dbm_clearerr, dbm_close, dbm_delete, dbm_dirfno, dbm_error,
dbm_fetch,
dbm_firstkey, dbm_nextkey, dbm_open, dbm_pagfno, dbm_store -
database access
methods
#include <ndbm.h>
int
dbm_clearerr(DBM *db);
void
dbm_close(DBM *db);
int
dbm_delete(DBM *db, datum key);
int
dbm_dirfno(DBM *db);
int
dbm_error(DBM *db);
datum
dbm_fetch(DBM *db, datum key);
datum
dbm_firstkey(DBM *db);
datum
dbm_nextkey(DBM *db);
DBM *
dbm_open(const char *file, int flags, mode_t mode);
int
dbm_pagfno(DBM *db);
int
dbm_store(DBM *db, datum key, datum content, int
store_mode);
These functions provide a ndbm-compatible interface to the
database access
methods described in db(3). Each unique record in the
database is a
key/content pair, the components of which may be any arbitrary binary data.
The key and the content data are described by the datum
data structure:
typedef struct {
void *dptr;
size_t dsize;
} datum
The dbm_open() function is used to open a database in the
file named by
file, suffixed with DBM_SUFFIX (`.db'). If necessary, the
file is created
with mode mode. Access to this file depends on the flags
parameter
(see open(2)). Read-only access may be indicated by specifying
DBM_RDONLY.
Once the database is open, dbm_fetch() is used to retrieve
the data content
associated with the key key. Similarly, dbm_store() is
used to
store the content data with the key key. When storing, the
store_mode
parameter must be one of:
DBM_INSERT Only insert new keys into the database.
Existing
key/content pairs are untouched.
DBM_REPLACE Replace any existing entry with the same
key. Any
previously stored records with the same
key are lost.
The dbm_delete() function removes the key key and its associated content
from the database.
The functions dbm_firstkey() and dbm_nextkey() are used to
iterate over
all of the records in the database. Each record will be
reached exactly
once, but in no particular order. The dbm_firstkey() function returns
the first record of the database, and thereafter
dbm_nextkey() returns
the following records. The following code traverses the entire database:
for (key = dbm_firstkey(db); key.dptr != NULL; key =
dbm_nextkey(db))
The behaviour of dbm_nextkey() is undefined if the database
is modified
after a call to dbm_firstkey().
The dbm_error() function returns the last error condition of
the
database, or 0 if no error had occurred or had been cleared.
The
dbm_clearerr() function clears the error condition of the
database.
The dbm_dirfno() function is used to find the file descriptor associated
with the directory file of an open database. Since a directory bitmap
file is not used in this implementation, this function returns the file
descriptor of the database file opened with dbm_open().
The dbm_pagfno() function is used to find the file descriptor associated
with the page file of an open database. Since a page file
is not used in
this implementation, this function is implemented as a macro
that always
returns the (undefined) value DBM_PAGFNO_NOT_AVAILABLE.
The database is closed with the dbm_close() function.
Thereafter, the db
handle is invalid.
Implementation notes [Toc] [Back]
The underlying database is a hash(3) database with a bucket
size of 4096,
a filling factor of 40, default hashing function and cache
size, and uses
the host's native byte order.
Upon successful completion, all functions that return int
return a value
of 0, otherwise a negative value is returned.
Routines that return a datum indicate errors by setting the
dptr field to
NULL.
The dbm_open() function returns NULL on error, and sets
errno appropriately.
On success, it returns a handle to the database that
should be
used as the db argument in the other functions.
The dbm_store() function returns 1 when it is called with a
flags value
of DBM_INSERT and a record with the specified key already
exists.
If an error occurs, the error can be retrieved with
dbm_error() and corresponds
to those errors described in db(3).
open(2), db(3), dbm(3), hash(3)
OpenBSD 3.6 May 13, 1998
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