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\input texinfo  @c -*- Texinfo -*-
@comment $Id$
@comment %**start of header (This is for running Texinfo on a region.)
@setfilename gdbm.info
@include version.texi
@settitle gdbm manual

@ifinfo
@dircategory Programming & development tools
@direntry
* GDBM: (gdbm).                 The GNU database manager.
@end direntry
@end ifinfo

@c @setchapternewpage odd
@comment %**end of header (This is for running Texinfo on a region.)

@c Use @kwindex for keywords
@defcodeindex kw
@syncodeindex kw cp
@c Use @flindex for files
@defcodeindex fl
@syncodeindex fl cp

@c Merge all indices into a single one
@syncodeindex fn cp
@syncodeindex vr cp
@syncodeindex ky cp
@syncodeindex pg cp
@syncodeindex tp cp

@iftex
@finalout
@end iftex

@copying
This file documents the GNU dbm utility.

Copyright @copyright{} 1989-1999, 2007, 2008, 2009-2011 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being ``The GNU Database
Manager,'' and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled ``GNU Free Documentation
License.''

(a) The FSF's Back-Cover Text is: ``You have the freedom to
copy and modify this GNU manual.  Buying copies from the FSF
supports it in developing GNU and promoting software freedom.''
@end copying

@titlepage
@sp 6
@center @titlefont{GNU dbm}
@sp 2
@center A Database Manager
@sp 2
@center by Philip A.  Nelson, Jason Downs and Sergey Poznyakoff
@sp 4
@center Manual by Pierre Gaumond, Philip A.  Nelson, Jason Downs
@center and Sergey Poznyakoff
@sp 1
@center Edition @value{EDITION}
@sp 1
@center for GNU @code{dbm}, Version @value{VERSION}
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1993-1999, 2007-2011 Free Software Foundation, Inc.
@sp 2

This is Edition @value{EDITION} of the @cite{GNU @code{dbm} Manual},
for @code{gdbm} Version @value{VERSION}.  @*
Last updated @value{UPDATED}

Published by the Free Software Foundation @*
675 Massachusetts Avenue, @*
Cambridge, MA 02139 USA @*

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Free Software Foundation.
@end titlepage
@page

@ifnothtml
@page
@summarycontents
@page
@end ifnothtml
@contents

@ifnottex
@node Top
@top The GNU database manager.

GNU @code{dbm} is a library of functions implementing a hashed database
on a disk file.  This manual documents GNU @code{dbm} Version @value{VERSION}
(@code{gdbm}).  The software was originally written by Philip A.  Nelson.  This
document was originally written by Pierre Gaumond from texts written by
Phil.
@end ifnottex

@menu
Introduction:

* Copying::                    Your rights.
* Intro::                      Introduction to GNU dbm.
* List::                       List of functions.

Functions:

* Open::                       Opening the database.
* Close::                      Closing the database.
* Store::                      Inserting and replacing records in the database.
* Fetch::                      Searching records in the database.
* Delete::                     Removing records from the database.
* Sequential::                 Sequential access to records.
* Reorganization::             Database reorganization.
* Sync::                       Insure all writes to disk have competed.
* Flat files::                 Export and import to Flat file format.
* Errors::                     Convert internal error codes into English.
* Options::                    Setting internal options.
* Locking::                    File locking.

Programs

* testgdbm::                   Test and modify a GDBM database. 
* gdbmexport::                 Export a database into a portable format.  

Other topics:

* Error codes::                Error codes returned by @code{gdbm} calls.
* Variables::                  Two useful variables.
* Compatibility::              Compatibility with UNIX dbm and ndbm.
* Bugs::                       Problems and bugs.

* GNU Free Documentation License::      Document license.
* Index::                       Index
@end menu

@node Copying
@chapter Copying Conditions.
This library is @dfn{free}; this means that everyone is free to use
it and free to redistribute it on a free basis.  GNU @code{dbm} (@code{gdbm})
is not in the public domain; it is copyrighted and there
are restrictions on its distribution, but these restrictions are
designed to permit everything that a good cooperating citizen would want
to do.  What is not allowed is to try to prevent others from further
sharing any version of @code{gdbm} that they might get from
you.@refill

  Specifically, we want to make sure that you have the right to give
away copies @code{gdbm}, that you receive
source code or else can get it if you want it, that you can change these
functions or use pieces of them in new free programs, and that you know
you can do these things.@refill

  To make sure that everyone has such rights, we have to forbid you to
deprive anyone else of these rights.  For example, if you distribute
copies @code{gdbm}, you must give the recipients all
the rights that you have.  You must make sure that they, too, receive or
can get the source code.  And you must tell them their rights.@refill

  Also, for our own protection, we must make certain that everyone finds
out that there is no warranty for anything in the @code{gdbm} distribution.
If these functions are modified by someone else and passed on, we want
their recipients to know that what they have is not what we distributed,
so that any problems introduced by others will not reflect on our
reputation.@refill

@code{Gdbm} is currently distributed under the terms of the GNU General
Public License, Version 3.  (@emph{NOT} under the GNU General Library
Public License.)  A copy the GNU General Public License is included with
the distribution of @code{gdbm}.

@node Intro
@chapter Introduction to GNU @code{dbm}.

GNU @code{dbm} (@code{gdbm}) is a library of database functions that use
extensible hashing and works similar to the standard UNIX @code{dbm}
functions.  These routines are provided to a programmer needing to
create and manipulate a hashed database. (@code{gdbm} is @emph{NOT} a
complete database package for an end user.)

The basic use of @code{gdbm} is to store key/data pairs in a data file.
Each key must be unique and each key is paired with only one data item.
The keys can not be directly accessed in sorted order.  The basic unit
of data in @code{gdbm} is the structure:

@example
  typedef struct @{
             char *dptr;
             int  dsize;
          @} datum;
@end example

This structure allows for arbitrary sized keys and data items.

The key/data pairs are stored in a @code{gdbm} disk file, called a
@code{gdbm} database.  An application must open a @code{gdbm} database
to be able manipulate the keys and data contained in the database.
@code{gdbm} allows an application to have multiple databases open at the
same time.  When an application opens a @code{gdbm} database, it is
designated as a @code{reader} or a @code{writer}.  A @code{gdbm}
database can be opened by at most one writer at a time.  However, many readers
may open the database simultaneously.  Readers and writers can not
open the @code{gdbm} database at the same time.

@node List
@chapter List of functions.

The following is a quick list of the functions contained in the @code{gdbm}
library.  The include file @code{gdbm.h}, that can be included by the user,
contains a definition of these functions.

@example
#include <gdbm.h>

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

The @code{gdbm.h} include file is often in the @file{/usr/local/include}
directory. (The actual location of @code{gdbm.h} depends on your local
installation of @code{gdbm}.)

@node Open
@chapter Opening the database.

@deftypefn {gdbm interface} GDBM_FILE gdbm_open (const char *@var{name}, int @var{block_size}, @
  int @var{flags}, int @var{mode}, void (*fatal_func)(const char *))
Initializes @code{gdbm} system.  If the file has a size of zero bytes, a file
initialization procedure is performed, setting up the initial structure in the
file.

The arguments are:

@table @var
@item name
The name of the file (the complete name, @code{gdbm} does not append any
characters to this name).
@item block_size
It is used during initialization to determine the size of various
constructs.  It is the size of a single transfer from disk to
memory.  This parameter is ignored if the file has been previously
initialized.  The minimum size is 512.  If the value is less than 512,
the file system block size is used, otherwise the value of
@var{block_size} is used.
@item flags
@kwindex GDBM_READER
@kwindex GDBM_WRITER
@kwindex GDBM_WRCREAT
@kwindex GDBM_NEWDB
If @code{flags} is set to @samp{GDBM_READER}, the user wants to just read the
database and any call to @code{gdbm_store} or @code{gdbm_delete} will fail.
Many readers can access the database at the same time.  If @code{flags} is
set to @samp{GDBM_WRITER}, the user wants both read and write access
to the database and requires exclusive access.  If @code{flags} is set
to @samp{GDBM_WRCREAT}, the user wants both read and write access to
the database and wants it created if it does not already exist.  If
@code{flags} is set to @samp{GDBM_NEWDB}, the user want a new database
created, regardless of whether one existed, and wants read and write
access to the new database.

@kwindex GDBM_SYNC
@kwindex GDBM_NOLOCK
@kwindex GDBM_NOMMAP
The following may also be logically or'd into the database flags:
@samp{GDBM_SYNC}, which causes all database operations to be
synchronized to the disk, @samp{GDBM_NOLOCK}, which prevents the library 
from performing any locking on the database file, and @samp{GDBM_NOMMAP},
which disables the memory mapping mechanism.  The option @samp{GDBM_FAST} is
now obsolete, since @code{gdbm} defaults to no-sync mode.  Any error detected
will cause a return value of @samp{NULL} and an appropriate value will be in
@code{gdbm_errno} (@pxref{Variables}).  If no errors occur, a pointer to the
@code{gdbm} file descriptor will be returned.
@item mode
File mode (see
@ifhtml
@uref{http://www.manpagez.com/man/2/chmod},
@end ifhtml
@ifnothtml
@ref{chmod,,change permissions of a file,chmod(2),
chmod(2) man page},
@end ifnothtml
and
@ifhtml
@uref{http://www.manpagez.com/man/2/open}),
@end ifhtml
@ifnothtml
@pxref{open,,open a file,open(2), open(2) man page}),
@end ifnothtml
which is used if the file is created).
@item fatal_func
A function for @code{gdbm} to call if it detects a fatal error.  The only
parameter of this function is a string.  If the value of @samp{NULL} is
provided, @code{gdbm} will use a default function.
@end table

The return value, is the pointer needed by all other functions to
access that @code{gdbm} file.  If the return is the @samp{NULL} pointer,
@code{gdbm_open} was not successful.  The errors can be found in
@code{gdbm_errno} variable (@pxref{Variables, gdbm_errno}).  Available
error codes are discussed in @ref{Error codes}.

In all of the following calls, the parameter @var{dbf} refers to the pointer
returned from @code{gdbm_open}.
@end deftypefn

@node Close
@chapter Closing the database.

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

@deftypefn {gdbm interface} void gdbm_close (GDBM_FILE @var{dbf})
This function closes the @code{gdbm} file and frees all memory
associated with it.  The parameter is:

@table @var
@item dbf
The pointer returned by @code{gdbm_open}.
@end table
@end deftypefn

@node Store
@chapter Inserting and replacing records in the database.

@deftypefn {gdbm interface} int gdbm_store (GDBM_FILE @var{dbf}, datum @var{key}, @
           datum @var{content}, int @var{flag})
The function @code{gdbm_store} inserts or replaces records in the database.

The parameters are:

@table @var
@item dbf
The pointer returned by @code{gdbm_open}.
@item key
The search key.
@item content
The data to be associated with the key.
@item flag
@kwindex GDBM_REPLACE
@kwindex GDBM_INSERT
Defines the action to take when the key is already in the database.  The value
@samp{GDBM_REPLACE} (defined in @file{gdbm.h}) asks that the old data
be replaced by the new @var{content}.  The value @samp{GDBM_INSERT}
asks that an error be returned and no action taken if the @var{key}
already exists.
@end table

This function can return the following values:

@table @asis
@item -1
The item was not stored in the database because the caller was not an
official writer or either @var{key} or @var{content} have a
@samp{NULL} @samp{dptr} field.

Both @var{key} and @var{content} must have the @samp{dptr} field be a
non-@samp{NULL} value.  Since a @samp{NULL} @samp{dptr} field is used by
other func