NDBM(3) 						     Library Functions 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.

       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
       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 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 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 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)

4.3 Berkeley Distribution					   May 20, 1986 							   NDBM(3)