NDBM(3) BSD Programmer's Manual NDBM(3)
dbm_clearerr, dbm_close, dbm_delete, dbm_dirfno, dbm_error, dbm_fetch,
dbm_firstkey, dbm_nextkey, dbm_open, dbm_pagfno, dbm_rdonly, 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_rdonly(DBM *db);
int
dbm_store(DBM *db, datum key, datum content, int store_mode);
These functions provide a ndbm-compatible interface to the database ac-
cess 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 struc-
ture:
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. The
dbm_rdonly() function may be used to determine if a database is opened
for read-only access.
Once the database is open, dbm_fetch() is used to retrieve the data con-
tent 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 pre-
viously 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 data-
base, 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.
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 appropri-
ately. 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)
MirBSD #10-current May 13, 1998 1