dbm(3X)                 (BSD Compatibility Package)                 dbm(3X)


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

   SYNOPSIS
         cc [ flag... ] file ...  -ldbm

         #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         Note: the dbm library has been superceded by ndbm(3), and is now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 -libdbm.

         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.





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   dbm(3X)                 (BSD Compatibility Package)                 dbm(3X)


         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.

         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))

   SEE ALSO
         ndbm(3).

   RETURN VALUE
         All functions that return an int indicate errors with negative
         values.  A zero return indicates no error.  Routines that return a
         datum indicate errors with a NULL (0) dptr.

   NOTES
         The .pag file will contain holes so that its apparent size is about
         four times its actual content.  Older versions of the UNIX operating
         system may create real file blocks for these holes when touched.
         These files cannot be copied by normal means (cp(1), cat(1), tar(1),
         ar(1)) 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.

         There are no interlocks and no reliable cache flushing; thus
         concurrent updating and reading is risky.



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