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.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 .