dbm_clearerr(3)                                         dbm_clearerr(3)

  dbm_clearerr()

  NAME

    dbm_clearerr, dbm_close, dbm_delete, dbm_error, dbm_fetch, dbm_firstkey,
    dbm_nextkey, dbm_open, dbm_store - database functions

  SYNOPSIS

    #include 

    int dbm_clearerr(DBM *db);
    void dbm_close(DBM *db);
    int dbm_delete(DBM *db, datum key);
    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 open_flags, mode_t file_mode);
    int dbm_store(DBM *db, datum key, datum content, int store_mode);

  DESCRIPTION

    These functions create, access and modify a database.

    A datum consists of at least two members, dptr and dsize. The dptr member
    points to an object that is dsize bytes in length. Arbitrary binary data,
    as well as character strings, may be stored in the object pointed to by
    dptr.

    The database is stored in two files. One file is a directory containing a
    bit map of keys and has .dir as its suffix. The second file contains all
    data and has .pag as its suffix.

    The dbm_open(3) function opens a database. The file argument to the
    function is the pathname of the database. The open_flags argument has the
    same meaning as the flags argument of open(2) except that a database
    opened for write-only access opens the files for read and write access and
    the behaviour of the O_APPEND flag is unspecified. The file_mode argument
    has the same meaning as the third argument of open(2).

    The dbm_close(3) function closes a database. The argument db must be a
    pointer to a dbm structure that has been returned from a call to
    dbm_open(3).

    The dbm_fetch(3) function reads a record from a database. The argument db
    is a pointer to a database structure that has been returned from a call to
    dbm_open(3). The argument key is a datum that has been initialised by the
    application program to the value of the key that matches the key of the
    record the program is fetching.

    The dbm_store(3) function writes a record to a database. The argument db
    is a pointer to a database structure that has been returned from a call to
    dbm_open(3). The argument key is a datum that has been initialised by the
    application program to the value of the key that identifies (for
    subsequent reading, writing or deleting) the record the program is
    writing. The argument content is a datum that has been initialised by the
    application program to the value of the record the program is writing. The
    argument store_mode controls whether dbm_store(3) replaces any pre-
    existing record that has the same key that is specified by the key
    argument. The application program must set store_mode to either DBM_INSERT
    or DBM_REPLACE. If the database contains a record that matches the key
    argument and store_mode is DBM_REPLACE, the existing record is replaced
    with the new record. If the database contains a record that matches the
    key argument and store_mode is DBM_INSERT, the existing record is not
    replaced with the new record. If the database does not contain a record
    that matches the key argument and store_mode is either DBM_INSERT or
    DBM_REPLACE, the new record is inserted in the database.

    The sum of the sizes of a key/content pair must not exceed the internal
    block size. Moreover, all key/content pairs that hash together must fit on
    a single block. The dbm_store(3) function returns an error in the event
    that a disk block fills with inseparable data.

    The dbm_delete(3) function deletes a record and its key from the database.
    The argument db is a pointer to a database structure that has been
    returned from a call to dbm_open(3). The argument key is a datum that has
    been initialised by the application program to the value of the key that
    identifies the record the program is deleting.

    The dbm_firstkey(3) function returns the first key in the database. The
    argument db is a pointer to a database structure that has been returned
    from a call to dbm_open(3).

    The dbm_nextkey(3) function returns the next key in the database. The
    argument db is a pointer to a database structure that has been returned
    from a call to dbm_open(3). The dbm_firstkey(3) function must be called
    before calling dbm_nextkey(3). Subsequent calls to dbm_nextkey(3) return
    the next key until all of the keys in the database have been returned.

    The dbm_error(3) function returns the error condition of the database. The
    argument db is a pointer to a database structure that has been returned
    from a call to dbm_open(3).

    The dbm_clearerr(3) function clears the error condition of the database.
    The argument db is a pointer to a database structure that has been
    returned from a call to dbm_open(3).

    These database functions support key/content pairs of at least 1023 bytes.

    The dptr pointers returned by these functions may point into static
    storage that may be changed by subsequent calls.

    These interfaces need not be reentrant.

  RETURN VALUE

    The dbm_store(3) and dbm_delete(3) functions return 0 when they succeed
    and a negative value when they fail.

    The dbm_store(3) function returns 1 if it is called with a flags value of
    DBM_INSERT and the function finds an existing record with the same key.

    The dbm_error(3) function returns 0 if the error condition is not set and
    returns a non-zero value if the error condition is set.

    The return value of dbm_clearerr(3) is unspecified.

    The dbm_firstkey(3) and dbm_nextkey(3) functions return a key datum. When
    the end of the database is reached, the dptr member of the key is a null
    pointer. If an error is detected, the dptr member of the key is a null
    pointer and the error condition of the database is set.

    The dbm_fetch(3) function returns a content datum. If no record in the
    database matches the key or if an error condition has been detected in the
    database, the dptr member of the content is a null pointer.

    The dbm_open(3) function returns a pointer to a database structure. If an
    error is detected during the operation, dbm_open(3) returns a (DBM *)0.

  ERRORS

    No errors are defined.

  EXAMPLES

    None.

  APPLICATION USAGE

    The following code can be used to traverse the database:

    for(key = dbm_firstkey(db); key.dptr != NULL; key = dbm_nextkey(db))

    The dbm_ functions provided in this library should not be confused in any
    way with those of a general-purpose database management system. These
    functions do not provide for multiple search keys per entry, they do not
    protect against multi-user access (in other words they do not lock records
    or files), and they do not provide the many other useful database
    functions that are found in more robust database management systems.
    Creating and updating databases by use of these functions is relatively
    slow because of data copies that occur upon hash collisions. These
    functions are useful for applications requiring fast lookup of relatively
    static information that is to be indexed by a single key.

    The dbm_delete(3) function need not physically reclaim file space,
    although it does make it available for reuse by the database.

    After calling dbm_store(3) or dbm_delete(3) during a pass through the keys
    by dbm_firstkey(3) and dbm_nextkey(3), the application should reset the
    database by calling dbm_firstkey(3) before again calling dbm_nextkey(3).
    The contents of these files are unspecified and may not be portable.

  FUTURE DIRECTIONS

    None.

  SEE ALSO

    open(2)

  USAGE NOTES

    None of these functions are thread safe.

    None of these functions are async-signal safe.