HASH(3) | Library Functions Manual | HASH(3) |
hash
— hash
database access method
#include
<sys/types.h>
#include <db.h>
The dbopen
() routine is the library
interface to database files. One of the supported file formats is hash
files. The general description of the database access methods is in
dbopen(3). This manual page describes
only the hash specific information.
The hash data structure is an extensible, dynamic hashing scheme.
The access method specific data structure provided to
dbopen
() is defined in the
<db.h>
include file as
follows:
typedef struct { unsigned int bsize; unsigned int ffactor; unsigned int nelem; unsigned int cachesize; u_int32_t (*hash)(const void *, size_t); int lorder; } HASHINFO;
The elements of this structure are as follows:
If the file already exists (and the
O_TRUNC
flag is not specified), the values specified
for the parameters bsize,
ffactor, lorder and
nelem are ignored and the values specified when the
tree was created are used.
If a hash function is specified,
hash_open
() will attempt to determine if the hash
function specified is the same as the one with which the database was
created, and will fail if it is not.
Backward compatible interfaces to the routines described in ndbm(3) are provided, although these interfaces are not compatible with previous file formats.
The hash
access method routines may fail
and set errno for any of the errors specified for the
library routine dbopen(3).
Per-Ake Larson, Dynamic Hash Tables, Communications of the ACM, April 1988.
Margo Seltzer, A New Hash Package for UNIX, USENIX Proceedings, Winter 1991.
Only big and little endian byte order is supported.
May 9, 2016 | OpenBSD-current |