HP 3000 Manuals HP 3000 Manuals
Operation
There are three basic structures used for all files: line sequential,
fixed and variable.
Line sequential is the structure of files with the line sequential
organization. It contains variable length records with trailing spaces
removed.
Fixed is the structure used by fixed format sequential and relative
files, and contains only fixed length records.
Variable is the structure of variable format sequential and relative
files, and fixed and variable format indexed sequential files. Variable
structure files can contain fixed or variable length records.
The following sections describe these file formats.
Fixed and Variable Format
The format of a file is determined by the RECMODE directive and the FD
clauses RECORDING MODE, RECORD CONTAINS n CHARACTERS and RECORD IS
VARYING. The RECORDING MODE clause overrides the RECORD clause which, in
turn, overrides the RECMODE directive. The clause RECORD CONTAINS a TO b
CHARACTERS does not affect the format.
Hence:
* RECORDING MODE IS V always creates variable format.
* RECORDING MODE IS F always creates fixed format.
* RECORD CONTAINS a TO b CHARACTERS has no effect on file format.
* RECORD IS VARYING creates variable format provided no RECORDING
MODE IS F clause is present.
* RECORD CONTAINS n CHARACTERS creates fixed format provided no
RECORDING MODE IS V clause is present.
* RECMODE"F" creates fixed format for each file where no RECORDING
MODE IS V or RECORD IS VARYING clauses are present.
* RECMODE"V" creates variable format for each file where no
RECORDING MODE IS F or RECORD CONTAINS n CHARACTERS clauses are
present.
* RECMODE"OSVS" causes the 01 definitions to determine if the file
is fixed or variable format.
Fixed Structure
Fixed structure files contain no
record or file header information. The records are all the same length,
that length being determined by the longest record defined in the File
Description (FD) in the program's FILE-SECTION.
Variable Structure
Any files containing variable length records, with the exception of line
sequential files and files destined for the printer, contain a block of
128 bytes of header information at the start of the file. In indexed
files, extra space is allocated in addition to this for blank index
pointers. Each record in the file is preceded by a 2- or 4-byte control
field. The top 4 bits of this field indicate the status of the record.
A value of 0100 in these bits means that this record is a user data
record. Any other value means that this record has either been deleted
or is used internally. The remainder of the control field contains the
length of the record.
For all files where the maximum record size is less than 4096 (excluding
the prefix), the prefix is 2 bytes long. For all other files, the prefix
is 4 bytes long. Each record always starts on the next 4 byte boundary
in the file.
You must not alter the header information or the control fields in any
way since these are maintained by this COBOL system.
Record Header Types
First 4 bits Record type
1 (0001) A system record (Idxformat 4 files only) This contains
duplicate occurrence details in the data file.
2 (0010) Deleted record (available for reuse)
3 (0011) System record
4 (0100) User data record
5 (0101) Reduced user data record (indexed files only) The 16-bit
word immediately following the data record, as indicated
by the length in the header, contains the space between
the end of the data record and the start of the next
record header
6 (0110) Pointer record (indexed files only) The first 4 bytes
following the record header contain the offset in the file
to the location of the user data record
7 (0111) User data record referenced by a Pointer record
8 (1000) Reduced user data record referenced by a Pointer record
The first record in every variable structure file is a system record
called the File Header record. This is normally 128 bytes long.
Variable structure File Header Record description:
-------------------------------------------------------------------
Offset Size Description of the field
-------------------------------------------------------------------
0 4 Length of the file header.
The first 4 bits are always set to 3 (0011 in
binary) indicating that this file header record is
a system record.
The remaining bits contain the length of the file
header record. If the maximum record length is
less than 4096 bytes, the length is 126 and is held
in the next 12 bits; otherwise it is 124 and is
held in the next 28 bits. Hence, in a file where
the maximum record length is less than 4095 bytes,
this field contains x"30 7E 00 00". Otherwise,
this field contains x"30 00 00 7C".
4 2 Database sequence number, used by add on products
from Micro Focus.
6 2 Integrity Flag. Indexed files only.
Incremented for every OPEN, decremented for every
CLOSE. If non-zero when OPEN EXCLUSIVE, indicates
that the index file is corrupt.
8 14 Creation date and time in YYMMDDHHMMSSCC format.
Indexed files only.
This date and time must be the same as the creation
date and time of index file.
22 14 Last modify date and time in YYMMDDHHMMSSCC format.
Indexed files only.
This date and time must be the same as the last
modify date and time of the index file.
36 2 Reserved. Value 62 decimal; x"00 3E".
38 1 Not used. Set to zero.
39 1 Organization.
1 = Sequential
2 = Indexed
3 = Relative
-------------------------------------------------------------------
Offset Size Description of the field
-------------------------------------------------------------------
40 1 Not used. Set to zero.
41 1 Data compression routine number.
0 = No compression
1 = CBLDC001
2-127 = Reserved for Micro Focus use
128-255 = User-defined compression routine
number
42 6 Not used. Set to zero.
43 1 File format
0 = Default
1 = C-ISAM
2 = Level II COBOL
3 = Micro Focus COBOL
4 = IDXFORMAT4
48 1 Recording mode.
0 = Fixed format
1 = Variable format
For indexed files, the Recording Mode field of the
index file takes precedence.
49 5 Not used. Set to zero.
54 2 Not used. Set to zero.
56 2 Maximum record length.
Example: with a maximum record of length 80 chars
this field will contain x"00 50".
58 2 Not used. Set to zero.
60 2 Minimum record length.
Example: with a maximum record of length 2 chars
this field will contain x"00 02".
62 46 Not used. Set to zeros.
-------------------------------------------------------------------
Offset Size Description of the field
-------------------------------------------------------------------
108 4 Version and build data for the indexed file handler
CREATING the file. Indexed files only. The
contents of this field are not fixed. Should you
wish to manipulate this field directly, you should
create an indexed file and examine the contents of
this field to determine the correct contents.
112 4 Version and build data for the indexed file handler
MODIFYING this file. Format and contents are same
as above. Indexed files only.
116 12 Not used. Set to zeros.
-------------------------------------------------------------------
The record header for each record starts on a 4-byte boundary.
Consequently, a record may be followed by up to three padding characters,
usually spaces. These padding characters are not included in the record
length.