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GDBM(3)			      GDBM User Reference		       GDBM(3)

NAME
       GDBM - The GNU database manager.	 Includes dbm and ndbm compatibility.

SYNOPSIS
       #include <gdbm.h>

       extern gdbm_error gdbm_errno;
       extern char *gdbm_version;
       GDBM_FILE gdbm_open (const char *name, int block_size,
			    int flags, int mode,
			    void (*fatal_func)(const char *));
       void gdbm_close (GDBM_FILE dbf);
       int gdbm_store (GDBM_FILE dbf, datum key, datum content, int flag);
       datum gdbm_fetch (GDBM_FILE dbf, datum key);
       int gdbm_delete (GDBM_FILE dbf, datum key);
       datum gdbm_firstkey (GDBM_FILE dbf);
       datum gdbm_nextkey (GDBM_FILE dbf, datum key);
       int gdbm_reorganize (GDBM_FILE dbf);
       void gdbm_sync (GDBM_FILE dbf);
       int gdbm_exists (GDBM_FILE dbf, datum key);
       const char *gdbm_strerror (gdbm_error errno);
       int gdbm_setopt (GDBM_FILE dbf, int option, int value, int size);
       int gdbm_fdesc (GDBM_FILE dbf);

   DBM Compatability routines:
       #include <dbm.h>

       int dbminit (const char *name);
       int store (datum key, datum content);
       datum fetch (datum key);
       int delete (datum key);
       datum firstkey (void);
       datum nextkey (datum key);
       int dbmclose (void);

   NDBM Compatability routines:
       #include <ndbm.h>

       DBM *dbm_open (const char *name, int flags, int mode);
       void dbm_close (DBM *file); datumdbm_fetch(DBM*"file, datum key);
       int dbm_store (DBM *file, datum key, datum content, int flags);
       int dbm_delete (DBM *file, datum key);
       datum dbm_firstkey (DBM *file);
       datum dbm_nextkey (DBM *file, datum key);
       int dbm_error (DBM *file);
       int dbm_clearerr (DBM *file);
       int dbm_pagfno (DBM *file);
       int dbm_dirfno (DBM *file);
       int dbm_rdonly (DBM *file);

DESCRIPTION
       GNU  dbm	 is a library of routines that manages data files that contain
       key/data pairs.	The access provided is that of storing, retrieval, and
       deletion	 by  key and a non-sorted traversal of all keys.  A process is
       allowed to use multiple data files at the same time.

       This manpage is a  short	 description  of  the  GDBM  library.	For  a
       detailed	 discussion, including examples of the configuration and usage
       recommendations, refer to the GDBM Manual available in Texinfo  format.
       To access it, run:

	 info gdbm

       Should  any  discrepancies occur between this manpage and the GDBM Man‐
       ual, the later shall be considered the authoritative source.

       A process that opens a gdbm file is  designated	as  a  "reader"	 or  a
       "writer".   Only	 one  writer may open a gdbm file and many readers may
       open the file.  Readers and writers can not open the gdbm file  at  the
       same time. The procedure for opening a gdbm file is:

       GDBM_FILE gdbm_open (const char *name, int block_size,
			    int flags, int mode,
			    void (*fatal_func)(const char *));

       Name  is	 the name of the file (the complete name, gdbm does not append
       any characters to this name).  Block_size  is  the  size	 of  a	single
       transfer from disk to memory. This parameter is ignored unless the file
       is a new file.  The minimum size is 512.	 If it is less than  512,  dbm
       will  use the stat block size for the file system.  Read_write can have
       one of the following values:

       GDBM_READER
	      reader

       GDBM_WRITER
	      writer

       GDBM_WRCREAT
	      writer - if database does not exist create new one

       GDBM_NEWDB
	      writer - create new database regardless if one exists

       The GDBM_NOMMAP added to read_write by bitwise or  instructs  gdbm_open
       to disable the use of mmap(2).

       For the last three (writers of the database) the following may be added
       added to read_write by bitwise or:

       GDBM_SYNC
	      Causes all database operations to be synchronized to the disk,

       GDBM_NOLOCK
	      Pevents the library from performing any locking on the  database
	      file.

       The  option  GDBM_FAST  is now obsolete, since gdbm defaults to no-sync
       mode.

       Mode is the file mode (see chmod(2) and open(2)) if the	file  is  cre‐
       ated.  (*Fatal_func)  ()	 is a function for dbm to call if it detects a
       fatal error. The only parameter of this function is a string.   If  the
       value of 0 is provided, gdbm will use a default function.

       The  return value is the pointer needed by all other routines to access
       that gdbm file.	If the return is the NULL pointer, gdbm_open  was  not
       successful.   The errors can be found in gdbm_errno for gdbm errors and
       in errno for system errors.  (For error codes, see gdbmerrno.h.)

       In all of the following calls, the parameter dbf refers to the  pointer
       returned from gdbm_open.

       It  is important that every file opened is also closed.	This is needed
       to update the reader/writer count on the file.  This is done by:

       void gdbm_close (GDBM_FILE dbf);

       The database is used by 3 primary routines.  The first stores  data  in
       the database.

       int gdbm_store (GDBM_FILE dbf, datum key, datum content, int flag);

       Dbf  is	the pointer returned by gdbm_open.  Key is the key data.  Con‐
       tent is the data to be associated with the key.	Flag can have  one  of
       the following values:

       GDBM_INSERT
	      Insert only, generate an error if key exists;

       GDBM_REPLACE
	      Replace contents if key exists.

       If  a reader calls gdbm_store, the return value will be	-1.  If called
       with GDBM_INSERT and key is in the database, the return value  will  be
       1.  Otherwise, the return value is 0.

       NOTICE:	If  you store data for a key that is already in the data base,
       gdbm  replaces  the  old	 data  with  the  new  data  if	 called	  with
       GDBM_REPLACE.   You  do not get two data items for the same key and you
       do not get an error from gdbm_store.

       NOTICE: The size in gdbm is not restricted like in dbm or  ndbm.	  Your
       data can be as large as you want.

       To search for some data, use:

       datum gdbm_fetch (GDBM_FILE dbf, datum key);

       Dbf is the pointer returned by gdbm_open.  Key is the key data.

       If  the	dptr  element  of the return value is NULL, no data was found.
       Otherwise the return value is a pointer to the found data.  The storage
       space for the dptr element is allocated using malloc(3).	 Gdbm does not
       automatically free this data.  It is the programmer's responsibility to
       free this storage when it is no longer needed.

       To search for some data, without retrieving it:

       int gdbm_exists (GDBM_FILE dbf, datum key);

       Dbf  is	the  pointer  returned	by  gdbm_open.	Key is the key data to
       search for.

       If the key is found within the database, the return value will be true.
       If  nothing  appropiate	is  found, false is returned.  This routine is
       useful for checking for the existence of a record,  without  performing
       the memory allocation done by gdbm_fetch.

       To remove some data from the database:

       int gdbm_delete (GDBM_FILE dbf, datum key);

       Dbf is the pointer returned by gdbm_open.  Key is the key data.

       The return value is -1 if the item is not present or the requester is a
       reader.	The return value is 0 if there was a successful delete.

       The next two routines allow for accessing all items  in	the  database.
       This  access is not key sequential, but it is guaranteed to visit every
       key in the database once.  (The order has to do with the hash values.)

       datum gdbm_firstkey (GDBM_FILE dbf);
       datum gdbm_nextkey (GDBM_FILE dbf, datum key);

       Dbf is the pointer returned by gdbm_open. Key is the key data.

       The return values are both of type datum.  If the dptr element  of  the
       return  value is NULL, there is no first key or next key.  Again notice
       that dptr points to data allocated by malloc(3) and gdbm will not  free
       it for you.

       These  functions were intended to visit the database in read-only algo‐
       rithms, for instance, to validate the database or similar operations.

       File `visiting' is based on a `hash  table'.   gdbm_delete  re-arranges
       the  hash  table	 to  make sure that any collisions in the table do not
       leave some item `un-findable'.  The original key order is  NOT  guaran‐
       teed  to	 remain	 unchanged in ALL instances.  It is possible that some
       key will not be visited if a loop like the following is executed:

	    key = gdbm_firstkey (dbf);
	    while (key.dptr)
	      {
		nextkey = gdbm_nextkey (dbf, key);
		if (some condition)
		  gdbm_delete ( dbf, key );
		free (key.dptr);
		key = nextkey;
	      }

       The following routine should be used very infrequently.

       int gdbm_reorganize (GDBM_FILE dbf);

       If you have had a lot of deletions and would like to shrink  the	 space
       used by the gdbm file, this routine will reorganize the database.  Gdbm
       will not shorten the length of a gdbm file except by using this reorga‐
       nization.  (Deleted file space will be reused.)

       Unless  your database was opened with the GDBM_SYNC flag, gdbm does not
       wait for writes to be flushed to the disk before continuing.  The  fol‐
       lowing routine can be used to guarantee that the database is physically
       written to the disk file.

       void gdbm_sync (GDBM_FILE dbf);

       It will not return until the disk file state is	syncronized  with  the
       in-memory state of the database.

       To convert a gdbm error code into English text, use this routine:

       const char *gdbm_strerror (gdbm_error errno);

       Gdbm now supports the ability to set certain options on an already open
       database.

       int gdbm_setopt (GDBM_FILE dbf, int option, int value, int size);

       Where dbf is the return value from a previous call  to  gdbm_open,  and
       option specifies which option to set.  The valid options are currently:

       GDBM_CACHESIZE
	      Set  the size of the internal bucket cache. This option may only
	      be set once on each GDBM_FILE descriptor, and is	set  automati‐
	      cally to 100 upon the first access to the database.

       GDBM_FASTMODE
	       Set fast mode to either on or off.  This allows fast mode to be
	      toggled on an already  open  and	active	database.  value  (see
	      below)  should  be  set to either TRUE or FALSE.	This option is
	      now obsolete.

       GDBM_SYNCMODE
	      Turn on or off file  system  synchronization  operations.	  This
	      setting  defaults	 to  off;  value  (see below) should be set to
	      either TRUE or FALSE.

       GDBM_CENTFREE
	      Set central free block pool to either on or off.	The default is
	      off, which is how previous versions of Gdbm handled free blocks.
	      If set, this option causes all  subsequent  free	blocks	to  be
	      placed  in the global pool, allowing (in thoery) more file space
	      to be reused more quickly. value (see below) should  be  set  to
	      either  TRUE  or	FALSE.	 NOTICE:  This	feature is still under
	      study.

       GDBM_COALESCEBLKS
	      Set free block merging to either on or off.  The default is off,
	      which  is	 how previous versions of Gdbm handled free blocks. If
	      set, this option causes adjacent free blocks to be merged.  This
	      can become a CPU expensive process with time, though, especially
	      if used in conjunction with  GDBM_CENTFREE.  value  (see	below)
	      should  be set to either TRUE or FALSE.  NOTICE: This feature is
	      still under study.

       value is the value to set option to, specified as an  integer  pointer.
       size  is	 the  size  of the data pointed to by value.  The return value
       will be -1 upon failure,	 or  0	upon  success.	 The  global  variable
       gdbm_errno will be set upon failure.

       For  instance, to set a database to use a cache of 10, after opening it
       with gdbm_open, but prior to accessing it in  any  way,	the  following
       code could be used:

	    int value = 10;

	    ret = gdbm_setopt( dbf, GDBM_CACHESIZE, &value, sizeof(int));

       If the database was opened with the GDBM_NOLOCK flag, the user may wish
       to perform their own file locking on the database file in order to pre‐
       vent multiple writers operating on the same file simultaneously.

       In order to support this, the gdbm_fdesc routine is provided.

       int gdbm_fdesc (GDBM_FILE dbf);

       Where  dbf  is the return value from a previous call to gdbm_open.  The
       return value will be the file descriptor of the database.

       The following two external variables may be useful:

       gdbm_errno is the variable that contains more  information  about  gdbm
       errors.	 (gdbm.h  has  the definitions of the error values and defines
       gdbm_errno as an external variable.)

       gdbm_version is the string containing the version information.

       There are a few more things of interest.	 First,	 gdbm  files  are  not
       "sparse".   You can copy them with the UNIX cp(1) command and they will
       not expand in the copying process.  Also, there is a compatibility mode
       for use with programs that already use UNIX dbm.	 In this compatibility
       mode, no gdbm file pointer is required by the programmer, and only  one
       file  may  be  opened  at  a time.  All users in compatibility mode are
       assumed to be writers.  If the gdbm file is a read only, it  will  fail
       as  a  writer,  but will also try to open it as a reader.  All returned
       pointers in datum structures point to data that gdbm WILL  free.	  They
       should be treated as static pointers (as standard UNIX dbm does).

LINKING
       This  library is accessed by specifying -lgdbm as the last parameter to
       the compile line, e.g.:

	    gcc -o prog prog.c -lgdbm

       If you wish to use the dbm or ndbm  compatibility  routines,  you  must
       link in the gdbm_compat library as well.	 For example:

	    gcc -o prog proc.c -lgdbm -lgdbm_compat

BUG REPORTS
       Send bug reports to <bug-gdbm@gnu.org>.

SEE ALSO
       gdbm_dump(1), gdbm_load(1), gdbmtool(1).

AUTHORS
       by Philip A. Nelson, Jason Downs and Sergey Poznyakoff.

COPYRIGHT
       Copyright © 1990 - 2011 Free Software Foundation, Inc.

       GDBM  is	 free software; you can redistribute it and/or modify it under
       the terms of the GNU General Public License as published	 by  the  Free
       Software	 Foundation;  either  version 1, or (at your option) any later
       version.

       GDBM is distributed in the hope that it will be useful, but WITHOUT ANY
       WARRANTY;  without even the implied warranty of MERCHANTABILITY or FIT‐
       NESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License  for
       more details.

       You should have received a copy of the GNU General Public License along
       with GDBM.  If not, see <http://gnu.org/licenses/gpl.html>

CONTACTS
       You may contact the original author by:
	  e-mail:  phil@cs.wwu.edu
	 us-mail:  Philip A. Nelson
       Computer Science Department
       Western Washington University
       Bellingham, WA 98226

       You may contact the current maintainers by:
	  e-mail:  downsj@downsj.com
       and
	  e-mail:  gray@gnu.org

GDBM				  May 8, 2013			       GDBM(3)
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