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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 functions to indicate an error, it cannot be valid data.
@item +1
The item was not stored because the argument @var{flag} was
@samp{GDBM_INSERT} and the @var{key} was already in the database.
@item 0
No error.  The value of @var{content} is keyed by @var{key}.  The file
on disk is updated to reflect the structure of the new database before
returning from this function.
@end table
@end deftypefn

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

The size in @code{gdbm} is not restricted like @code{dbm} or @code{ndbm}.  Your
data can be as large as you want.

@node Fetch
@chapter Searching for records in the database.

@deftypefn {gdbm interface} datum gdbm_fetch (GDBM_FILE @var{dbf}, datum @var{key})
Looks up a given @var{key} and returns the information associated with it.
The @samp{dptr} field in the structure that is returned points to a
memory block allocated by @code{malloc}.  It is the caller's
responsibility to free it when no longer needed.

If the @samp{dptr} is @samp{NULL}, no data was found.

The parameters are:

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

An example of using this function:

@example
content = gdbm_fetch (dbf, key);
if (content.dptr == NULL)
  @{
    fprintf(stderr, "key not found\n");
  @}
else
  @{
    /* do something with content.dptr */
  @}
@end example

You may also search for a particular key without retrieving it:

@deftypefn {gdbm interface} int gdbm_exists (GDBM_FILE @var{dbf}, datum @var{key})
Returns @samp{true} (@samp{1}) if the @var{key} exists in @var{dbf}
and @samp{false} (@samp{0}) otherwise.

The parameters are:

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

@node Delete
@chapter Removing records from the database.

To remove some data from the database, use the @code{gdbm_delete}
function.

@deftypefn {gdbm interface} int gdbm_delete (GDBM_FILE @var{dbf}, datum @var{key})
Deletes the data associated with the given @var{key}, if it exists in
the database @var{dbf}.  The file on disk is updated to reflect the
structure of the new database before returning from this function.

The parameters are:

@table @var
@item dbf
The pointer returned by @code{gdbm_open}.
@item datum key
The search key.
@end table

The function returns @samp{-1} if the item is not present or the
requester is a reader.  The return of @samp{0} marks a successful delete.
@end deftypefn

@node Sequential
@chapter Sequential access to records.

The next two functions allow for accessing all items in the database.  This
access is not @code{key} sequential, but it is guaranteed to visit every
@code{key} in the database once.  The order has to do with the hash values.
@code{gdbm_firstkey} starts the visit of all keys in the database.
@code{gdbm_nextkey} finds and reads the next entry in the hash structure for
@code{dbf}.

@deftypefn {gdbm interface} datum gdbm_firstkey (GDBM_FILE @var{dbf})
Initiate sequential access to the database @var{dbf}.  The returned
value is the first key accessed in the database.  If the @samp{dptr}
field in the returned datum is @samp{NULL}, the database contains no
data.

Otherwise, @samp{dptr} points to a memory block obtained from
@code{malloc}, which holds the key value.  The caller is responsible
for freeing this memory block when no longer needed.
@end deftypefn

@deftypefn {gdbm interface} datum gdbm_nextkey (GDBM_FILE @var{dbf}, datum @var{prev})
This function continues the iteration over the keys in @var{dbf},
initiated by @code{gdbm_firstkey}.  The parameter @var{prev} holds the
value returned from a previous call to @code{gdbm_nextkey} or
@code{gdbm_firstkey}.

The function returns next key from the database.  If the @samp{dptr}
field in the returned datum is @samp{NULL}, all keys in the database
has been visited.

Otherwise, @samp{dptr} points to a memory block obtained from
@code{malloc}, which holds the key value.  The caller is responsible
for freeing this memory block when no longer needed.
@end deftypefn

These functions were intended to visit the database in read-only algorithms,
for instance, to validate the database or similar operations.  The
usual algorithm for sequential access is:

@example
@group
   key = gdbm_firstkey (dbf);
   while (key.dptr)
     @{
        datum nextkey;

        /* do something with the key */
        ...

        /* Obtain the next key */
        nextkey = gdbm_nextkey (dbf, key);
        /* Reclaim the memory used by the key */
        free (key.dptr);
        /* Use nextkey in the next iteration. */
        key = nextkey;
     @}
@end group
@end example

Care should be taken when the @code{gdbm_delete} function is used in
such a loop.  File visiting is based on a @dfn{hash table}.  The
@code{gdbm_delete} function re-arranges the hash table to make sure
that any collisions in the table do not leave some item
@dfn{un-findable}.  The original key order is @emph{not} guaranteed to
remain unchanged in all instances.  So it is possible that some key
will not be visited if a loop like the following is executed:

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

@node Reorganization
@chapter Database reorganization.

The following function should be used very seldom.

@deftypefn {gdbm interface} int gdbm_reorganize (GDBM_FILE @var{dbf})
Reorganizes the database.

The parameter is:

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

If you have had a lot of deletions and would like to shrink the space
used by the @code{gdbm} file, this function will reorganize the database.
This results, in particular, in shortening the length of a @code{gdbm}
file by removing the space occupied by deleted records.

This reorganization requires creating a new file and inserting all the elements
in the old file @var{dbf} into the new file.  The new file is then renamed to
the same name as the old file and @var{dbf} is updated to contain all the
correct information about the new file.  If an error is detected, the return
value is negative.  The value zero is returned after a successful
reorganization.

@node Sync
@chapter Database Synchronization

@kwindex GDBM_SYNC
Unless your database was opened with the @samp{GDBM_SYNC} flag,
@code{gdbm} does not wait for writes to be flushed to the disk before
continuing.  This allows for faster writing of databases at the risk
of having a corrupted database if the application terminates in an
abnormal fashion.  The following function allows the programmer to
make sure the disk version of the database has been completely updated
with all changes to the current time.

@deftypefn {gdbm interface} void gdbm_sync (GDBM_FILE @var{dbf})
Synchronizes the changes in @var{dbf} with its disk file.  The
parameter is a pointer returned by @code{gdbm_open}.

This function would usually be called after a complete set of changes
have been made to the database and before some long waiting time.
The @code{gdbm_close} function automatically calls the equivalent of
@code{gdbm_sync} so no call is needed if the database is to be closed
immediately after the set of changes have been made.
@end deftypefn

@node Flat files
@chapter Export and Import
@cindex Flat file format
@cindex export
@cindex import
@code{Gdbm} databases can be converted into a protable @dfn{flat
format}.  This format can be used, for example, to migrate between
the different versions of @code{gdbm} databases.  Generally speaking,
flat files are safe to send over the network, and can be used to
recreate the database on another machine.  The recreated database is
guaranteed to be a byte-to-byte equivalent of the database from which
the flat file was created.  This does not necessarily mean, however,
that this file can be used in the same way as the original one.  For
example, if the original database contained non-@acronym{ASCII} data
(e.g.  @acronym{C} structures, integers etc.), the recreated database
can be of any use only if the target machine has the same integer
size and byte ordering as the source one and if its @acronym{C}
compiler uses the same packing conventions as the one which generated
@acronym{C} which populated the original database.  In general, such
binary databases are not portable between machines, unless you follow
some stringent rules on what data is written to them and how it is
interpreted.

@deftypefn {gdbm interface} int gdbm_export (GDBM_FILE @var{dbf}, @
           const char *@var{exportfile}, int @var{flag}, int @var{mode})
Create a flat file from the @code{gdbm} database.  The parameters are:

@table @var
@item dbf
A pointer to the source database, returned by a call to
@code{gdbm_open}.  The database must be open in @samp{GDBM_WRITER} mode.

@item exportfile
The name of the output file.

@item flag
@kwindex GDBM_WRCREAT
@kwindex GDBM_NEWDB
How to create the output file.  If @var{flag} is @samp{GDBM_WRCREAT},
the file will be created if it does not exist already.  Otherwise, if
it is @samp{GDBM_NEWDB}, it will be created if it does not exist, and
truncated otherwise.

@item mode
The permissions to use when creating the output file.
See @ifhtml
@uref{http://www.manpagez.com/man/2/open},
@end ifhtml
@ifnothtml
@ref{open,,open a file,open(2), open(2) man page},
@end ifnothtml
for a detailed discussion.
@end table
@end deftypefn

@deftypefn {gdbm interface} int gdbm_import (GDBM_FILE @var{dbf}, @
           const char *@var{importfile}, int @var{flag})
Populates the database from an existing flat file.

@table @var
@item dbf
A pointer to the source database, returned by a call to
@code{gdbm_open}.  The database must be open in @samp{GDBM_WRITER} mode.

@item importfile
The name of the input flat file.  The file must exist.

@item flag
The @var{flag} argument to be passed to @code{gdbm_store} function
when adding new records.  @xref{Store}, for a description of its
effect.
@end table
@end deftypefn

See also @ref{gdbmexport}, @ref{testgdbm export}, and
@ref{testgdbm import}.

@node Errors
@chapter Error strings.

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

@deftypefn {gdbm interface} const char *gdbm_strerror (gdbm_error @var{errno})
Converts @var{errno} (which is an integer value) into a human-readable
descriptive text.  Returns a pointer to a static string.  The caller
must not alter or free the returned pointer.

The @var{errno} argument is usually the value of the global variable
@code{gdbm_errno}.  @xref{Variables, gdbm_errno}.
@end deftypefn

@node Options
@chapter Setting options.

@code{Gdbm} supports the ability to set certain options on an already
open database.

@deftypefn {gdbm interface} int gdbm_setopt (GDBM_FILE @var{dbf}, int @var{option}, @
           int *@var{value}, int @var{size})
Sets an option on the database.

The parameters are:

@table @var
@item dbf
The pointer returned by @code{gdbm_open}.
@item option
The option to be set.
@item value
A pointer to the value to which @var{option} will be set.
@item size
The length of the data pointed to by @var{value}.
@end table
@end deftypefn

The valid options are:

@table @asis
@kwindex GDBM_CACHESIZE
@item 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 automatically to 100
upon the first access to the database.  The @var{value} should point
to an integer holding the desired cache size.

@kwindex GDBM_FASTMODE
@item GDBM_FASTMODE
@emph{This option is now obsolete and has no effect.  The following
description reflects its historical usage:}

Enable or disable the fast mode.  This allows fast mode to be toggled
on an already open and active database.  The @var{value} should point
to an integer: @samp{TRUE} to enable fast mode, and @samp{FALSE} to disable
it.

@kwindex GDBM_SYNCMODE
@item GDBM_SYNCMODE
Turn on or off file system synchronization operations.  This
setting defaults to off.  The @var{value} should point
to an integer: @samp{TRUE} to turn synchronization on, and @samp{FALSE} to
turn it off.

@kwindex GDBM_CENTFREE
@item GDBM_CENTFREE
@emph{NOTICE: This feature is still under study.}

Set central free block pool to either on or off.  The default is off,
which is how previous versions of @code{gdbm} handled free blocks.  If
set, this option causes all subsequent free blocks to be placed in the
@emph{global} pool, allowing (in theory) more file space to be reused
more quickly.  The @var{value} should point to an integer: @samp{TRUE} to
turn central block pool on, and @samp{FALSE} to turn it off.

@kwindex GDBM_COALESCEBLKS
@item GDBM_COALESCEBLKS
@emph{NOTICE: This feature is still under study.}

Set free block merging to either on or off.  The default is off, which
is how previous versions of @code{gdbm} handled free blocks.  If set,
this option causes adjacent free blocks to be merged.  This can become
a @acronym{CPU} expensive process with time, though, especially if
used in conjunction with GDBM_CENTFREE.  The @var{value} should point
to an integer: @samp{TRUE} to turn free block merging on, and @samp{FALSE} to
turn it off.
@end table

The return value will be @samp{-1} upon failure, or @samp{0} upon
success.  The global variable @code{gdbm_errno} will be set upon failure.

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

@example
@group
int value = 10;
ret = gdbm_setopt(dbf, GDBM_CACHESIZE, &value, sizeof(int));
@end group
@end example

@node Locking
@chapter File Locking.

@kwindex GDBM_NOLOCK
With locking disabled (if @code{gdbm_open} was called with @samp{GDBM_NOLOCK}),
the user may want to perform their own file locking on the database file
in order to prevent multiple writers operating on the same file
simultaneously.

In order to support this, the @code{gdbm_fdesc} routine is provided.

@deftypefn {gdbm interface} int gdbm_fdesc (GDBM_FILE @var{dbf})
Returns the file descriptor of the database @var{dbf}.  This value
can be used as an argument to @code{flock}, @code{lockf} or similar
calls.
@end deftypefn

@node testgdbm
@chapter Test and modify a GDBM database.

The @command{testgdbm} utility allows you to view and modify an
existing @acronym{GDBM} database or to create a new one.

@cindex default database, @command{testgdbm} 
@cindex @option{-g}, @command{testgdbm} option
@flindex junk.gdbm
When invoked without options, it tries to open a database file called
@file{junk.gdbm}, located in the current working directory.  You can
change this default using the @option{-g} command line option.  This
option takes a single argument, specifying the file name to open, e.g.:

@example
$ testgdbm -g file.db
@end example

@cindex read-only mode, @command{testgdbm}
@cindex @option{-r}, @command{testgdbm} option
The database will be opened in read-write mode, unless the @option{-r}
option is specified, in which case it will be opened only for reading.

@cindex creating a database, @command{testgdbm}
@cindex @option{-n}, @command{testgdbm} option
If the database does not exist, @command{testgdbm} will create it.
There is a special option @option{-n}, which instructs the utility to
create a new database.  If it is used and if the database already
exists, it will be deleted, so use it sparingly.

@menu
* invocation::
* shell::
@end menu

@node invocation
@section testgdbm invocation

The following table summarizes all @command{testgdbm} command line
options:

@table @option
@item -b @var{size}
Set block size.
@item -c @var{size}
Set cache size.
@item -g @var{file}
Operate on @var{file} instead of the default @file{junk.gdbm}.
@item -h
Print a concise help summary.
@item -n
Create the database.
@item -r
Open the database in read-only mode.
@item -s
Synchronize to the disk after each write.
@item -v
Print program version and licensing information and exit.
@end table

@node shell
@section testgdbm interactive mode
After successful startup, @command{testgdbm} starts a loop, in which
it reads commands from the user, executes them and prints the results
on the standard output.  If the standard input is attached to a console,
@command{testgdbm} runs in interactive mode, which is indicated by its
@dfn{prompt}:

@example
com -> _
@end example

The utility finishes when it reads the @samp{q} command (see below) or
it detects end-of-file on its standard input, whichever occurs first.

A @command{testgdbm} command consists of a @dfn{command letter},
optionally followed by one or two @dfn{arguments}, separated by any
amount of white space.  An argument is any sequence of non-whitespace
characters.  Notice, that currently there is no way to enter arguments
containing white space.  This limitation will be removed in future
releases.

Each command letter takes at most two @dfn{formal parameters}, which can be
optional or mandatory.  If the number of actual arguments is less than the
number of mandatory parameters, @command{testgdbm} will prompt you to
supply missing arguments.  For example, the @samp{s} command takes two
mandatory parameters, so if you invoked it with no arguments, you
would be prompted twice to supply the necessary data, as shown in 
example below:

@example
com -> @kbd{s}
key -> @kbd{three}
data -> @kbd{3}
@end example

However, such prompting is possible only in interactive mode.  In
non-interactive mode (e.g. when running a script), all arguments must
be supplied with each command, otherwise @command{testgdbm} reports an
error and exits immediately.

@anchor{pager}
@cindex pager, @command{testgdbm}
@cindex @env{PAGER}
Some commands produce excessive amounts of output.  To help you follow
it, @command{testgdbm} will use a pager utility to display such
output.  The name of the pager utility is taken from the environment
variable @env{PAGER}.  The pager is invoked only in interactive mode
and only if the estimated number of output lines is greater then the
number of lines on your screen.  

@anchor{nul-termination}
Many of the @command{testgdbm} commands operate on database key and
data values.  The utility assumes that both keys and data are
@acronym{ASCII} strings, either nul-terminated or not.  By default,
it is assumed that strings are nul-terminated.  You can change this
by using @code{z} (for keys) and @code{Z} (for data) commands.

The following table summarizes all available commands:

@table @code
@item c
Print the number of entries in the database.
@item d @var{key}
Delete entry with a given @var{key}
@anchor{testgdbm export}
@item e @var{file-name} [truncate]
Export the database to the flat file @var{file-name}.  @xref{Flat files},
for a description of the flat file format and its purposes.  This
command will not overwrite an existing file, unless the word
@samp{truncate} is given as its second argument.

See also @ref{gdbmexport}.

@item f @var{key}
Fetch and display a record with the given @var{key}.

@anchor{testgdbm import}
@item i @var{file-name} [replace]
Import data from a flat dump file @var{file-name}
(@pxref{Flat files}).  If the word @samp{replace} is given
as the second argument, any records with the same keys as the already
existing ones will replace them.

@item l
List the contents of the database (@pxref{pager}).

@item n [@var{key}]
@itemx 2
Sequential access: fetch and display a next record.  If @var{key} is
given, a record following one with this key will be fetched.
Otherwise, the key supplied by the latest @code{1}, @code{2} or
@var{n} command will be used.

The second form, @code{2} is a synonym for @code{n} without arguments.

See also @code{1}, below.

@xref{Sequential}, for more information on sequential access.

@item q
Close the database and quit the utility.

@item s @var{key} @var{data}
Store the @var{data} with @var{key} in the database.  If @var{key}
already exists, its data will be replaced.

@item 1
Fetch and display the first record in the database.  Subsequent
records can be fetched using @code{n} (or @code{2}) command (see above). 
@xref{Sequential}, for more information on sequential access.

@item < @var{file} [replace]
Read entries from @var{file} and store them in the database.  If the
word @samp{replace} is given as the second argument, any existing
records with matching keys will be replaced.

@item r
Reorganize the database (@pxref{Reorganization}).

@item z
Toggle key nul-termination.  Use @code{S} to inspect the current
state.  @xref{nul-termination}.

@item A
Print the @dfn{avail list}.

@item B @var{num} 
Print a bucket number @var{num}.  This command uses pager
(@pxref{pager}).

@item C
Print the current bucket.  This command uses pager (@pxref{pager}).

@item D
Print hash directory.  Uses pager (@pxref{pager}).

@item F
Print file header.

@item H @var{key}
Compute and display the hash value for the given @var{key}.

@item K
Print the bucket cache.  Uses pager (@pxref{pager}).

@item S
Print current program status.  The following example shows the
information displayed:

@example
Database file: junk.gdbm
Zero terminated keys: yes
Zero terminated data: yes
@end example

@item V
Print the version of @command{gdbm}.

@item Z
Toggle data nul-termination.  Use @command{S} to examine the current
status.

@xref{nul-termination}.

@item ?
Print a concise command summary, showing each command letter with its
parameters and a short description of what it does.  Optional
arguments are enclosed in square brackets.

@item q
Quit the program.
@end table

@node gdbmexport
@chapter Export a database into a portable format.

The @command{gdbmexport} utility converts the database into a portable
@dfn{flat format}.  Files in this format can be used to populate
databases using the @code{gdbm_import} function (@pxref{Flat files,
gdbm_import}) or the @code{i} command of @command{testgdbm} utility
(@pxref{testgdbm import}).  In many cases files in this format are suitable for
sending over the network to populate the database on another machine.
The only exception to this are databases whose records contain
non-@acronym{ASCII} data (e.g.  @acronym{C} structures, integers
etc.).  For such databases you will be better off by writing a
specialized utility to convert them to an architecture-independent
format.

If @command{gdbmexport} is linked with @file{libgdbm}
version 1.8.3, it can be used to convert databases from old to new
format.

The utility takes two mandatory arguments: the name of the database
file to convert and the output file name, e.g.:

@example
$ gdbmexport junk.gdbm junk.flat
@end example

In addition two options are understood:

@table @option
@item -h
Display short usage summary and exit.

@item -v
Display program version and licensing information, and exit.
@end table

@node Variables
@chapter Useful global variables.

The following global variables and constants are available:

@deftypevar gdbm_error gdbm_errno
This variable contains error code from the last failed @code{gdbm}
call.  @xref{Error codes}, for a list of available error codes and
their descriptions.

Use @code{gdbm_strerror} (@pxref{Errors}) to convert it to a
descriptive text.
@end deftypevar

@deftypevar const char *gdbm_version
A string containing the version information.
@end deftypevar

@deftypevar int const gdbm_version_number[3]
This variable contains the @code{gdbm} version numbers:

@multitable @columnfractions 0.4 0.5
@headitem Index @tab Meaning
@item 0         @tab Major number
@item 1         @tab Minor number
@item 2         @tab Patchlevel number
@end multitable

Additionally, the following constants are defined in the @file{gdbm.h}
file:

@table @asis
@kwindex GDBM_VERSION_MAJOR
@item GDBM_VERSION_MAJOR
Major number.

@kwindex GDBM_VERSION_MINOR
@item GDBM_VERSION_MINOR
Minor number.

@kwindex GDBM_VERSION_PATCH
@item GDBM_VERSION_PATCH
Patchlevel number.
@end table

These can be used to verify whether the header file matches the library.
@end deftypevar

@deftypevar const char * const gdbm_errlist[]
This variable is an array of error descriptions, which is used by
@code{gdbm_strerror} to convert error codes to human-readable text
(@pxref{Errors}).  You can access it directly, if you wish so.  It
contains @code{_GDBM_MAX_ERRNO + 1} elements and can be directly
indexed by the error code to obtain a corresponding descriptive
text.
@end deftypevar

@defvr {Constant} _GDBM_MIN_ERRNO
The minimum error code used by @code{gdbm}.
@end defvr

@defvr {Constant} _GDBM_MAX_ERRNO
The maximum error code used by @code{gdbm}.
@end defvr

@node Error codes
@chapter Error codes

This chapter summarizes the error codes which can be set by the
functions in @code{gdbm} library.

@table @asis
@kwindex GDBM_NO_ERROR
@item GDBM_NO_ERROR
No error occurred.

@kwindex GDBM_MALLOC_ERROR
@item GDBM_MALLOC_ERROR
Memory allocation failed.  Not enough memory.

@kwindex GDBM_BLOCK_SIZE_ERROR
@item GDBM_BLOCK_SIZE_ERROR
This error is set by the @code{gdbm_open} function (@pxref{Open}), if
the value of its @var{block_size} argument is incorrect.

@kwindex GDBM_FILE_OPEN_ERROR
@item GDBM_FILE_OPEN_ERROR
The library was not able to open a disk file.  This can be set by
@code{gdbm_open} (@pxref{Open}), @code{gdbm_export} and
@code{gdbm_import} functions (@pxref{Flat files}).

@kwindex GDBM_FILE_WRITE_ERROR
@item GDBM_FILE_WRITE_ERROR
Writing to a disk file failed.  This can be set by
@code{gdbm_open} (@pxref{Open}), @code{gdbm_export} and
@code{gdbm_import} functions.

@kwindex GDBM_FILE_SEEK_ERROR
@item GDBM_FILE_SEEK_ERROR
Positioning in a disk file failed.  This can be set by
@code{gdbm_open} (@pxref{Open}) function.

@kwindex GDBM_FILE_READ_ERROR
@item GDBM_FILE_READ_ERROR
Reading from a disk file failed.  This can be set by
@code{gdbm_open} (@pxref{Open}), @code{gdbm_export} and
@code{gdbm_import} functions.

@kwindex GDBM_BAD_MAGIC_NUMBER
@item GDBM_BAD_MAGIC_NUMBER
The file given as argument to @code{gdbm_open} function is not a valid
@code{gdbm} file: it has a wrong magic number.

@kwindex GDBM_EMPTY_DATABASE
@item GDBM_EMPTY_DATABASE
The file given as argument to @code{gdbm_open} function is not a valid
@code{gdbm} file: it has zero length.

@kwindex GDBM_CANT_BE_READER
@item GDBM_CANT_BE_READER
This error code is set by the @code{gdbm_open} function if it is not
able to lock file when called in @samp{GDBM_READER} mode (@pxref{Open,
GDBM_READER}).

@kwindex GDBM_CANT_BE_WRITER
@item GDBM_CANT_BE_WRITER       
This error code is set by the @code{gdbm_open} function if it is not
able to lock file when called in writer mode (@pxref{Open}).

@kwindex GDBM_READER_CANT_DELETE
@item GDBM_READER_CANT_DELETE
Set by the @code{gdbm_delete} (@pxref{Delete}) if it attempted to
operate on a database that is open in read-only mode (@pxref{Open,
GDBM_READER}).

@kwindex GDBM_READER_CANT_STORE
@item GDBM_READER_CANT_STORE    
Set by the @code{gdbm_store} (@pxref{Store}) if it attempted to
operate on a database that is open in read-only mode (@pxref{Open,
GDBM_READER}).

@kwindex GDBM_READER_CANT_REORGANIZE
@item GDBM_READER_CANT_REORGANIZE       
Set by the @code{gdbm_reorganize} (@pxref{Reorganization}) if it attempted to
operate on a database that is open in read-only mode (@pxref{Open,
GDBM_READER}).

@kwindex GDBM_UNKNOWN_UPDATE
@item GDBM_UNKNOWN_UPDATE
Currently unused.  Reserved for future uses.

@kwindex GDBM_ITEM_NOT_FOUND
@item GDBM_ITEM_NOT_FOUND
Requested item was not found.  This error is set by @code{gdbm_delete}
(@pxref{Delete}) and @code{gdbm_fetch} (@pxref{Fetch}) when the requested
@var{key} value is not found in the database.

@kwindex GDBM_REORGANIZE_FAILED
@item GDBM_REORGANIZE_FAILED
The @code{gdbm_reorganize} function is not
able to create a temporary database.  @xref{Reorganization}.

@kwindex GDBM_CANNOT_REPLACE
@item GDBM_CANNOT_REPLACE
Cannot replace existing item.  This error is set by the
@code{gdbm_store} if the requested @var{key} value is found in the
database and the @var{flag} parameter is not @samp{GDBM_REPLACE}.
@xref{Store}, for a detailed discussion.

@kwindex GDBM_ILLEGAL_DATA
@item GDBM_ILLEGAL_DATA
Either @var{key} or @var{content} parameter was wrong in a call to
to @code{gdbm_store} (@pxref{Store}).

@kwindex GDBM_OPT_ALREADY_SET
@item GDBM_OPT_ALREADY_SET      
Requested option can be set only once and was already set.  This error
is returned by the @code{gdbm_setopt} function.  @xref{Options,
GDBM_CACHESIZE}.

@kwindex GDBM_OPT_ILLEGAL
@item GDBM_OPT_ILLEGAL
The @var{option} argument is not valid or the @var{value} argument
points to an invalid value in a call to @code{gdbm_setopt} function.
@xref{Options}.

@kwindex GDBM_BYTE_SWAPPED
@item GDBM_BYTE_SWAPPED
The @code{gdbm_open} function (@pxref{Open}) attempts to open a
database which is created on a machine with different byte ordering.

@kwindex GDBM_BAD_FILE_OFFSET
@item GDBM_BAD_FILE_OFFSET
The @code{gdbm_open} function (@pxref{Open}) sets this error code if
the file it tries to open has a wrong magic number.

@kwindex GDBM_BAD_OPEN_FLAGS
@item GDBM_BAD_OPEN_FLAGS
Set by the @code{gdbm_export} function if supplied an invalid
@var{flags} argument.  @xref{Flat files}.
@end table

@node Compatibility
@chapter Compatibility with standard @code{dbm} and @code{ndbm}.

GNU @code{dbm} files are not @code{sparse}.  You can copy them with the UNIX
@code{cp} command and they will not expand in the copying process.

There is a compatibility mode for use with programs that already use UNIX
@code{dbm} and UNIX @code{ndbm}.

GNU @code{dbm} has compatibility functions for @code{dbm}.  For @code{dbm}
compatibility functions, you need the include file @file{dbm.h}.

In this compatibility mode, no @code{gdbm} file pointer is required
by the user, and only one file may be opened at a time.  All users in
compatibility mode are assumed to be writers.  If the @code{gdbm} file is a
read only one, it will fail as a writer, but the library will try to open it
as a reader.  All returned pointers in datum structures point to data
that @code{gdbm} @emph{will} free.  They should be treated as static
pointers (as standard UNIX @code{dbm} does).  The compatibility
function names are the same as the UNIX @code{dbm} function
names.  Their definitions follow:

@example
int     dbminit (char *file);
datum   fetch (datum key);
int     store (datum key, datum content);
int     delete (datum key);
datum   firstkey (void);
datum   nextkey (datum key);
int     dbmclose (void);
@end example

Standard UNIX @code{dbm} and GNU @code{dbm} do not have the same data
format in the file.  You cannot access a standard UNIX @code{dbm} file
with GNU @code{dbm}!

Also, GNU @code{dbm} has compatibility functions for @code{ndbm}.  For
@code{ndbm} compatibility functions, you need the include file @code{ndbm.h}.

Again, just like @code{ndbm}, any returned datum can be assumed to be static
storage.  You do not have to free that memory, the @code{ndbm} compatibility
functions will do it for you.

The functions are:

@example
DBM     *dbm_open (char *file, int flags, int mode);
void     dbm_close (DBM *dbf);
datum    dbm_fetch (DBM *dbf, datum key);
int      dbm_store (DBM *dbf, datum key, datum content, int flags);
int      dbm_delete (DBM *dbf, datum key);
datum    dbm_firstkey (DBM *dbf);
datum    dbm_nextkey (DBM *dbf);
int dbm_error(DBM *dbf);
void dbm_clearerr(DBM *dbf)
int      dbm_dirfno (DBM *dbf);
int      dbm_pagfno (DBM *dbf);
int      dbm_rdonly (DBM *dbf);
@end example

If you want to compile an old C program that used UNIX @code{dbm} or
@code{ndbm} and want to use @code{gdbm} files, execute the following
@code{cc} command:

@example
cc ... -L/usr/local/lib -lgdbm -lgdbm_compat
@end example

@node Bugs
@chapter Problems and bugs.

If you have problems with GNU @code{dbm} or think you've found a bug,
please report it.  Before reporting a bug, make sure you've actually
found a real bug.  Carefully reread the documentation and see if it
really says you can do what you're trying to do.  If it's not clear
whether you should be able to do something or not, report that too; it's
a bug in the documentation!

Before reporting a bug or trying to fix it yourself, try to isolate it
to the smallest possible input file that reproduces the problem.  Then
send us the input file and the exact results @code{gdbm} gave you.  Also
say what you expected to occur; this will help us decide whether the
problem was really in the documentation.

Once you've got a precise problem, send e-mail to
@email{bug-gdbm@@gnu.org}.

Please include the version number of GNU @code{dbm} you are using.  You can get
this information by printing the variable @code{gdbm_version}
(@pxref{Variables}).

Non-bug suggestions are always welcome as well.  If you have questions
about things that are unclear in the documentation or are just obscure
features, please report them too.

You may contact the authors and maintainers by e-mail:
@example
@email{phil@@cs.wwu.edu}, @email{downsj@@downsj.com}, @email{gray@@gnu.org.ua}
@end example

@node GNU Free Documentation License
@appendix GNU Free Documentation License

@include fdl.texi

@node Index
@unnumbered Index

@printindex cp

@bye

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