# 2.11BSD#431 - /usr/man/cat3/delete.0

    DBM(3X)             UNIX Programmer's Manual		  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;

         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         Note: the dbm library has been superceded by ndbm(3), and is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 func-
         tions 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 suf-
         fix.  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

    Printed 11/26/99	  May 12, 1986				1

    DBM(3X)             UNIX Programmer's Manual		  DBM(3X)

         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 nega-
         tive values.  A zero return indicates ok.	Routines that
         return a datum indicate errors with a null (0) dptr.

    SEE ALSO
         ndbm(3)

    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 sin-
         gle 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.

    Printed 11/26/99	  May 12, 1986				2

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