dbm(3BSD)            (BSD System Compatibility)            dbm(3BSD)


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

       SYNOPSIS
             /usr/ucb/cc [flag . . . ] file . . .
             #include <dbm.h>
             typedef struct {
                 char *dptr;
                 int dsize;
             } datum;
             dbminit(const char *file);
             dbmclose(void);
             datum fetch(datum key);
             store(datum key, datum content);
             delete(datum key);
             datum firstkey(void);
             datum nextkey(datum key);

       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.  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.

             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


                           Copyright 1994 Novell, Inc.               Page 1

      dbm(3BSD)            (BSD System Compatibility)            dbm(3BSD)


            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))

      REFERENCES
            ndbm(3BSD)

      Return Values
            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.

      NOTICES
            The dbm library has been superseded by ndbm(3BSD), and is now
            implemented using ndbm.

            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 [that is, 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.







                          Copyright 1994 Novell, Inc.               Page 2