| Chapter 25 |
The dbm library: access to NDBM databases |
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The dbm library provides access to NDBM databases under Unix.
NDBM databases maintain key/data associations, where both the key and
the data are arbitrary strings. They support fairly large databases
(several gigabytes) and can retrieve a keyed item in one or two file
system accesses. Refer to the Unix manual pages for more information.
Unix:
Programs that use the dbm library must be linked as follows:
nmlc other options dbm.cma other files
Windows:
This library is not available.
| 25.1 |
Module Dbm: interface to the NDBM database |
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type t
The type of file descriptors opened on NDBM databases.
type open_flag =
Dbm_rdonly | Dbm_wronly | Dbm_rdwr | Dbm_create
Flags for opening a database (see opendbm).
exception Dbm_error of string
Raised by the following functions when an error is encountered.
val opendbm : string -> mode:open_flag list -> perm:int -> t
Open a descriptor on an NDBM database. The first argument is
the name of the database (without the .dir and .pag suffixes).
The second argument is a list of flags: Dbm_rdonly opens
the database for reading only, Dbm_wronly for writing only,
Dbm_rdwr for reading and writing; Dbm_create causes the
database to be created if it does not already exist.
The third argument is the permissions to give to the database
files, if the database is created.
val close : t -> unit
Close the given descriptor.
val find : t -> string -> string
find db key returns the data associated with the given
key in the database opened for the descriptor db.
Raise Not_found if the key has no associated data.
val add : t -> key:string -> data:string -> unit
add db key data inserts the pair (key, data) in
the database db. If the database already contains data
associated with key, raise Dbm_error "Entry already exists".
val replace : t -> key:string -> data:string -> unit
replace db key data inserts the pair (key, data) in
the database db. If the database already contains data
associated with key, that data is discarded and silently
replaced by the new data.
val remove : t -> string -> unit
remove db key data removes the data associated with key
in db. If key has no associated data, raise
Dbm_error "dbm_delete".
val firstkey : t -> string
val nextkey : t -> string
Enumerate all keys in the given database, in an unspecified order.
firstkey db returns the first key, and repeated calls
to nextkey db return the remaining keys. Not_found is raised
when all keys have been enumerated.
val iter : f:(key:string -> data:string -> 'a) -> t -> unit
iter f db applies f to each (key, data) pair in
the database db. f receives key as first argument
and data as second argument.