RECNO(3) | Library Functions Manual | RECNO(3) |
recno
—
#include <sys/types.h>
#include <db.h>
dbopen
() is the library interface to
database files. One of the supported file formats is record number files. The
general description of the database access methods is in
dbopen(3), this manual page
describes only the recno specific information.
The record number data structure is either variable or fixed-length records stored in a flat-file format, accessed by the logical record number. The existence of record number five implies the existence of records one through four, and the deletion of record number one causes record number five to be renumbered to record number four, as well as the cursor, if positioned after record number one, to shift down one record.
The recno access method specific data structure provided to
dbopen
() is defined in the
<db.h>
include file as
follows:
typedef struct { u_long flags; u_int cachesize; u_int psize; int lorder; size_t reclen; uint8_t bval; char *bfname; } RECNOINFO;
The elements of this structure are defined as follows:
R_FIXEDLEN
R_NOKEY
dbopen
(), the
sequential record retrieval fills in both the caller's key and data
structures. If the R_NOKEY
flag is specified,
the cursor routines are not required to fill in the key structure.
This permits applications to retrieve records at the end of files
without reading all of the intervening records.R_SNAPSHOT
dbopen
() is called, instead of permitting any
unmodified records to be read from the original file.NULL
, it specifies the
name of the btree file, as if specified as the file name for a
dbopen
() of a btree file.The data part of the key/data pair used by the recno access method
is the same as other access methods. The key is different. The
data field of the key should be a pointer to a memory
location of type recno_t, as defined in the
<db.h>
include file. This
type is normally the largest unsigned integral type available to the
implementation. The size field of the key should be
the size of that type.
Because there can be no meta-data associated with the underlying recno access method files, any changes made to the default values (e.g., fixed record length or byte separator value) must be explicitly specified each time the file is opened.
In the interface specified by dbopen
(),
using the put interface to create a new record will
cause the creation of multiple, empty records if the record number is more
than one greater than the largest record currently in the database.
recno
access method routines may fail and set
errno for any of the errors specified for the library
routine dbopen(3) or the
following:
EINVAL
Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman, and Nadene Lynn, Document Processing in a Relational Database System, Memorandum No. UCB/ERL M82/32, May 1982.
April 17, 2003 | NetBSD 9.0 |