ndbm(3C)                       DG/UX R4.11MU05                      ndbm(3C)


NAME
       ndbm: dbm_open, dbm_close, dbm_fetch, dbm_store, dbm_delete,
       dbm_firstkey, dbm_nextkey, dbm_error, dbm_clearerr - data base
       subroutines

SYNOPSIS
       #include <ndbm.h>

       typedef struct {
           char *dptr;
           int dsize;
       } datum;

       DBM *dbm_open(file, flags, mode)
           char *file;
           int flags, mode;

       void dbm_close(db)
           DBM *db;

       datum dbm_fetch(db, key)
           DBM *db;
           datum key;

       int dbm_store(db, key, content, flags)
           DBM *db;
           datum key, content;
           int flags;

       int dbm_delete(db, key)
           DBM *db;
           datum key;

       datum dbm_firstkey(db)
           DBM *db;

       datum dbm_nextkey(db)
           DBM *db;

       int dbm_error(db)
           DBM *db;

       int dbm_clearerr(db)
           DBM *db;

DESCRIPTION
       These functions maintain key/content pairs in a data base.  The
       functions will handle very large (a billion blocks) databases and
       will access a keyed item in one or two file system accesses.  This
       package replaces the earlier dbm(3X) library, which managed only a
       single database.

       Keys and contents are described by the datum typedef.  A datum
       specifies a string of dsize bytes pointed to by dptr.  Arbitrary
       binary data, as well as normal ASCII strings, are allowed.  The data
       base is stored in two files.  One file is a directory containing a
       bit map and has `.dir' as its suffix.  The second file contains all
       data and has `.pag' as its suffix.

       Before a database can be accessed, it must be opened by dbm_open.
       This will open and/or create the files file.dir and file.pag
       depending on the flags and mode parameters (see open(2)).

       Once open, the data stored under a key is accessed by dbm_fetch and
       data is placed under a key by dbm_store.  The flags field can be
       either DBM_INSERT or DBM_REPLACE.  DBM_INSERT will only insert new
       entries into the database and will not change an existing entry with
       the same key.  DBM_REPLACE will replace an existing entry if it has
       the same key.  A key (and its associated contents) is deleted by
       dbm_delete.  A linear pass through all keys in a database may be
       made, in an (apparently) random order, by use of dbm_firstkey and
       dbm_nextkey.  Dbm_firstkey will return the first key in the database.
       Dbm_nextkey will return the next key in the database.  This code will
       traverse the data base:

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

       Dbm_error returns non-zero when an error has occurred reading or
       writing the database.  Dbm_clearerr resets the error condition on the
       named database.

DIAGNOSTICS
       All functions that return an int indicate errors with negative
       values.  A zero return indicates ok.  Routines that return a datum
       indicate errors with a null (0) dptr.  If dbm_store called with a
       flags value of DBM_INSERT finds an existing entry with the same key
       it returns 1.

BUGS
       The `.pag' file will contain holes so that its apparent size is about
       four times its actual content.  Older UNIX systems may create real
       file blocks for these holes when touched.  These files cannot be
       copied by normal means (cp, cat, tp, tar, ar) without filling in the
       holes.

       Dptr pointers returned by these subroutines point into static storage
       that is changed by subsequent calls.

       The sum of the sizes of a key/content pair must not exceed the
       internal block size (currently 1024 bytes - 6 bytes of overhead).
       Moreover all key/content pairs that hash together must fit on a
       single block.  Dbm_store will return an error in the event that a
       disk block fills with inseparable data.

       Dbm_delete does not physically reclaim file space, although it does
       make it available for reuse.

       The order of keys presented by dbm_firstkey and dbm_nextkey depends
       on a hashing function, not on anything interesting.

SEE ALSO
       dbm(3X)


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