The first record in every variable structure file is a system record called
the file header. This is normally 128 bytes in length and takes the following
form:
| Offset |
Size |
Description |
| 0 |
4 |
Length of the file header. The first 4 bits are always set to 3 (0011 in
binary) indicating that this is a system record. The remaining bits contain
the length of the file header record. If the maximum record length is less
than 4095 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. |
| 6 |
2 |
Integrity flag. Indexed files only. If this is non-zero when the header is
read, it indicates that the file is corrupt. |
| 8 |
14 |
Creation date and time in YYMMDDHHMMSSCC format. Indexed files only. |
| 22 |
14 |
Reserved. |
| 36 |
2 |
Reserved. Value 62 decimal; x"00 3E". |
| 38 |
1 |
Not used. Set to zeros. |
| 39 |
1 |
Organization:
| 1 |
Sequential |
| 2 |
Indexed |
| 3 |
Relative | |
| 40 |
1 |
Not used. Set to zeros. |
| 41 |
1 |
Data compression routine number:
| 0 |
No compression |
| 1 |
CBLDC001 |
| 2-127 |
Reserved for internal use |
| 128-255 |
User-defined compression routine number | |
| 42 |
1 |
Not used. Set to zeros. |
| 43 |
1 |
Indexed files only - type of indexed file. See the topic Types of Indexed
File. |
| 44 |
4 |
Reserved. |
| 48 |
1 |
Recording mode:
| 0 |
Fixed format |
| 1 |
Variable format |
For indexed files, the recording mode field of the .idx file takes precedence. |
| 49 |
5 |
Not used. Set to zeros. |
| 54 |
4 |
Maximum record length. Example: with a maximum record of length 80 characters,
this field will contain x"00 00 00 50". |
| 58 |
4 |
Minimum record length. Example: with a minimum record length of 2 characters,
this field will contain x"00 00 00 02". |
| 62 |
46 |
Not used. Set to zeros. |
| 108 |
4 |
Version and build data for the indexed file handler creating the file. Indexed
files only. |
| 112 |
16 |
Not used. Set to zeros. |