of the chronological
(consecutive) order in which the data file records were
written. It has no relation to the logical record
pointer that is based on key values.
CONDITION CODES
CCE Request granted.
CCG Request denied. The chronological record pointer
position is unchanged. Positioning was requested at a
point beyond the physical end-of-file.
CCL Request denied. The chronological record pointer
position is unchanged because of one of the following:
Invalid filenum parameter.
recnum parameter specified a record marked for
deletion.
A key value for specified record not found in key
file.
SPECIAL CONSIDERATIONS
Split stack calls permitted.
USING FPOINT
The FPOINT intrinsic is generally used prior to an FREADC intrinsic in
order to read a record without reference to the key file. FPOINT sets
the chronological record pointer to the position in the file specified by
recnum. A subsequent FREADC reads the record (or portion of a record) to
which the pointer is positioned. It then sets the pointer to the next
record that was written to the file in chronological order,
For example, in order to read the 39th record written to the file
identified by FILENUM:
FPOINT(FILNUM,39D); <<set pointer>>
FREADC(FILNUM,BUFFER,COUNT); <<read record>>
Following execution of FREADC, the contents of the 39th record are
transferred to the array BUFFER and the chronological pointer remains
positioned at record 39. A flag is set so that the next call to FREADC
moves the pointer forward to the beginning of record 40, the next record
in chronological order.
Note that the combination of FPOINT followed by an FREADC intrinsic is
identical in effect to the FREADDIR intrinsic that positions to a
chronological record number and then reads that record. The FGETINFO
intrinsic can be used to recover the chronological record number of the
record most recently accessed. (Refer to FGETINFO and FREADDIR for more
information on accessing records by chronological record number.)
Since the FPOINT intrinsic positions the logical pointer as well as the
chronological pointer, it can be used prior to an FUPDATE or FREAD
intrinsic to identify the record to be updated or read. FPOINT sets the
logical record pointer to a key in the key file that points to the record
it located by record number. The key is by default the primary key for
that record, though an alternate key is used if such a key was selected
by a prior call to FFINDBYKEY or FREADBYKEY.
SHARED ACCESS. When you use FPOINT to position the chronological pointer
in a shared access environment, you must lock the file with a call to
FLOCK before calling FPOINT. You should leave the file locked until you
have completed any calls that read or update the file in chronological
sequence, and then call FUNLOCK to unlock the file for the other users.
This insures that the pointer is not moved by other users between the
pointer-independent procedure FPOINT and any subsequent pointer-dependent
procedure. (Refer to Table 4-2 for a list of the pointer-independent and
pointer-dependent procedures.)