.\" Copyright (c) 1999 Tim Singletary
.\" No copyright is claimed.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd April 2, 2022
.Dt DBM 3
.Os
.Sh NAME
.Nm dbm_clearerr ,
.Nm dbm_close ,
.Nm dbm_delete ,
.Nm dbm_dirfno ,
.Nm dbm_error ,
.Nm dbm_fetch ,
.Nm dbm_firstkey ,
.Nm dbm_nextkey ,
.Nm dbm_open ,
.Nm dbm_store
.Nd database access functions
.Sh SYNOPSIS
.In fcntl.h
.In ndbm.h
.Ft DBM *
.Fn dbm_open "const char *base" "int flags" "mode_t mode"
.Ft void
.Fn dbm_close "DBM *db"
.Ft int
.Fn dbm_store "DBM *db" "datum key" "datum data" "int flags"
.Ft datum
.Fn dbm_fetch "DBM *db" "datum key"
.Ft int
.Fn dbm_delete "DBM *db" "datum key"
.Ft datum
.Fn dbm_firstkey "DBM *db"
.Ft datum
.Fn dbm_nextkey "DBM *db"
.Ft int
.Fn dbm_error "DBM *db"
.Ft int
.Fn dbm_clearerr "DBM *db"
.Ft int
.Fn dbm_dirfno "DBM *db"
.Sh DESCRIPTION
Database access functions.
These functions are implemented using
.Xr dbopen 3
with a
.Xr hash 3
database.
.Pp
.Vt datum
is declared in
.In ndbm.h :
.Bd -literal
typedef struct {
	void *dptr;
	int dsize;
} datum;
.Ed
.Pp
The
.Fn dbm_open base flags mode
function
opens or creates a database.
The
.Fa base
argument
is the basename of the file containing
the database; the actual database has a
.Pa .db
suffix.
I.e., if
.Fa base
is
.Qq Li /home/me/mystuff
then the actual database is in the file
.Pa /home/me/mystuff.db .
The
.Fa flags
and
.Fa mode
arguments
are passed to
.Xr open 2 .
.Pq Dv O_RDWR | O_CREAT
is a typical value for
.Fa flags ;
.Li 0660
is a typical value for
.Fa mode .
.Dv O_WRONLY
is not allowed in
.Fa flags .
The pointer returned by
.Fn dbm_open
identifies the database and is the
.Fa db
argument to the other functions.
The
.Fn dbm_open
function
returns
.Dv NULL
and sets
.Va errno
if there were any errors.
.Pp
The
.Fn dbm_close db
function
closes the database.
.Pp
The
.Fn dbm_store db key data flags
function
inserts or replaces an entry in the database.
The
.Fa flags
argument
is either
.Dv DBM_INSERT
or
.Dv DBM_REPLACE .
If
.Fa flags
is
.Dv DBM_INSERT
and the database already contains an entry for
.Fa key ,
that entry is not replaced.
Otherwise the entry is replaced or inserted.
The
.Fn dbm_store
function
normally returns zero but returns 1 if the entry could not be
inserted (because
.Fa flags
is
.Dv DBM_INSERT ,
and an entry with
.Fa key
already exists) or returns -1 and sets
.Va errno
if there were any errors.
.Pp
The
.Fn dbm_fetch db key
function
returns
.Dv NULL
or the
.Fa data
corresponding to
.Fa key .
.Pp
The
.Fn dbm_delete db key
function
deletes the entry for
.Fa key .
The
.Fn dbm_delete
function
normally returns zero or returns -1 and sets
.Va errno
if there were any errors.
.Pp
The
.Fn dbm_firstkey db
function
returns the first key in the database.
The
.Fn dbm_nextkey db
function
returns subsequent keys.
The
.Fn db_firstkey
function
must be called before
.Fn dbm_nextkey .
The order in which keys are returned is unspecified and may appear
random.
The
.Fn dbm_nextkey
function
returns
.Dv NULL
after all keys have been returned.
.Pp
The
.Fn dbm_error db
function
returns the
.Va errno
value of the most recent error.
The
.Fn dbm_clearerr db
function
resets this value to 0 and returns 0.
.Pp
The
.Fn dbm_dirfno db
function
returns the file descriptor to the database.
.Sh SEE ALSO
.Xr open 2 ,
.Xr dbopen 3 ,
.Xr hash 3
.Sh STANDARDS
These functions (except
.Fn dbm_dirfno )
are included in the
.St -susv2 .
.Sh HISTORY
The functions
.Fn dbminit ,
.Fn fetch ,
.Fn store ,
.Fn delete ,
.Fn firstkey ,
and
.Fn nextkey
first appeared in
.At v7 .