DBM(3X)                              BSD                               DBM(3X)



NAME
     dbminit, fetch, store, delete, firstkey, nextkey - database subroutines

SYNOPSIS
     #include <dbm.h>

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

     dbminit(file)
     char *file;

     datum fetch(key)
     datum key;

     store(key, content)
     datum key, content;

     delete(key)
     datum key;

     datum firstkey()

     datum nextkey(key)
     datum key;

DESCRIPTION
     The dbm library has been superceded by ndbm(3) and is now implemented
     using ndbm.

     These functions maintain key/content pairs in a database.  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 database 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.)

     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 can 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
     database:

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

SEE ALSO
     ndbm(3)

DIAGNOSTICS
     All functions that return an int indicate errors with negative values.  A
     0 return indicates ok.  Routines that return a datum indicate errors with
     a null (0) dptr.

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).  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.