RECNO(3) | Library Functions Manual | RECNO(3) |
recno
— record
number database access method
#include
<sys/types.h>
#include <db.h>
The routine
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; u_char 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.recno
access method stores the in-memory
copies of its records in a btree. This value is the size (in bytes) of the
pages used for nodes in that tree. If psize is 0 (no
page size is specified) a page size is chosen based on the underlying file
system I/O block size. See btree(3)
for more information.recno
access method stores the in-memory
copies of its records in a btree. If bfname is
non-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.
The 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
]btree(3), dbopen(3), hash(3), mpool(3)
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.
Only big and little endian byte order is supported.
August 18, 1994 | macOS 14.6 |