dbm(3X)                        DG/UX 5.4R3.00                        dbm(3X)


NAME
       dbminit, fetch, store, delete, firstkey, nextkey - data base
       subroutines

SYNOPSIS
       #include <dbm.h>

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

       dbminit(file)
       char *file;

       dbmclose()

       datum fetch(key)
       datum key;

       store(key, content)
       datum key, content;

       delete(key)
       datum key;

       datum firstkey()

       datum nextkey(key)
       datum key;

DESCRIPTION
       Note: the dbm library has been superseded by ndbm(3C), and is now
       implemented using ndbm.  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.  The functions are obtained with the loader option
       -ldbm.

       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 dbminit.  At
       the time of this call, the files file.dir and file.pag must exist.
       (An empty database is created by creating zero-length `.dir' and
       `.pag' files.)

       A database may be closed by calling dbmclose.  You must close a
       database before opening a new one.




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dbm(3X)                        DG/UX 5.4R3.00                        dbm(3X)


       Once open, the data stored under a key is accessed by fetch and data
       is placed under a key by store.  A key (and its associated contents)
       is deleted by delete.  A linear pass through all keys in a database
       may be made, in an (apparently) random order, by use of firstkey and
       nextkey.  Firstkey will return the first key in the database.  With
       any key nextkey will return the next key in the database.  This code
       will traverse the data base:

              for (key = firstkey(); key.dptr != NULL; key = nextkey(key))

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.

SEE ALSO
       ndbm(3C).

NOTES
       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).  Moreover all key/content
       pairs that hash together must fit on a single block.  Store will
       return an error in the event that a disk block fills with inseparable
       data.

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

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


















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