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

    NDBM(3)             UNIX Programmer's Manual		  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 *dbm_open(file, flags, mode)
    	 char *file;
    	 int flags, mode;

         void dbm_close(db)
    	 DBM *db;

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

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

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

         datum dbm_firstkey(db)
    	 DBM *db;

         datum dbm_nextkey(db)
    	 DBM *db;

         int dbm_error(db)
    	 DBM *db;

         int dbm_clearerr(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.

    Printed 11/26/99	  May 20, 1986				1

    NDBM(3)             UNIX Programmer's Manual		  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 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
         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 DBM_INSERT or DBM_REPLACE.
         DBM_INSERT will only insert new entries into the database
         and will not change an existing entry with the same key.
         DBM_REPLACE 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 read-
         ing or writing the database.  Dbm_clearerr resets the error
         condition on the named database.

    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. If
         dbm_store called with a flags value of DBM_INSERT 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

    Printed 11/26/99	  May 20, 1986				2

    NDBM(3)             UNIX Programmer's Manual		  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)

    Printed 11/26/99	  May 20, 1986				3

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