ndbm(3)                    DG/UX 4.30                     ndbm(3)



     NAME
          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 *dbmopen(file, flags, mode)
              char *file;
              int flags, mode;

          void dbmclose(db)
              DBM *db;

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

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

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

          datum dbmfirstkey(db)
              DBM *db;

          datum dbmnextkey(db)
              DBM *db;

          int dbmerror(db)
              DBM *db;

          int dbmclearerr(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.




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     ndbm(3)                    DG/UX 4.30                     ndbm(3)



          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 parameter (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 DBMINSERT or DBMREPLACE.
          DBMINSERT will only insert new entries into the database
          and will not change an existing entry with the same key.
          DBMREPLACE 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 DBMINSERT 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 4096 bytes).  Moreover
          all key/content pairs that hash together must fit on a



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     ndbm(3)                    DG/UX 4.30                     ndbm(3)



          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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