gtk2/docs/faq/gtk-faq.sgml

<!doctype book PUBLIC "-//OASIS//DTD DocBook V3.1//EN" []>
<book>

<bookinfo>
  <date>February 27th 2001</date>
  <title>GTK+ FAQ</title>
  <authorgroup>
    <author>
<firstname>Tony</firstname>
<surname>Gale</surname>
    </author>
    <author>
<firstname>Shawn</firstname>
<surname>Amundson</surname>
    </author>
    <author>
<firstname>Emmanuel</firstname>
<surname>Deloget</surname>
    </author>
  </authorgroup>
  <abstract>
    <para> This document is intended to answer questions that are
    likely to be frequently asked by programmers using GTK+ or
    people who are just looking at using GTK+. </para>
  </abstract>
</bookinfo>

<toc></toc>

<!-- ***************************************************************** -->
<chapter>
<title>General Information</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Before anything else: the greetings</title>
<para>The FAQ authors want to thank:</para>
<itemizedlist spacing=Compact>
<listitem>
<simpara>Havoc Pennington</simpara>
</listitem>
<listitem>
<simpara>Erik Mouw</simpara>
</listitem>
<listitem>
<simpara>Owen Taylor</simpara>
</listitem>
<listitem>
<simpara>Tim Janik</simpara>
</listitem>
<listitem>
<simpara>Thomas Mailund Jensen</simpara>
</listitem>
<listitem>
<simpara>Joe Pfeiffer</simpara>
</listitem>
<listitem>
<simpara>Andy Kahn</simpara>
</listitem>
<listitem>
<simpara>Federico Mena Quntero</simpara>
</listitem>
<listitem>
<simpara>Damon Chaplin</simpara>
</listitem>
<listitem>
<simpara>and all the members of the GTK+ lists</simpara>
</listitem></itemizedlist>
<para> If we forgot you, please email us! Thanks again (I know,
it's really short :) </para>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Authors</title>

<para>The original authors of GTK+ were:</para>

<itemizedlist spacing=Compact>
<listitem>
<simpara>Peter Mattis</simpara>
</listitem>
<listitem>
<simpara>Spencer Kimball</simpara>
</listitem>
<listitem>
<simpara>Josh MacDonald</simpara>
</listitem>
</itemizedlist>

<para>Since then, much has been added by others. Please see the
AUTHORS file in the distribution for the GTK+ Team.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What is GTK+?</title>

<para>GTK+ is a small and efficient widget set designed with
the general look and feel of Motif.  In reality, it looks much
better than Motif.  It contains common widgets and some more
complex widgets such as a file selection, and color selection
widgets.</para>

<para>GTK+ provides some unique features. (At least, I know of
no other widget library which provides them). For example, a
button does not contain a label, it contains a child widget,
which in most instances will be a label.  However, the child
widget can also be a pixmap, image or any combination possible
the programmer desires. This flexibility is adhered to
throughout the library.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What is the + in GTK+?</title>

<para>Peter Mattis informed the gtk mailing list that:</para>

<para><quote>I originally wrote gtk which included the three
libraries, libglib, libgdk and libgtk. It featured a flat
widget hierarchy. That is, you couldn't derive a new widget
from an existing one. And it contained a more standard
callback mechanism instead of the signal mechanism now present
in gtk+. The + was added to distinguish between the original
version of gtk and the new version. You can think of it as
being an enhancement to the original gtk that adds object
oriented features.</quote></para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Does the G in GTK+, GDK and GLib stand for?</title>

<para>GTK+ == Gimp Toolkit</para>
<para>GDK == GTK+ Drawing Kit</para>
<para>GLib == G Libray</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Where is the documentation for GTK+?</title>

<para>In the GTK+ distribution's doc/ directory you will find
the reference material for both GTK and GDK, this FAQ and the
GTK Tutorial.</para>

<para>In addition, you can find links to HTML versions of
these documents  by going to <ulink url="http://www.gtk.org/">
http://www.gtk.org/</ulink>. A
packaged version of the GTK Tutorial, with SGML, HTML,
Postscript, DVI and text versions can be found in <ulink
url="ftp://ftp.gtk.org/pub/gtk/tutorial">
ftp://ftp.gtk.org/pub/gtk/tutorial
</ulink></para>

<para>There are now a couple of books available that deal with
programming GTK+, GDK and GNOME:</para>

<itemizedlist>
<listitem><simpara>Eric Harlows book entitled "Developing
Linux Applications with GTK+ and GDK". The ISBN is
0-7357-0021-4</simpara>
</listitem>
<listitem><simpara>The example code from Eric's book is
available on-line at <ulink
url="http://www.bcpl.net/~eharlow/book">
http://www.bcpl.net/~eharlow/book</ulink></simpara>
</listitem>
<listitem><simpara>Havoc Pennington has released a book called
"GTK+/GNOME Application Development". The ISBN is
0-7357-0078-8</simpara>
<simpara>The free version of the book lives here: <ulink
url="http://developer.gnome.org/doc/GGAD/">
http://developer.gnome.org/doc/GGAD/
</ulink></simpara>
<simpara>And Havoc maintains information about it and
errata here: <ulink
url="http://pobox.com/~hp/gnome-app-devel.html">
http://pobox.com/~hp/gnome-app-devel.html
</ulink></simpara>
</listitem>
</itemizedlist>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Is there a mailing list (or mailing list archive) for
GTK+?</title>

<para>Information on mailing lists relating to GTK+ can be
found at: <ulink
url="http://www.gtk.org/mailinglists.html">
http://www.gtk.org/mailinglists.html
</ulink></para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How to get help with GTK+</title>

<para>First, make sure your question isn't answered in the
documentation, this FAQ or the tutorial. Done that? You're
sure you've done that, right? In that case, the best place to
post questions is to the GTK+ mailing list.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How to report bugs in GTK+</title>

<para>Bugs should be reported to the GNOME bug tracking system
(<ulink url="http://bugzilla.gnome.org">http://bugzilla.gnome.org</ulink>).
You will need to enter your email address and receive a password before
you can use the system to register a new bug report.</para>

<para>There are a number of options to select and boxes to fill in when
submitting a bug report. Please remember that the more information you
give, the easier it will be to track the problem down. Extra information
that may prove useful includes:</para>

<itemizedlist>
<listitem><simpara> How to reproduce the bug.</simpara>
<simpara>If you can reproduce it with the testgtk program
that is built in the gtk/ subdirectory, that will be most
convenient. Otherwise, please include a short test program
that exhibits the behavior. As a last resort, you can also
provide a pointer to a larger piece of software that can
be downloaded.</simpara>
<simpara>(Bugs that can be reproduced within the GIMP are
almost as good as bugs that can be reproduced in
testgtk. If you are reporting a bug found with the GIMP,
please include the version number of the GIMP you are
using)</simpara>
</listitem>

<listitem><simpara> If the bug was a crash, the exact text that was
printed out when the crash occurred.</simpara>
</listitem>

<listitem><simpara> Further information such as stack traces
may be useful, but are not necessary. If you do send a stack trace,
and the error is an X error, it will be more useful if the stacktrace is
produced running the test program with the <literal>--sync</literal>
command line option.</simpara>
</listitem>
</itemizedlist>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Is there a Windows version of GTK+?</title>

<para>There is an on going port of GTK+ to the Windows
platform which is making impressive progress.</para>

<para>See <ulink
url="http://www.iki.fi/tml/gimp/win32">
http://www.iki.fi/tml/gimp/win32</ulink>
for more information.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What applications have been written with GTK+?</title>

<para>A list of some GTK+ based application can be found on
the GTK+ web server at <ulink
url="http://www.gtk.org/apps/">http://www.gtk.org/apps/</ulink>
and contains more than 350 applications.</para>

<para>Failing that, look for a project to work on for the
GNOME project, <ulink
url="http://www.gnome.org/">http://www.gnome.org/</ulink>
Write a game. Write something that is useful.</para>
<para>Some of these are:</para>

<itemizedlist>
<listitem><simpara> GIMP (<ulink
url="http://www.gimp.org/">http://www.gimp.org/</ulink>), an
image manipulation program</simpara>
</listitem>
<listitem><simpara> AbiWord (<ulink
url="http://www.abisource.com/">http://www.abisource.com/</ulink>),
a professional word processor</simpara>
</listitem>
<listitem><simpara> Gzilla (<ulink
url="http://www.levien.com/gzilla/">http://www.levien.com/gzilla/</ulink>),
a web browser</simpara>
</listitem>
<listitem><simpara> XQF (<ulink
url="http://www.botik.ru/~roma/quake/">
http://www.botik.ru/~roma/quake/</ulink>),
a QuakeWorld/Quake2 server browser and launcher</simpara>
</listitem>
<listitem><simpara> GDK Imlib (<ulink
url="http://www.rasterman.com/imlib.html">
http://www.rasterman.com/imlib.html</ulink>),
a fast image loading and manipulation library for GDK</simpara>
</listitem>
<listitem><simpara> Glade (<ulink
url="http://glade.pn.org/">http://glade.pn.org/</ulink>), a
GTK+ based RAD tool which produces GTK+ applications</simpara>
</listitem>
</itemizedlist>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I'm looking for an application to write in GTK+. How
about an IRC client?</title>

<para>Ask on gtk-list for suggestions. There are at least
three IRC clients already under development (probably more in fact. The
server at <ulink url="http://www.forcix.cx/irc-clients.html">
http://www.forcix.cx/irc-clients.html</ulink> list a bunch of
them).</para>

<itemizedlist spacing=compact>
<listitem><simpara> X-Chat.</simpara>
</listitem>
<listitem><simpara> girc. (Included with GNOME)</simpara>
</listitem>
<listitem><simpara> gsirc. (In the gnome CVS tree)</simpara>
</listitem>
</itemizedlist>

</sect1>

</chapter>

<!-- ***************************************************************** -->
<chapter>
<title>How to find, configure, install, and troubleshoot GTK+</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What do I need to run GTK+?</title>

<para>To compile GTK+, all you need is a C compiler (gcc) and
the X Window System and associated libraries on your system.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Where can I get GTK+?</title>

<para>The canonical site is <ulink
url="ftp://ftp.gtk.org/pub/gtk">ftp://ftp.gtk.org/pub/gtk</ulink>.</para>

<para>This site tends to get busy around the time of a new
GTK+ release so try and use one of the mirror sites that are
listed in <ulink
url="ftp://ftp.gtk.org/etc/mirrors">ftp://ftp.gtk.org/etc/mirrors
</ulink></para>

<para>Here's a few mirror sites to get you started:</para>

<itemizedlist spacing=compact>
<listitem><simpara> Africa -
<ulink url="ftp://ftp.is.co.za/applications/gimp">
ftp://ftp.is.co.za/applications/gimp</ulink></simpara> 
</listitem>
<listitem><simpara> Australia -
<ulink
url="ftp://ftp.au.gimp.org/pub/gimp">
ftp://ftp.au.gimp.org/pub/gimp</ulink></simpara> 
</listitem>
<listitem><simpara> Finland -
<ulink url="ftp://ftp.funet.fi/pub/sci/graphics/packages/gimp">
ftp://ftp.funet.fi/pub/sci/graphics/packages/gimp</ulink></simpara> 
</listitem>
<listitem><simpara> Germany -
<ulink url="ftp://infosoc.uni-koeln.de/pub/ftp.gimp.org">
ftp://infosoc.uni-koeln.de/pub/ftp.gimp.org"</ulink></simpara> 
</listitem>
<listitem><simpara> Japan -
<ulink url="ftp://SunSITE.sut.ac.jp/pub/archives/packages/gimp">
ftp://SunSITE.sut.ac.jp/pub/archives/packages/gimp</ulink></simpara> 
</listitem>
<listitem><simpara> UK - 
<ulink url="ftp://ftp.flirble.org/pub/X/gimp">
ftp://ftp.flirble.org/pub/X/gimp</ulink></simpara>
</listitem>
<listitem><simpara> US -
<ulink url="ftp://ftp.insync.net/pub/mirrors/ftp.gimp.org">
ftp://ftp.insync.net/pub/mirrors/ftp.gimp.org</ulink></simpara> 
</listitem>
</itemizedlist>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I configure/compile GTK+?</title>

<para>Generally, all you will need to do is issue the commands:</para>

<para><literallayout><literal>./configure</literal>
<literal>make</literal></literallayout></para>

<para>in the gtk+-version/ directory.</para>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>When compiling GTK+ I get an error like: <literal>make:
file `Makefile' line 456: Syntax error</literal></title>

<para>Make sure that you are using GNU make
(use <literal>make -v</literal>
to check). There are many weird and wonderful versions of make
out there, and not all of them handle the automatically
generated Makefiles.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I've compiled and installed GTK+, but I can't get any
programs to link with it!</title>

<para>This problem is most often encountered when the GTK+
libraries can't be  found or are the wrong version. Generally,
the compiler will complain about an 'unresolved symbol'.
There are two things you need to check:</para>

<itemizedlist>
<listitem><simpara>Make sure that the libraries can be
found. You want to edit <filename>/etc/ld.so.conf</filename> to
include the directories which contain the GTK libraries,
so it looks something like:</simpara>

<para><literallayout><literal>/usr/X11R6/lib</literal>
<literal>/usr/local/lib</literal></literallayout></para>

<para>Then you need to run /sbin/ldconfig as root. You can
find what directory GTK is in using</para>

<para><literallayout><literal>gtk-config --libs</literal>
</literallayout></para>

<para>If your system doesn't use ld.so to find libraries
(such as Solaris), then you will have to use the LD_LIBRARY_PATH
environment variable (or compile the path into your program, which I'm
not going to cover here). So, with a Bourne type shell you can do (if
your GTK libraries are in /usr/local/lib):</para>

<para><literallayout>
<literal>export LD_LIBRARY_PATH=/usr/local/lib</literal>
</literallayout></para>

<para>and in a csh, you can do:</para>

<para><literallayout>
<literal>setenv LD_LIBRARY_PATH /usr/local/lib</literal>
</literallayout></para>

</listitem>
<listitem><simpara>Make sure the linker is finding the
correct set of libraries. If you have a Linux distribution that
installs GTK+ (e.g. RedHat 5.0) then this  older version may be
used. Now (assuming you have a RedHat system), issue the
command</simpara>

<para><literallayout>
<literal>rpm -e gtk gtk-devel</literal>
</literallayout></para>

<para>You may also want to remove the packages that depend
on gtk (rpm will tell you which ones they are).  If you don't have a
RedHat Linux system, check to make sure that neither
<filename>/usr/lib</filename> or <filename>/usr/local/lib</filename>
contain any of the libraries libgtk, libgdk, libglib, or libgck. If
they do exist, remove them (and any gtk include files, such as
<filename>/usr/include/gtk</filename> and
<filename>/usr/include/gdk</filename>) and reinstall gtk+.</para>
</listitem>
</itemizedlist>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>When compiling programs with GTK+, I get compiler error
messages about not being able to find
<literal>glibconfig.h</literal>.</title>

<para>The header file "glibconfig.h" was moved to the
directory $exec_prefix/lib/glib/include/. $exec_prefix is the
directory that was specified by giving the --exec-prefix flags
to ./configure when compiling GTK+. It defaults to  $prefix,
(specified with --prefix), which in turn defaults to /usr/local/.</para>

<para>This was done because "glibconfig.h" includes
architecture dependent information, and the rest of the
include files are put in $prefix/include, which can be shared
between different architectures.</para>

<para>GTK+ includes a shell script, <literal>/gtk-config/</literal>,
that makes it easy to find out the correct include paths. The GTK+
Tutorial includes an example of using <literal>/gtk-config/</literal>
for simple compilation from the command line. For information about more
complicated configuration, see the file docs/gtk-config.txt in the GTK+
distribution.</para>

<para>If you are trying to compile an old program, you may be
able to work around the problem by configuring it with a
command line like:</para>

<para><literallayout>
<literal>setenv CPPFLAGS "-I/usr/local/include/glib/include"</literal>
<literal>./configure</literal>
</literallayout></para>

<para>(Substitute the appropriate value of $exec_prefix for
/usr/local.)</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>When installing a GTK+ application, configure reports
that it can't find GTK.</title>

<para>There are several common reasons for this:</para>

<itemizedlist>
<listitem><simpara>You have an old version of GTK installed
somewhere. RedHat 5.0, for example, installs an older copy of GTK that
may not work with the latest applications. You should remove this old
copy, but note that in the case of RedHat 5.0 this will
break the <literal>control-panel</literal> applications.</simpara>
</listitem>

<listitem><simpara><literal>gtk-config</literal> (or another
component of GTK) isn't in your path, or there is an old
version on your system. Type:</simpara>

<para><literallayout>
<literal>gtk-config --version</literal>
</literallayout></para>

<para>to check for both of these. If it returns a value
different from what you expect, then you have an old
version of GTK on your system.</para>
</listitem>

<listitem><simpara>The ./configure script can't find the GTK
libraries. As ./configure compiles various test programs, it needs to be
able to find the GTK libraries. See the question above
for help on this. </simpara></listitem>
</itemizedlist>

<para>If none of the above help, then have a look in
config.log, which is generated by ./configure as it runs. At the
bottom will be the last action it took before failing. If it is a
section of source code, copy the source code to a file and compile it
with the line just above it in config.log. If the compilation is
successful, try executing it.</para>

</sect1>

</chapter>

<!-- ***************************************************************** -->
<chapter>
<title>Development of GTK+</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Whats this CVS thing that everyone keeps talking about,
and how do I access it?</title>

<para>CVS is the Concurent Version System and is a very
popular means of version control for software projects. It is
designed to allow multiple  authors to be able to
simultanously operate on the same source tree.  This source
tree is centrally maintained, but each developer has a local
mirror of this repository that they make there changes to.</para>

<para>The GTK+ developers use a CVS repository to store the
master copy of the current development version of GTK+. As
such, people wishing to contribute patches to GTK+ should
generate them against the CVS version. Normal people should
use the packaged releases.</para>

<para>The CVS toolset is available as RPM packages from the
usual RedHat sites. The latest version is available at <ulink
url="http://download.cyclic.com/pub/">http://download.cyclic.com/pub/
</ulink></para>

<para>Anyone can download the latest CVS version of GTK+ by
using anonymous access using the following steps:</para>

<itemizedlist>
<listitem><simpara> In a bourne shell descendant (e.g. bash) type:</simpara>
<para><literallayout>
<literal>CVSROOT=':pserver:anonymous@anoncvs.gnome.org:/cvs/gnome'</literal>
<literal>export CVSROOT</literal>
</literallayout></para>
</listitem>

<listitem><simpara>Next, the first time the source tree is
checked out, a cvs login is needed. </simpara>
<para><literallayout>
<literal>cvs login</literal>
</literallayout></para>
<para>This will ask you for a password. There is no
password for cvs.gimp.org, so just enter a carriage return.</para>
</listitem>

<listitem><simpara>To get the tree and place it in a subdir of your
current working directory, issue the command:</simpara>
<para><literallayout>
<literal>cvs -z3 get gtk+</literal>
</literallayout></para>
<para>Note that with the GTK+ 1.1 tree, glib has been moved to
a separate CVS module, so if you don't have glib installed you will
need to get that as well:</para>
<para><literallayout>
<literal>cvs -z3 get glib</literal>
</literallayout></para>
</listitem>
</itemizedlist>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How can I contribute to GTK+?</title>

<para>It's simple. If something doesn't work like you think it
should in a program, check the documentation to make sure
you're not missing something. If it is a true bug or missing
feature, track it down in the GTK+ source, change it,  and
then generate a patch in the form of a 'context diff'. This
can be done using a command such as <literal>diff -ru
&lt;oldfile&gt; &lt;newfile&gt;</literal>. Then upload the patchfile
to:</para>

<para><literallayout>
<literal>ftp://ftp.gtk.org/incoming</literal>
</literallayout></para>

<para>along with a README file. Make sure you follow the
naming conventions or your patch will just be deleted! The
filenames should be of this form:</para>

<para><literallayout>
<literal>gtk&lt;username&gt;-&lt;date yymmdd-n&gt;.patch.gz</literal>
<literal>gtk-&lt;username&gt;-&lt;date yymmdd-n&gt;.patch.README</literal>
</literallayout></para>

<para>The "n" in the date indicates a unique number (starting
from 0) of patches you uploaded that day.  It should be 0,
unless you upload more than one patch in the same day.</para>

<para>Example:</para>

<para><literallayout>
<literal>gtk-gale-982701-0.patch.gz</literal>
<literal>gtk-gale-982701-0.patch.README</literal>
</literallayout></para>

<para>Once you upload <emphasis>anything</emphasis>, send the README to
ftp-admin@gtk.org</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I know if my patch got applied, and if not, why
not?</title>

<para>Uploaded patches will be moved to
<filename>ftp://ftp.gtk.org/pub/gtk/patches</filename> where one of the
GTK+ development team will pick them up. If applied, they will be moved
to <filename>/pub/gtk/patches/old</filename>.</para>

<para>Patches that aren't applied, for whatever reason, are
moved to <filename>/pub/gtk/patches/unapplied</filename> or
<filename>/pub/gtk/patches/outdated</filename>. At this point you can ask
on the <literal>gtk-list</literal> mailing list why your patch wasn't
applied. There are many possible reasons why patches may not
be applied, ranging from it doesn't apply cleanly, to it isn't
right. Don't be put off if your patch didn't make it first
time round.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What is the policy on incorporating new widgets into
the library?</title>

<para>This is up to the authors, so you will have to ask them
once you are done with your widget. As a general guideline,
widgets that are  generally useful, work, and are not a
disgrace to the widget set will gladly be included.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Is anyone working on bindings for languages other than
C?</title>

<para>The GTK+ home page (<ulink
url="http://www.gtk.org/">http://www.gtk.org/</ulink>)
presents a list of GTK+ bindings.</para>

<itemizedlist>
<listitem><simpara>There are several C++ wrappers for GTK+.</simpara>

  <itemizedlist> 
  <listitem><simpara>the gtk-- package, which is a very small wrapper for
  GTK+. You can find the home page at <ulink
  url="http://www.cs.tut.fi/~p150650/gtk/gtk--.html">
  http://www.cs.tut.fi/~p150650/gtk/gtk--.html</ulink>. The FTP site is 
  <ulink url="ftp://ftp.gtk.org/pub/gtk/gtk--">
  ftp://ftp.gtk.org/pub/gtk/gtk--</ulink>.</simpara>
  </listitem>

  <listitem><simpara>the VDK package, which was built as
  the base package of a GTK+ application Borland-like
  builder. The home page can be found at <ulink
  url="http://www.guest.net/homepages/mmotta/VDKHome">
  http://www.guest.net/homepages/mmotta/VDKHome</ulink>.</simpara>
  </listitem>

  <listitem><simpara>The wxWindows/Gtk package, a free C++ library for
  cross-platform GUI development. The home page of this package is
  <ulink url="http://www.freiburg.linux.de/~wxxt/">
  http://www.freiburg.linux.de/~wxxt/</ulink>.</simpara>
  </listitem>

  </itemizedlist>
</listitem>

<listitem><simpara>There are three known Objective-c
bindings currently in development:</simpara>

  <itemizedlist> 
  <listitem><simpara>The <ulink
  url="http://www.gnome.org/">http://www.gnome.org/</ulink>
  package of choice is objgtk. Objgtk is based on the Object class and
  is maintained by <ulink url="mailto:sopwith@cuc.edu">Elliot
  Lee</ulink>. Apparently, objgtk is being accepted as the `standard'
  Objective-C binding for GTK+.</simpara>
  </listitem>

  <listitem><simpara>If you are more inclined towards the 
  <ulink url="http://www.gnustep.org/">GNUstep project</ulink>,
  you may want to check out GTKKit by 
  <ulink url="mailto:helge@mdlink.de">Helge He&szlig;</ulink>.
  The intention is to setup a GTK+ binding using the FoundationKit. 
  GTKKit includes nicities like writing a XML-type template file to 
  construct a GTK+ interface.</simpara>
  </listitem>

  <listitem><simpara>The GToolKit package, which can be found at
  <ulink url="ftp://ftp.gtk.org/pub/gtk/objc-gtoolkit/">
  ftp://ftp.gtk.org/pub/gtk/objc-gtoolkit/</ulink>.</simpara>
  </listitem>
  
  </itemizedlist>
</listitem>

<listitem><simpara>Perl bindings <ulink
url="ftp://ftp.gtk.org/pub/gtk/perl">
ftp://ftp.gtk.org/pub/gtk/perl</ulink></simpara>
</listitem>

<listitem><simpara>Guile bindings. The home page is at
<ulink url="http://www.ping.de/sites/zagadka/guile-gtk">
http://www.ping.de/sites/zagadka/guile-gtk</ulink>.
By the way, Guile is the GNU Project's implemention of R4RS Scheme (the
standard). If you like Scheme, you may want to take a look at
this.</simpara>
</listitem>

<listitem><simpara>David Monniaux reports:
<quote>I've started a gtk-O'Caml binding system.
The basics of the system, including callbacks, work fine.

The current development is in
<ulink url="http://www.ens-lyon.fr/~dmonniau/arcs">
http://www.ens-lyon.fr/~dmonniau/arcs</ulink>
</quote></simpara>
</listitem>

<listitem><simpara>Several python bindings have been done:</simpara>

  <itemizedlist>
  <listitem><simpara>pygtk is at 
  <ulink url="http://www.daa.com.au/~james/pygtk">
  http://www.daa.com.au/~james/pygtk</ulink> and 
  <ulink url="ftp://ftp.gtk.org/pub/gtk/python">
  ftp://ftp.gtk.org/pub/gtk/python</ulink></simpara>
  </listitem>

  <listitem><simpara>python-gtk is at
  <ulink url="http://www.ucalgary.ca/~nascheme/python-gtk">
  http://www.ucalgary.ca/~nascheme/python-gtk</ulink></simpara>
  </listitem>
  
  </itemizedlist>
</listitem>

<listitem><simpara>There's are a couple of OpenGL/Mesa
widgets available for GTK+. I suggest you start at
<ulink url="http://www.student.oulu.fi/~jlof/gtkglarea/index.html">
http://www.student.oulu.fi/~jlof/gtkglarea/index.html</ulink></simpara>
</listitem>
<listitem><simpara>Last, there are a lot of other language
bindings for languages such as Eiffel, TOM, Pascal, Pike, etc.</simpara>
</listitem>

</itemizedlist>
</sect1>

</chapter>

<!-- ***************************************************************** -->
<chapter>
<title>Development with GTK+: the begining</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I get started?</title>

<para>So, after you have installed GTK+ there are a couple of
things that can ease you into developing applications with
it. There is the GTK+ Tutorial <ulink
url="http://www.gtk.org/tutorial/">
http://www.gtk.org/tutorial/</ulink>, which is undergoing
development. This will introduce you to writing applications
using C.</para>

<para>The Tutorial doesn't (yet) contain information on all of
the widgets that are in GTK+. For example code on how to use
the basics of all the GTK+ widgets you should look at the file
gtk/testgtk.c (and associated source files) within the GTK+
distribution. Looking at these examples will give you a good
grounding on what the widgets can do.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I write security sensitive/SUID/SGID programs with GTK+?
Is GTK+ secure? What's this GTK_MODULES security hole I heard about?</title>

<para>The short answer to this question is: Don't write SUID/SGID
programs with GTK+</para>

<para>For a more thorough explanation of the GTK+ Developers position on
this issue see <ulink
url="http://www.gtk.org/setuid.html">http://www.gtk.org/setuid.html</ulink>.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I tried to compile a small <command>Hello World</command> of mine,
but it failed. Any clue?</title>

<para>Since you are good at coding, we will not deal with
compile time error here :)</para>

<para>The classic command line to compile a GTK+ based program is</para>
<para><literallayout>
<literal>gcc -o myprog [c files] `gtk-config --cflags --libs`</literal>
</literallayout></para>

<para>You should notice the backquote character which is used
in this command line. A common mistake when you start a GTK+
based development is to use quote instead of backquotes. If
you do so, the compiler will complain about an unknown file
called <filename>gtk-config --cflags --libs</filename>. The
text in backquotes is an instruction to your shell to
substitute the output of executing this text into the
commandline.</para>

<para>The command line above ensure that:</para>

<itemizedlist>
<listitem><simpara>the correct C compiler flags will be used
to compile the program (including the complete C header
directory list)</simpara>
</listitem>

<listitem><simpara>your program will be linked with the
needed libraries.</simpara>
</listitem>
</itemizedlist>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What about using the <command>make</command>
utility?</title>

<para>This is a sample makefile which compile a GTK+ based
program:</para>

<programlisting role="C">
# basic GTK+ app makefile
SOURCES = myprg.c foo.c bar.c
OBJS    = ${SOURCES:.c=.o}
CFLAGS  = `gtk-config --cflags`
LDADD   = `gtk-config --libs`
CC      = gcc
PACKAGE = myprg

all : ${OBJS}
  ${CC} -o ${PACKAGE} ${OBJS} ${LDADD}

.c.o:
  ${CC} ${CFLAGS} -c $<

# end of file
</programlisting>

<para>For more information about the <command>make</command> utility, you
should read either the related man page or the relevant info file.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I use the backquote stuff in my makefiles, but my make
process failed.</title>

<para>The backquote construction seems to not be accepted by
some old <command>make</command> utilities. If you use one of these, the
make process will probably fail. In order to have the
backquote syntax working again, you should use the GNU make
utility (get it on the GNU ftp server at <ulink
url="ftp://ftp.gnu.org/">ftp://ftp.gnu.org/</ulink>).</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I want to add some configure stuff, how could I do
this?</title>

<para>To use autoconf/automake, you must first install the
relevant packages. These are:</para>

<itemizedlist spacing=Compact>
<listitem><simpara>the m4 preprocessor v1.4 or better</simpara>
</listitem>

<listitem><simpara>autoconf v2.13 or better</simpara>
</listitem>

<listitem><simpara>automake v1.4 or better</simpara>
</listitem>
</itemizedlist>

<para>You'll find these packages on the GNU main ftp server
(<ulink url="ftp://ftp.gnu.org/">ftp://ftp.gnu.org/</ulink>)
or on any GNU mirror.</para>

<para>In order to use the powerful autoconf/automake scheme,
you must create a configure.in which may look like:</para>

<programlisting role="C">
dnl Process this file with autoconf to produce a configure script.
dnl configure.in for a GTK+ based program

AC_INIT(myprg.c)dnl
AM_INIT_AUTOMAKE(mypkgname,0.0.1)dnl
AM_CONFIG_HEADER(config.h)dnl

dnl Checks for programs.
AC_PROG_CC dnl check for the c compiler
dnl you should add CFLAGS="" here, 'cos it is set to -g by PROG_CC

dnl Checks for libraries.
AM_PATH_GTK(1.2.0,,AC_MSG_ERROR(mypkgname 0.1 needs GTK))dnl

AC_OUTPUT(
	Makefile
)dnl
</programlisting>

<para>You must add a Makefile.am file:</para>

<programlisting role="C">
bin_PROGRAMS    = myprg
myprg_SOURCES   = myprg.c foo.c bar.c
INCLUDES        = @GTK_CFLAGS@
LDADD           = @GTK_LIBS@
CLEANFILES      = *~
DISTCLEANFILES  = .deps/*.P
</programlisting>

<para>If your project contains more than one subdirectory,
you'll have to create one Makefile.am in each directory plus a
master Makefile.am which will look like:</para>

<programlisting role="C">
SUBDIRS         = mydir1 mydir2 mydir3
</programlisting>

<para>then, to use these, simply type the following
commands:</para>

<programlisting role="C">
aclocal
autoheader
autoconf
automake --add-missing --include-deps --foreign 
</programlisting>

<para>For further information, you should look at the autoconf
and the automake documentation (the shipped info files are
really easy to understand, and there are plenty of web
resources that deal with autoconf and automake).</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I try to debug my GTK+ application with gdb, but it
hangs my X server when I hit some breakpoint. Any
Idea?</title>

<para>From Federico Mena Quintero:</para>

<para><quote>X is not locked up.  It is likely that you are hitting a
breakpoint inside a callback that is called from a place in Gtk that has
a mouse grab.</quote></para>

<para><quote>Run your program with the <literal>--sync</literal>
option; it will make it easier to debug. Also, you may want to
use the console for running the debugger, and just let the
program run in another console with the X server.</quote></para>

<para>Eric Mouw had another solution:</para>

<para><quote>An old terminal connected to an otherwise unused serial
port is also great for debugging X programs. Old vt100/vt220
terminals are dirt cheap but a bit hard to get (here in The
Netherlands, YMMV).</quote></para>

</sect1>
</chapter>

<!-- ***************************************************************** -->
<chapter>
<title>Development with GTK+: general questions</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What widgets are in GTK?</title>

<para>The GTK+ Tutorial lists the following widgets:</para>

<programlisting role="C">
  GtkObject
   +GtkData
   | +GtkAdjustment
   | `GtkTooltips
   `GtkWidget
     +GtkContainer
     | +GtkBin
     | | +GtkAlignment
     | | +GtkEventBox
     | | +GtkFrame
     | | | `GtkAspectFrame
     | | +GtkHandleBox
     | | +GtkItem
     | | | +GtkListItem
     | | | +GtkMenuItem
     | | | | `GtkCheckMenuItem
     | | | |   `GtkRadioMenuItem
     | | | `GtkTreeItem
     | | +GtkViewport
     | | `GtkWindow
     | |   +GtkColorSelectionDialog
     | |   +GtkDialog
     | |   | `GtkInputDialog
     | |   `GtkFileSelection
     | +GtkBox
     | | +GtkButtonBox
     | | | +GtkHButtonBox
     | | | `GtkVButtonBox
     | | +GtkHBox
     | | | +GtkCombo
     | | | `GtkStatusbar
     | | `GtkVBox
     | |   +GtkColorSelection
     | |   `GtkGammaCurve
     | +GtkButton
     | | +GtkOptionMenu
     | | `GtkToggleButton
     | |   `GtkCheckButton
     | |     `GtkRadioButton
     | +GtkCList
     |   `GtkCTree
     | +GtkFixed
     | +GtkList
     | +GtkMenuShell
     | | +GtkMenuBar
     | | `GtkMenu
     | +GtkNotebook
     | +GtkPaned
     | | +GtkHPaned
     | | `GtkVPaned
     | +GtkScrolledWindow
     | +GtkTable
     | +GtkToolbar
     | `GtkTree
     +GtkDrawingArea
     | `GtkCurve
     +GtkEditable
     | +GtkEntry
     | | `GtkSpinButton
     | `GtkText
     +GtkMisc
     | +GtkArrow
     | +GtkImage
     | +GtkLabel
     | | `GtkTipsQuery
     | `GtkPixmap
     +GtkPreview
     +GtkProgressBar
     +GtkRange
     | +GtkScale
     | | +GtkHScale
     | | `GtkVScale
     | `GtkScrollbar
     |   +GtkHScrollbar
     |   `GtkVScrollbar
     +GtkRuler
     | +GtkHRuler
     | `GtkVRuler
     `GtkSeparator
       +GtkHSeparator
       `GtkVSeparator
</programlisting>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Is GTK+ thread safe? How do I write multi-threaded GTK+
applications?</title>

<para>The GLib library can be used in a thread-safe mode by
calling g_thread_init() before making any other GLib
calls. In this mode GLib automatically locks all internal
data structures as needed.  This does not mean that two
threads can simultaneously access, for example, a single hash
table, but they can access two different hash tables
simultaneously. If two different threads need to access the
same hash table, the application is responsible for locking
itself.</para>

<para>When GLib is intialized to be thread-safe, GTK+ is
<emphasis>thread aware</emphasis>. There is a single global
lock that you must acquire with gdk_threads_enter() before
making any GDK calls, and release with gdk_threads_leave()
afterwards.</para>

<para>A minimal main program for a threaded GTK+ application
looks like:</para>

<programlisting role="C">
int
main (int argc, char *argv[])
{
  GtkWidget *window;

  g_thread_init(NULL);
  gtk_init(&amp;argc, &amp;argv);

  window = create_window();
  gtk_widget_show(window);

  gdk_threads_enter();
  gtk_main();
  gdk_threads_leave();

  return(0);
}
</programlisting>

<para>Callbacks require a bit of attention. Callbacks from
GTK+ (signals) are made within the GTK+ lock. However
callbacks from GLib (timeouts, IO callbacks, and idle
functions) are made outside of the GTK+ lock. So, within a
signal handler you do not need to call gdk_threads_enter(),
but within the other types of callbacks, you do.</para>

<para>Erik Mouw contributed the following code example to
illustrate how to use threads within GTK+ programs.</para>

<programlisting role="C">
/*-------------------------------------------------------------------------
 * Filename:      gtk-thread.c
 * Version:       0.99.1
 * Copyright:     Copyright (C) 1999, Erik Mouw
 * Author:        Erik Mouw &lt;J.A.K.Mouw@its.tudelft.nl&gt;
 * Description:   GTK threads example. 
 * Created at:    Sun Oct 17 21:27:09 1999
 * Modified by:   Erik Mouw &lt;J.A.K.Mouw@its.tudelft.nl&gt;
 * Modified at:   Sun Oct 24 17:21:41 1999
 *-----------------------------------------------------------------------*/
/*
 * Compile with:
 *
 * cc -o gtk-thread gtk-thread.c `gtk-config --cflags --libs gthread`
 *
 * Thanks to Sebastian Wilhelmi and Owen Taylor for pointing out some
 * bugs.
 *
 */

#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;unistd.h&gt;
#include &lt;time.h&gt;
#include &lt;gtk/gtk.h&gt;
#include &lt;glib.h&gt;
#include &lt;pthread.h&gt;

#define YES_IT_IS    (1)
#define NO_IT_IS_NOT (0)

typedef struct 
{
  GtkWidget *label;
  int what;
} yes_or_no_args;

G_LOCK_DEFINE_STATIC (yes_or_no);
static volatile int yes_or_no = YES_IT_IS;

void destroy(GtkWidget *widget, gpointer data)
{
  gtk_main_quit();
}

void *argument_thread(void *args)
{
  yes_or_no_args *data = (yes_or_no_args *)args;
  gboolean say_something;

  for(;;)
    {
      /* sleep a while */
      sleep(rand() / (RAND_MAX / 3) + 1);

      /* lock the yes_or_no_variable */
      G_LOCK(yes_or_no);

      /* do we have to say something? */
      say_something = (yes_or_no != data->what);

      if(say_something)
	{
	  /* set the variable */
	  yes_or_no = data->what;
	}

      /* Unlock the yes_or_no variable */
      G_UNLOCK(yes_or_no);

      if(say_something)
	{
	  /* get GTK thread lock */
	  gdk_threads_enter();

	  /* set label text */
	  if(data->what == YES_IT_IS)
	    gtk_label_set_text(GTK_LABEL(data->label), "O yes, it is!");
	  else
	    gtk_label_set_text(GTK_LABEL(data->label), "O no, it isn't!");

	  /* release GTK thread lock */
	  gdk_threads_leave();
	}
    }

  return(NULL);
}

int main(int argc, char *argv[])
{
  GtkWidget *window;
  GtkWidget *label;
  yes_or_no_args yes_args, no_args;
  pthread_t no_tid, yes_tid;

  /* init threads */
  g_thread_init(NULL);

  /* init gtk */
  gtk_init(&amp;argc, &amp;argv);

  /* init random number generator */
  srand((unsigned int)time(NULL));

  /* create a window */
  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

  gtk_signal_connect(GTK_OBJECT (window), "destroy",
		     GTK_SIGNAL_FUNC(destroy), NULL);

  gtk_container_set_border_width(GTK_CONTAINER (window), 10);

  /* create a label */
  label = gtk_label_new("And now for something completely different ...");
  gtk_container_add(GTK_CONTAINER(window), label);
  
  /* show everything */
  gtk_widget_show(label);
  gtk_widget_show (window);

  /* create the threads */
  yes_args.label = label;
  yes_args.what = YES_IT_IS;
  pthread_create(&amp;yes_tid, NULL, argument_thread, &amp;yes_args);

  no_args.label = label;
  no_args.what = NO_IT_IS_NOT;
  pthread_create(&amp;no_tid, NULL, argument_thread, &amp;no_args);

  /* enter the GTK main loop */
  gdk_threads_enter();
  gtk_main();
  gdk_threads_leave();

  return(0);
}
</programlisting>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Why does this strange 'x io error' occur when I
<literal>fork()</literal> in my GTK+ app?</title>

<para>This is not really a GTK+ problem, and the problem is
not related to <literal>fork()</literal> either. If the 'x io
error' occurs then you probably use the <literal>exit()</literal> function
in order to exit from the child process.</para>

<para>When GDK opens an X display, it creates a socket file
descriptor. When you use the <literal>exit()</literal>
function, you implicitly close all the open file descriptors,
and the underlying X library really doesn't like this.</para>

<para>The right function to use here is
<literal>_exit()</literal>.</para> 

<para>Erik Mouw contributed the following code example to
illustrate handling fork() and exit().</para>

<programlisting role="C">
/*-------------------------------------------------------------------------
 * Filename:      gtk-fork.c
 * Version:       0.99.1
 * Copyright:     Copyright (C) 1999, Erik Mouw
 * Author:        Erik Mouw &lt;J.A.K.Mouw@its.tudelft.nl&gt;
 * Description:   GTK+ fork example
 * Created at:    Thu Sep 23 21:37:55 1999
 * Modified by:   Erik Mouw &lt;J.A.K.Mouw@its.tudelft.nl&gt;
 * Modified at:   Thu Sep 23 22:39:39 1999
 *-----------------------------------------------------------------------*/
/*
 * Compile with:
 *
 * cc -o gtk-fork gtk-fork.c `gtk-config --cflags --libs`
 *
 */

#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;signal.h&gt;
#include &lt;sys/types.h&gt;
#include &lt;sys/wait.h&gt;
#include &lt;unistd.h&gt;
#include &lt;gtk/gtk.h&gt;

void sigchld_handler(int num)
{
  sigset_t set, oldset;
  pid_t pid;
  int status, exitstatus;

  /* block other incoming SIGCHLD signals */
  sigemptyset(&amp;set);
  sigaddset(&amp;set, SIGCHLD);
  sigprocmask(SIG_BLOCK, &amp;set, &amp;oldset);

  /* wait for child */
  while((pid = waitpid((pid_t)-1, &amp;status, WNOHANG)) > 0)
    {
      if(WIFEXITED(status))
	{
	  exitstatus = WEXITSTATUS(status);

	  fprintf(stderr, 
		  "Parent: child exited, pid = %d, exit status = %d\n", 
		  (int)pid, exitstatus);
	}
      else if(WIFSIGNALED(status))
	{
	  exitstatus = WTERMSIG(status);

	  fprintf(stderr,
		  "Parent: child terminated by signal %d, pid = %d\n",
		  exitstatus, (int)pid);
	}
      else if(WIFSTOPPED(status))
	{
	  exitstatus = WSTOPSIG(status);

	  fprintf(stderr,
		  "Parent: child stopped by signal %d, pid = %d\n",
		  exitstatus, (int)pid);
	}
      else
	{
	  fprintf(stderr,
		  "Parent: child exited magically, pid = %d\n",
		  (int)pid);
	}
    }

  /* re-install the signal handler (some systems need this) */
  signal(SIGCHLD, sigchld_handler);
  
  /* and unblock it */
  sigemptyset(&amp;set);
  sigaddset(&amp;set, SIGCHLD);
  sigprocmask(SIG_UNBLOCK, &amp;set, &amp;oldset);
}

gint delete_event(GtkWidget *widget, GdkEvent *event, gpointer data)
{
  return(FALSE);
}

void destroy(GtkWidget *widget, gpointer data)
{
  gtk_main_quit();
}

void fork_me(GtkWidget *widget, gpointer data)
{
  pid_t pid;

  pid = fork();

  if(pid == -1)
    {
      /* ouch, fork() failed */
      perror("fork");
      exit(-1);
    }
  else if(pid == 0)
    {
      /* child */
      fprintf(stderr, "Child: pid = %d\n", (int)getpid());

      execlp("ls", "ls", "-CF", "/", NULL);
      
      /* if exec() returns, there is something wrong */
      perror("execlp");

      /* exit child. note the use of _exit() instead of exit() */
      _exit(-1);
    }
  else
    {
      /* parent */
      fprintf(stderr, "Parent: forked a child with pid = %d\n", (int)pid);
    }
}

int main(int argc, char *argv[])
{
  GtkWidget *window;
  GtkWidget *button;

  gtk_init(&amp;argc, &amp;argv);

  /* the basic stuff: make a window and set callbacks for destroy and
   * delete events 
   */
  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

  gtk_signal_connect(GTK_OBJECT (window), "delete_event",
		     GTK_SIGNAL_FUNC(delete_event), NULL);
          
  gtk_signal_connect(GTK_OBJECT (window), "destroy",
		     GTK_SIGNAL_FUNC(destroy), NULL);

#if (GTK_MAJOR_VERSION == 1) && (GTK_MINOR_VERSION == 0)
  gtk_container_border_width(GTK_CONTAINER (window), 10);
#else  
  gtk_container_set_border_width(GTK_CONTAINER (window), 10);
#endif

  /* add a button to do something usefull */
  button = gtk_button_new_with_label("Fork me!");
          
  gtk_signal_connect(GTK_OBJECT (button), "clicked",
		     GTK_SIGNAL_FUNC(fork_me), NULL);

  gtk_container_add(GTK_CONTAINER(window), button);
          
  /* show everything */
  gtk_widget_show (button);
  gtk_widget_show (window);


  /* install a signal handler for SIGCHLD signals */
  signal(SIGCHLD, sigchld_handler);

  
  /* main loop */
  gtk_main ();

  exit(0);         
}
</programlisting>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Why don't the contents of a button move when the button
is pressed? Here's a patch to make it work that way...</title>

<para>From: Peter Mattis</para>

<para><quote>The reason buttons don't move their child down and to
the right when they are depressed is because I don't think
that's what is happening visually. My view of buttons is
that you are looking at them straight on. That is, the user
interface lies in a plane and you're above it looking
straight at it. When a button gets pressed it moves directly
away from you. To be absolutely correct I guess the child
should actually shrink a tiny amount. But I don't see why
the child should shift down and to the left. Remember, the
child is supposed to be attached to the buttons surface. Its
not good for it to appear like the child is slipping on the
surface of the button.</quote></para>

<para><quote>On a more practical note, I did implement this at one point
and determined it didn't look good and removed it.</quote></para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I identifiy a widgets top level window or other
ancestor?</title>

<para>There are a couple of ways to find the top level parent
of a widget. The easier way is to call the
<literal>gtk_widget_top_level()</literal> function that
returns pointer to a GtkWidget that is the top level
window.</para>

<para>A more complicated way to do this (but less limited, as
it allows the user to get the closest ancestor of a known type) is to use
<literal>gtk_widget_get_ancestor()</literal> as in:</para>

<programlisting role="C">
      GtkWidget       *widget;
      widget = gtk_widget_get_ancestor(w, GTK_TYPE_WINDOW);
</programlisting>

<para>Since virtually all the GTK_TYPEs can be used as the
second parameter of this function, you can get any parent
widget of a particular widget. Suppose you have an hbox which
contains a vbox, which in turn contains some other atomic
widget (entry, label, etc. To find the master hbox using the
<literal>entry</literal> widget simply use:</para>

<programlisting role="C">
      GtkWidget       *hbox;
      hbox = gtk_widget_get_ancestor(w, GTK_TYPE_HBOX);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I get the Window ID of a GtkWindow?</title>

<para>The actual Gdk/X window will be created when the widget
gets realized. You can get the Window ID with:</para>

<programlisting role="C">
#include &lt;gdk/gdkx.h&gt;

Window xwin = GDK_WINDOW_XWINDOW (GTK_WIDGET (my_window)->window);
</programlisting>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I catch a double click event (in a list widget,
for example)?</title>

<para>Tim Janik wrote to gtk-list (slightly modified):</para>

<para>Define a signal handler:</para>

<programlisting role="C">
gint
signal_handler_event(GtkWidget *widget, GdkEventButton *event, gpointer func_data)
{
  if (GTK_IS_LIST_ITEM(widget) &&
       (event->type==GDK_2BUTTON_PRESS ||
        event->type==GDK_3BUTTON_PRESS) ) {
    printf("I feel %s clicked on button %d\n",
           event->type==GDK_2BUTTON_PRESS ? "double" : "triple",
           event->button);
  }

  return FALSE;
}</programlisting>

<para>And connect the handler to your object:</para>

<programlisting role="C">
{
  /* list, list item init stuff */     

  gtk_signal_connect(GTK_OBJECT(list_item),
                     "button_press_event",
                     GTK_SIGNAL_FUNC(signal_handler_event),
                     NULL);

  /* and/or */

  gtk_signal_connect(GTK_OBJECT(list_item),
                     "button_release_event",
                     GTK_SIGNAL_FUNC(signal_handler_event),
                     NULL);

  /* something else */
}
</programlisting>

<para>and, Owen Taylor wrote:</para>

<para><quote>Note that a single button press will be received
beforehand, and if you are doing this for a button, you will
therefore also get a "clicked" signal for the button. (This
is going to be true for any toolkit, since computers aren't
good at reading one's mind.)</quote></para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>By the way, what are the differences between signals
and events?</title>

<para>First of all, Havoc Pennington gives a rather complete
description of the differences between events and signals in
his free book (two chapters can be found at <ulink
url="http://www106.pair.com/rhp/sample_chapters.html">
http://www106.pair.com/rhp/sample_chapters.html</ulink>).</para>

<para>Moreover, Havoc posted this to the <literal>gtk-list</literal>
<quote>Events are a stream of messages received from the X
server. They drive the Gtk main loop; which more or less
amounts to "wait for events, process them" (not exactly, it
is really more general than that and can wait on many
different input streams at once). Events are a Gdk/Xlib
concept.</quote></para>

<para><quote>Signals are a feature of GtkObject and its subclasses. They
have nothing to do with any input stream; really a signal is just a way
to keep a list of callbacks around and invoke them ("emit" the
signal). There are lots of details and extra features of
course. Signals are emitted by object instances, and are entirely
unrelated to the Gtk main loop.  Conventionally, signals are emitted
"when something changes" about the object emitting the
signal.</quote></para>

<para><quote>Signals and events only come together because GtkWidget
happens to emit signals when it gets events. This is purely a
convenience, so you can connect callbacks to be invoked when a
particular widget receives a particular event. There is nothing about
this that makes signals and events inherently related concepts, any more
than emitting a signal when you click a button makes button clicking and
signals related concepts.</quote></para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Data I pass to the <literal>delete_event</literal> (or other event)
handler gets corrupted.</title>

<para>All event handlers take an additional argument which
contains information about the event that triggered the
handler. So, a <literal>delete_event</literal> handler must
be declared as:</para>


<programlisting role="C">
gint delete_event_handler (GtkWidget   *widget,
                           GdkEventAny *event,
                           gpointer     data);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I have my signal connected to the the (whatever) event,
but it seems I don't catch it. What's wrong?</title>

<para>There is some special initialisation to do in order to
catch some particular events. In fact, you must set the
correct event mask bit of your widget before getting some
particular events.</para>

<para>For example,</para>

<programlisting role="C">
  gtk_widget_add_events(window, GDK_KEY_RELEASE_MASK);
</programlisting>

<para>lets you catch the key release events. If you want to
catch every events, simply us the GDK_ALL_EVENTS_MASK event
mask.</para>

<para>All the event masks are defined in the
<filename>gdktypes.h</filename> file.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I need to add a new signal to a GTK+ widget. Any
idea?</title>

<para>If the signal you want to add may be beneficial for
other GTK+ users, you may want to submit a patch that
presents your changes. Check the tutorial for more
information about adding signals to a widget class.</para>

<para>If you don't think it is the case or if your patch is
not applied you'll have to use the
<literal>gtk_object_class_user_signal_new</literal>
function. <literal>gtk_object_class_user_signal_new</literal> allows you
to add a new signal to a predefined GTK+ widget without any
modification of the GTK+ source code. The new signal can be
emited with <literal>gtk_signal_emit</literal> and can be
handled in the same way as other signals.</para>

<para>Tim Janik posted this code snippet:</para>

<programlisting role="C">
static guint signal_user_action = 0;

signal_user_action =
  gtk_object_class_user_signal_new (gtk_type_class (GTK_TYPE_WIDGET),
                    "user_action",
                    GTK_RUN_LAST | GTK_RUN_ACTION,
                    gtk_marshal_NONE__POINTER,
                    GTK_TYPE_NONE, 1,
                    GTK_TYPE_POINTER);

void
gtk_widget_user_action (GtkWidget *widget,
                        gpointer   act_data)
{
  g_return_if_fail (GTK_IS_WIDGET (widget));

  gtk_signal_emit (GTK_OBJECT (widget), signal_user_action, act_data);
}
</programlisting>

<para>If you want your new signal to have more than the
classical gpointer parameter, you'll have to play with GTK+
marshallers.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Is it possible to get some text displayed which is
truncated to fit inside its allocation?</title>

<para>GTK's behavior (no clipping) is a consequence of its
attempts to conserve X resources. Label widgets (among
others) don't get their own X window - they just draw their
contents on their parent's window. While it might be possible
to have clipping occur by setting the clip mask before
drawing the text, this would probably cause a substantial
performance penalty.</para>

<para>Its possible that, in the long term, the best solution
to such problems might be just to change gtk to give labels X
windows. A short term workaround is to put the label widget
inside another widget that does get its own window - one
possible candidate would be the viewport widget.</para>

<programlisting role="C">
viewport = gtk_viewport (NULL, NULL);
gtk_widget_set_usize (viewport, 50, 25);
gtk_viewport_set_shadow_type (GTK_VIEWPORT(viewport), GTK_SHADOW_NONE);
gtk_widget_show(viewport);

label = gtk_label ("a really long label that won't fit");
gtk_container_add (GTK_CONTAINER(viewport), label);
gtk_widget_show (label);
</programlisting>

<para>If you were doing this for a bunch of widgets, you might
want to copy gtkviewport.c and strip out the adjustment and
shadow functionality (perhaps you could call it
GtkClipper).</para>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I make my window modal? / How do I make a single
window active?</title>

<para>After you create your window, do
<literal>gtk_grab_add(my_window)</literal>. And after closing the window
do <literal>gtk_grab_remove(my_window)</literal>.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Why doesn't my widget (e.g. progressbar)
update?</title>

<para>You are probably doing all the changes within a function without
returning control to <literal>gtk_main()</literal>. This may
be the case if you do some lengthy calculation in your
code. Most drawing updates are only placed on a queue, which
is processed within <literal>gtk_main()</literal>. You can force the
drawing queue to be processed using something like:</para>


<programlisting role="C">
while (g_main_iteration(FALSE));
</programlisting>

<para>inside you're function that changes the widget.</para>

<para>What the above snippet does is run all pending events
and high priority idle functions, then return immediately
(the drawing is done in a high priority idle function).</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I attach data to some GTK+ object/widget?</title>

<para>First of all, the attached data is stored in the
object_data field of a GtkObject. The type of this field is
GData, which is defined in glib.h.  So you should read the
gdataset.c file in your glib source directory very
carefully.</para>

<para>There are two (easy) ways to attach some data to a gtk
object.  Using <literal>gtk_object_set_data()</literal> and
<literal>gtk_object_get_data()</literal> seems to be the most
common way to do this, as it provides a powerful interface to
connect objects and data.</para>

<programlisting role="C">
void gtk_object_set_data(GtkObject *object, const gchar *key, gpointer data);

gpointer gtk_object_get_data(GtkObject *object, const gchar *key);
</programlisting>

<para>Since a short example is better than any lengthy speech:</para>

<programlisting role="C">
struct my_struct	p1,p2,*result;
GtkWidget		*w;

gtk_object_set_data(GTK_OBJECT(w),"p1 data",(gpointer)&amp;p1);
gtk_object_set_data(GTK_OBJECT(w),"p2 data",(gpointer)&amp;p2);

result = gtk_object_get_data(GTK_OBJECT(w),"p1 data");
</programlisting>

<para>The <literal>gtk_object_set_user_data()</literal> and
<literal>gtk_object_get_user_data()</literal> functions does
exactly the same thing as the functions above, but does not
let you specify the "key" parameter.Instead, it uses a
standard "user_data" key. Note that the use of these functions
is deprecated in 1.2. They only provide a compatibility mode
with some old gtk packages.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I remove the data I have attached to an
object?</title>

<para>When attaching the data to the object, you can use the
<literal>gtk_object_set_data_full()</literal> function. The three
first arguments of the function are the same as in
<literal>gtk_object_set_data()</literal>. The fourth one is a
pointer to a callback function which is called when the data
is destroyed. The data is destroyed when you:</para>

<itemizedlist>
<listitem><simpara> destroy the object</simpara>
</listitem>

<listitem><simpara> replace the data with a new one (with
the same key)</simpara>
</listitem>

<listitem><simpara> replace the data with NULL (with the
same key)</simpara>
</listitem>

</itemizedlist>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I reparent a widget?</title>

<para>The normal way to reparent (ie change the owner) of a
widget should be to use the function:</para>

<programlisting role="C">
void gtk_widget_reparent (GtkWidget *widget, 
                          GtkWidget *new_parent)
</programlisting>

<para>But this is only a "should be" since this function does
not correctly do its job on some specific widgets. The main
goal of gtk_widget_reparent() is to avoid unrealizing widget
if both widget and new_parent are realized (in this case,
widget->window is successfully reparented). The problem here
is that some widgets in the GTK+ hierarchy have multiple
attached X subwindows and this is notably the case for the
GtkSpinButton widget. For those, gtk_widget_reparent() will
fail by leaving an unrealized child window where it should
not.</para>

<para>To avoid this problem, simply use the following code
snippet:</para>

<programlisting role="C">
     gtk_widget_ref(widget);
     gtk_container_remove(GTK_CONTAINER(old_parent), widget);
     gtk_container_add(GTK_CONTAINER(new_parent), widget);
     gtk_widget_unref(widget);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How could I get any widgets position?</title>

<para>As Tim Janik pointed out, there are different cases, and
each case requires a different solution.</para>

<itemizedlist>
<listitem><simpara> If you want the position of a widget
relative to its parent, you should use
<literal>widget->allocation.x</literal> and
<literal>widget->allocation.y</literal>.</simpara>
</listitem>

<listitem><simpara> If you want the position of a window
relative to the X root window, you should use
<literal>gdk_window_get_geometry()</literal>
<literal>gdk_window_get_position()</literal> or
<literal>gdk_window_get_origin()</literal>.</simpara>
</listitem>

<listitem><simpara> If you want to get the position of the
window (including the WM decorations), you should use
<literal>gdk_window_get_root_origin()</literal>.</simpara>
</listitem>

<listitem><simpara> Last but not least, if you want to get a Window
Manager frame position, you should use
<literal>gdk_window_get_deskrelative_origin()</literal>.</simpara>
</listitem>
</itemizedlist>

<para>Your choice of Window Manager will have an effect of the
results of the above functions. You should keep this in mind
when writing your application. This is dependant upon how the
Window Managers manage the decorations that they add around
windows.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I set the size of a widget/window? How do I
prevent the user resizing my window?</title>

<para>The <literal>gtk_widget_set_uposition()</literal>
function is used to set the position of any widget.</para>

<para>The <literal>gtk_widget_set_usize()</literal> function
is used to set the size of a widget. In order to use all the
features that are provided by this function when it acts on a
window, you may want to use the
<literal>gtk_window_set_policy</literal> function. The
definition of these functions are:</para>

<programlisting role="C">
void gtk_widget_set_usize (GtkWidget *widget,
                           gint width,
                           gint height);

void gtk_window_set_policy (GtkWindow *window,
                            gint allow_shrink,
                            gint allow_grow,
                            gint auto_shrink);
</programlisting>

<para><literal>Auto_shrink</literal> will automatically shrink
the window when the requested size of the child widgets goes
below the current size of the
window. <literal>Allow_shrink</literal> will give the user the
authorisation to make the window smaller that it should
normally be. <literal>Allow_grow</literal> will give the user
will have the ability to make the window bigger. The default
values for these parameters are:</para>

<programlisting role="C">
allow_shrink = FALSE
allow_grow   = TRUE
auto_shrink  = FALSE
</programlisting>

<para>The <literal>gtk_widget_set_usize()</literal> functions
is not the easiest way to set a window size since you cannot
decrease this window size with another call to this function
unless you call it twice, as in:</para>

<programlisting role="C">
     gtk_widget_set_usize(your_widget, -1, -1);
     gtk_widget_set_usize(your_widget, new_x_size, new_y_size);
</programlisting>

<para>Another way to set the size of and/or move a window is to use
the <literal>gdk_window_move_resize()</literal> function which
uses to work fine both to grow or to shrink the window:</para>

<programlisting role="C">
     gdk_window_move_resize(window->window, 
                            x_pos, y_pos, 
                            x_size, y_size);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I add a popup menu to my GTK+ application?</title>

<para>The <literal>menu</literal> example in the examples/menu
directory of the GTK+ distribution implements a popup menu
with this technique:</para>

<programlisting role="C">
static gint button_press (GtkWidget *widget, GdkEvent *event)
{

    if (event->type == GDK_BUTTON_PRESS) {
        GdkEventButton *bevent = (GdkEventButton *) event; 
        gtk_menu_popup (GTK_MENU(widget), NULL, NULL, NULL, NULL,
                        bevent->button, bevent->time);
        /* Tell calling code that we have handled this event; the buck
         * stops here. */
        return TRUE;
    }

    /* Tell calling code that we have not handled this event; pass it on. */
    return FALSE;
}
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I disable or enable a widget, such as a
button?</title>

<para>To disable (or to enable) a widget, use the
<literal>gtk_widget_set_sensitive()</literal> function. The
first parameter is you widget pointer. The second parameter is
a boolean value: when this value is TRUE, the widget is
enabled.</para>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Shouldn't the text argument in the gtk_clist_*
functions be declared const?</title>

<para>For example:</para>

<programlisting role="C">
gint gtk_clist_prepend (GtkCList *clist,
                        gchar    *text[]);
</programlisting>

<para>Answer: No, while a type "gchar*" (pointer to char) can
automatically be cast into "const gchar*" (pointer to const
char), this does not apply for "gchar *[]" (array of an
unspecified number of pointers to char) into "const gchar *[]"
(array of an unspecified number of pointers to const char).</para>

<para>The type qualifier "const" may be subject to automatic
casting, but in the array case, it is not the array itself
that needs the (const) qualified cast, but its members, thus
changing the whole type.</para>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I render pixels (image data) to the
screen?</title>

<para>There are several ways to approach this. The simplest
way is to use GdkRGB, see gdk/gdkrgb.h. You create an RGB
buffer, render to your RGB buffer, then use GdkRGB routines to
copy your RGB buffer to a drawing area or custom widget. The
book "GTK+/Gnome Application Development" gives some details;
GdkRGB is also documented in the GTK+ reference
documentation.</para>

<para>If you're writing a game or other graphics-intensive
application, you might consider a more elaborate
solution. OpenGL is the graphics standard that will let you
access hardware accelaration in future versions of XFree86; so
for maximum speed, you probably want to use OpenGL. A
GtkGLArea widget is available for using OpenGL with GTK+ (but
GtkGLArea does not come with GTK+ itself). There are also
several open source game libraries, such as ClanLib and Loki's
Simple DirectMedia Layer library (SDL).</para>

<para>You do NOT want to use
<literal>gdk_draw_point()</literal>, that will be extremely
slow.</para>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I create a pixmap without having my window being
realized/shown?</title>

<para>Functions such as
<literal>gdk_pixmap_create_from_xpm()</literal> require a
valid window as a parameter. During the initialisation phase
of an application, a valid window may not be available without
showing a window, which may be inappropriate. In order to
avoid this, a function such as
<literal>gdk_pixmap_colormap_create_from_xpm</literal> can be
used, as in:</para>

<programlisting role="C">
  char *pixfile = "foo.xpm";
  GtkWidget *top, *box, *pixw;
  GdkPixmap *pixmap, *pixmap_mask;

  top = gtk_window_new (GKT_WINDOW_TOPLEVEL);
  box = gtk_hbox_new (FALSE, 4);
  gtk_conainer_add (GTK_CONTAINER(top), box);
 
  pixmap = gdk_pixmap_colormap_create_from_xpm (
               NULL, gtk_widget_get_colormap(top),
               &amp;pixmap_mask, NULL, pixfile);
  pixw = gtk_pixmap_new (pixmap, pixmap_mask);
  gdk_pixmap_unref (pixmap);
  gdk_pixmap_unref (pixmap_mask);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I do drag-and-drop?</title>

<para>GTK+ has a high level set of functions for doing inter-process
communication via the drag-and-drop system. GTK+ can perform
drag-and-drop on top of the low level Xdnd and Motif drag-and-drop
protocols.</para>

<para>The documentation on GTK+ drag-and-drop isn't complete, but there
is some information in the <ulink
url="http://www.gtk.org/tutorial/">Tutorial</ulink>. You should also
look at the drag-and-drop example code that is part of the GTK+ source
distribution, in the file <filename>gtk/testdnd.c</filename>.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Why does GTK+/GLib leak memory?</title>

<para>It doesn't. Both GLib and the C library (malloc implementation)
will cache allocated memory on occasion, even if you free it with
free().</para>

<para>So you can't generally use tools such as top to see if you are
using free() properly (aside from the very roughest of estimations, i.e.
if you are really, really screwing up top will show that, but you can't
distinguish small mistakes from the GLib/malloc caches).</para>

<para>In order to find memory leaks, use proper memory profiling
tools.</para>

</sect1>

</chapter>

<!-- ***************************************************************** -->
<chapter>
<title>Development with GTK+: widget specific questions</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I find out about the selection of a GtkList?</title>

<para>Get the selection something like this:</para>

<programlisting role="C">
GList *sel;
sel = GTK_LIST(list)->selection;
</programlisting>

<para>This is how GList is defined (quoting glist.h):</para>

<programlisting role="C">
typedef struct _GList GList;

struct _GList
{
  gpointer data;
  GList *next;
  GList *prev;
};
</programlisting>

<para>A GList structure is just a simple structure for doubly
linked lists. there exist several g_list_*() functions to
modify a linked list in glib.h.  However the
GTK_LIST(MyGtkList)->selection is maintained by the
gtk_list_*() functions and should not be modified.</para>


<para>The selection_mode of the GtkList determines the
selection facilities of a GtkList and therefore the contents
of GTK_LIST(AnyGtkList)->selection:</para>

<informaltable frame="all">
<tgroup cols="2">
<thead>
<row>
<entry><literal>selection_mode</literal></entry>
<entry><literal> GTK_LIST()->selection</literal>
contents</entry>
</row>
</thead>

<tbody>
<row>
<entry><literal>GTK_SELECTION_SINGLE</literal></entry>
<entry>selection is either NULL or contains a GList*
pointer for a single selected item.</entry>
</row>

<row>
<entry><literal>GTK_SELECTION_BROWSE</literal></entry>
<entry>selection is NULL if the list contains no
widgets, otherwise it contains a GList*
pointer for one GList structure.</entry>
</row>

<row>
<entry><literal>GTK_SELECTION_MULTIPLE</literal></entry>
<entry>selection is NULL if no listitems are selected
or a a GList* pointer for the first selected
item. that in turn points to a GList structure
for the second selected item and so
on.</entry>
</row>

<row>
<entry><literal>GTK_SELECTION_EXTENDED</literal></entry>
<entry>selection is NULL.</entry>
</row>

</tbody>
</tgroup>
</informaltable>

<para>The data field of the GList structure
GTK_LIST(MyGtkList)->selection points to the first
GtkListItem that is selected.  So if you would like to
determine which listitems are selected you should go like
this:</para>

<programlisting role="C">
{
        gchar           *list_items[]={
                                "Item0",
                                "Item1",
                                "foo",
                                "last Item",
                        };
        guint           nlist_items=sizeof(list_items)/sizeof(list_items[0]);
        GtkWidget       *list_item;
        guint           i;

        list=gtk_list_new();
        gtk_list_set_selection_mode(GTK_LIST(list), GTK_SELECTION_MULTIPLE);
        gtk_container_add(GTK_CONTAINER(AnyGtkContainer), list);
        gtk_widget_show (list);

        for (i = 0; i < nlist_items; i++)
        {
                list_item=gtk_list_item_new_with_label(list_items[i]);
                gtk_object_set_user_data(GTK_OBJECT(list_item), (gpointer)i);
                gtk_container_add(GTK_CONTAINER(list), list_item);
                gtk_widget_show(list_item);
        }
}
</programlisting>

<para>To get known about the selection:</para>

<programlisting role="C">
{
        GList   *items;

        items=GTK_LIST(list)->selection;

        printf("Selected Items: ");
        while (items) {
                if (GTK_IS_LIST_ITEM(items->data))
                        printf("%d ", (guint) 
                gtk_object_get_user_data(items->data));
                items=items->next;
        }
        printf("\n");
}
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I stop the column headings of a GtkCList
disappearing when the list is scrolled?</title>

<para>This happens when a GtkCList is packed into a
GtkScrolledWindow using the function
<literal>gtk_scroll_window_add_with_viewport()</literal>. The prefered
method of adding a CList to a scrolled window is to use the
function <literal>gtk_container_add</literal>, as in:</para>

<programlisting role="C">
    GtkWidget *scrolled, *clist;
    char *titles[] = { "Title1" , "Title2" };

    scrolled = gtk_scrolled_window_new(NULL, NULL);

    clist = gtk_clist_new_with_titles(2, titles);
    gtk_container_add(GTK_CONTAINER(scrolled), clist);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I don't want the user of my applications to enter text
into a GtkCombo. Any idea?</title>

<para>A GtkCombo has an associated entry which can be accessed
using the following expression:</para>

<programlisting role="C">
      GTK_COMBO(combo_widget)->entry
</programlisting>

<para>If you don't want the user to be able to modify the
content of this entry, you can use the
gtk_entry_set_editable() function:</para>


<programlisting role="C">
      void gtk_entry_set_editable(GtkEntry *entry, 
                                  gboolean editable);
</programlisting>

<para>Set the editable parameter to FALSE to disable typing
into the entry.</para>
</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I catch a combo box change?</title>

<para>The entry which is associated to your GtkCombo send a
"changed" signal when:</para>

<itemizedlist>
<listitem><simpara>some text is typed in</simpara>
</listitem>

<listitem><simpara>the selection of the combo box is changed</simpara>
</listitem>
</itemizedlist>

<para>To catch any combo box change, simply connect your
signal handler with</para>

<programlisting role="C">
      gtk_signal_connect(GTK_COMBO(cb)->entry,
                         "changed",
                         GTK_SIGNAL_FUNC(my_cb_change_handler),
                         NULL);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How can I define a separation line in a menu?</title>

<para>See the <ulink
url="http://www.gtk.org/tutorial/">Tutorial</ulink> for
information on how to create menus. However, to create a
separation line in a menu, just insert an empty menu item:</para>

<programlisting role="C">
menuitem = gtk_menu_item_new();
gtk_menu_append(GTK_MENU(menu), menuitem);
gtk_widget_show(menuitem);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How can I right justify a menu, such as Help?</title>

<para>Depending on if you use the MenuFactory or not, there
are two ways to proceed. With the MenuFactory, use something
like the following:</para>

<programlisting role="C">
menu_path = gtk_menu_factory_find (factory,  "&lt;MyApp&gt;/Help");
gtk_menu_item_right_justify(menu_path->widget);
</programlisting>

<para>If you do not use the MenuFactory, you should simply
use:</para>


<programlisting role="C">
gtk_menu_item_right_justify(my_menu_item);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I add some underlined accelerators to menu
items?</title>

<para>Damon Chaplin, the technical force behind the Glade
project, provided the following code sample (this code is an
output from Glade). It creates a small <GUIMenu>File</guimenu> menu item
with only one child (<guimenu>New</guimenu>). The F in
<guimenu>File</guimenu> and the N in <guimenu>New</guimenu> are
underlined, and the relevant accelerators are created.</para>

<programlisting role="C">
  menubar1 = gtk_menu_bar_new ();
  gtk_object_set_data (GTK_OBJECT (window1), "menubar1", menubar1);
  gtk_widget_show (menubar1);
  gtk_box_pack_start (GTK_BOX (vbox1), menubar1, FALSE, FALSE, 0);

  file1 = gtk_menu_item_new_with_label ("");
  tmp_key = gtk_label_parse_uline (GTK_LABEL (GTK_BIN (file1)->child),
                                   _("_File"));
  gtk_widget_add_accelerator (file1, "activate_item", accel_group,
                              tmp_key, GDK_MOD1_MASK, 0);
  gtk_object_set_data (GTK_OBJECT (window1), "file1", file1);
  gtk_widget_show (file1);
  gtk_container_add (GTK_CONTAINER (menubar1), file1);

  file1_menu = gtk_menu_new ();
  file1_menu_accels = gtk_menu_ensure_uline_accel_group (GTK_MENU (file1_menu));
  gtk_object_set_data (GTK_OBJECT (window1), "file1_menu", file1_menu);
  gtk_menu_item_set_submenu (GTK_MENU_ITEM (file1), file1_menu);

  new1 = gtk_menu_item_new_with_label ("");
  tmp_key = gtk_label_parse_uline (GTK_LABEL (GTK_BIN (new1)->child),
                                   _("_New"));
  gtk_widget_add_accelerator (new1, "activate_item", file1_menu_accels,
                              tmp_key, 0, 0);
  gtk_object_set_data (GTK_OBJECT (window1), "new1", new1);
  gtk_widget_show (new1);
  gtk_container_add (GTK_CONTAINER (file1_menu), new1);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How can I retrieve the text from a GtkMenuItem?</title>

<para>You can usually retrieve the label of a specific
GtkMenuItem with:</para>

<programlisting role="C">
    if (GTK_BIN (menu_item)->child)
    {
      GtkWidget *child = GTK_BIN (menu_item)->child;
  
      /* do stuff with child */
      if (GTK_IS_LABEL (child))
      {
        gchar *text;
    
        gtk_label_get (GTK_LABEL (child), &amp;text);
        g_print ("menu item text: %s\n", text);
      }
    }
</programlisting>

<para>To get the active menu item from a GtkOptionMenu you can
do:</para>

<programlisting role="C">
if (GTK_OPTION_MENU (option_menu)->menu_item)
{
  GtkWidget *menu_item = GTK_OPTION_MENU (option_menu)->menu_item;
}
</programlisting>

<para>But, there's a catch. For this specific case, you can
<emphasis>not</emphasis> get the label widget from
<literal>menu_item</literal> with the above code, because the
option menu reparents the menu_item's child temporarily to
display the currently active contents. So to retrive the child
of the currently active menu_item of an option menu, you'll
have to do:</para>

<programlisting role="C">
    if (GTK_BIN (option_menu)->child)
    {
      GtkWidget *child = GTK_BIN (option_menu)->child;

      /* do stuff with child */
    }
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I right (or otherwise) justify a
GtkLabel?</title>

<para>Are you sure you want to <emphasis>justify</emphasis>
the labels? The label class contains the
<literal>gtk_label_set_justify()</literal> function that is
used to control the justification of a multi-line
label.</para>

<para>What you probably want is to set the <emphasis>alignment</emphasis>
of the label, ie right align it, center it or left align
it. If you want to do this, you should use:</para>

<programlisting role="C">
void gtk_misc_set_alignment (GtkMisc *misc,
                             gfloat xalign,
                             gfloat yalign);
</programlisting>

<para>where the <literal>xalign</literal> and
<literal>yalign</literal> values are floats in
[0.00;1.00].</para>

<programlisting role="C">
GtkWidget       *label;

/* horizontal : left align, vertical : top */
gtk_misc_set_alignment(GTK_MISC(label), 0.0f, 0.0f);

/* horizontal : centered, vertical : centered */
gtk_misc_set_alignment(GTK_MISC(label), 0.5f, 0.5f);

/* horizontal : right align, vertical : bottom */
gtk_misc_set_alignment(GTK_MISC(label), 1.0f, 1.0f);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I set the background color of a GtkLabel
widget?</title>

<para>The Gtklabel widget is one of a few GTK+ widgets that
don't create their own window to render themselves
into. Instead, they draw themselves directly onto their
parents window.</para>

<para>This means that in order to set the background color for
a GtkLabel widget, you need to change the background color of
its parent, i.e. the object that you pack it into.</para>

</sect1> 

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I set the color and font of a GtkLabel using a
Resource File?</title>

<para>The widget name path constructed for a Label consists of
the widget names of its object hierarchy as well, e.g.</para>

<para><literallayout>
<literal>window (name: humphrey)</literal>
<literal>  hbox</literal>
<literal>     label (name: mylabel)</literal>
</literallayout></para>

<para>The widget path your pattern needs to match would be:
<literal>humphrey.GtkHBox.mylabel</literal></para>

<para>The resource file may look something like:</para>

<programlisting role="C">
style "title"
{
      fg[NORMAL] = {1.0, 0.0, 0.0}
      font = "-adobe-helvetica-bold-r-normal--*-140-*-*-*-*-*-*"
}
widget "*mylabel" style "title"
</programlisting>

<para>In your program, you would also need to give a name to
the Label widget, which can be done using:</para>

<programlisting role="C">
  label = gtk_label_new("Some Label Text");
  gtk_widget_set_name(label, "mylabel");
  gtk_widget_show(label);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I configure Tooltips in a Resource File?</title>

<para>The tooltip's window is named "gtk-tooltips",
GtkTooltips in itself is not a GtkWidget (though a GtkObject)
and as such is not attempted to match any widget styles.</para>

<para>So, you resource file should look something like:</para>

<programlisting role="C">
style "postie"
{
      bg[NORMAL] = {1.0, 1.0, 0.0}
}
widget "gtk-tooltips*" style "postie"
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>I can't add more than (something like) 2000 chars in a
GtkEntry. What's wrong?</title>

<para>There is now a known problem in the GtkEntry widget. In
the <literal>gtk_entry_insert_text()</literal> function, the
following lines limit the number of chars in the entry to
2047.</para>

<programlisting role="C">
  /* The algorithms here will work as long as, the text size (a
   * multiple of 2), fits into a guint16 but we specify a shorter
   * maximum length so that if the user pastes a very long text, there
   * is not a long hang from the slow X_LOCALE functions.  */

  if (entry->text_max_length == 0)
    max_length = 2047;
  else
    max_length = MIN (2047, entry->text_max_length);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I make a GtkEntry widget activate on pressing
the Return key?</title>

<para>The Entry widget emits an 'activate' signal when you
press return in it. Just attach to the activate signal on the
entry and do whatever you want to do. Typical code would
be:</para>

<programlisting role="C">
  entry = gtk_entry_new();
  gtk_signal_connect (GTK_OBJECT(entry), "activate",
                      GTK_SIGNAL_FUNC(entry_callback),
                      NULL);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I validate/limit/filter the input to a GtkEntry?</title>

<para>If you want to validate the text that a user enters into
a GtkEntry widget you can attach to the "insert_text" signal
of the entry, and modify the text within the callback
function. The example below forces all characters to
uppercase, and limits the range of characters to A-Z. Note
that the entry is cast to an object of type GtkEditable, from
which GtkEntry is derived.</para>

<programlisting role="C">
#include &lt;ctype.h&gt;
#include &lt;gtk/gtk.h&gt;

void insert_text_handler (GtkEntry    *entry,
                          const gchar *text,
                          gint         length,
                          gint        *position,
                          gpointer     data)
{
  GtkEditable *editable = GTK_EDITABLE(entry);
  int i, count=0;
  gchar *result = g_new (gchar, length);

  for (i=0; i < length; i++) {
    if (!isalpha(text[i]))
      continue;
    result[count++] = islower(text[i]) ? toupper(text[i]) : text[i];
  }
  
  if (count > 0) {
    gtk_signal_handler_block_by_func (GTK_OBJECT (editable),
				      GTK_SIGNAL_FUNC (insert_text_handler),
				      data);
    gtk_editable_insert_text (editable, result, count, position);
    gtk_signal_handler_unblock_by_func (GTK_OBJECT (editable),
					GTK_SIGNAL_FUNC (insert_text_handler),
					data);
  }
  gtk_signal_emit_stop_by_name (GTK_OBJECT (editable), "insert_text");
  
  g_free (result);
}

int main (int   argc,
          char *argv[])
{
  GtkWidget *window;
  GtkWidget *entry;
  
  gtk_init (&amp;argc, &amp;argv);
  
  /* create a new window */
  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
  gtk_window_set_title(GTK_WINDOW (window), "GTK Entry");
  gtk_signal_connect(GTK_OBJECT (window), "delete_event",
		     (GtkSignalFunc) gtk_exit, NULL);
  
  entry = gtk_entry_new();
  gtk_signal_connect(GTK_OBJECT(entry), "insert_text",
		     GTK_SIGNAL_FUNC(insert_text_handler),
		     NULL);
  gtk_container_add(GTK_CONTAINER (window), entry);
  gtk_widget_show(entry);
  
  gtk_widget_show(window);
  
  gtk_main();
  return(0);
}
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I use horizontal scrollbars with a GtkText widget?</title>

<para>The short answer is that you can't. The current version
of the GtkText widget does not support horizontal
scrolling. There is an intention to completely rewrite the
GtkText widget, at which time this limitation will be
removed.</para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I change the font of a GtkText widget?</title>

<para>There are a couple of ways of doing this. As GTK+ allows
the appearance of applications to be changed at run time using
resources you can use something like the following in the
appropriate file:</para>

<programlisting role="C">
style "text"
{
  font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"
}
</programlisting>

<para>Another way to do this is to load a font within your
program, and then use this in the functions for adding text to
the text widget. You can load a font using, for example:</para>

<programlisting role="C">
  GdkFont *font;
  font = gdk_font_load("-adobe-helvetica-medium-r-normal--*-140-*-*-*-*-*-*");
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I set the cursor position in a GtkText
object?</title>

<para>Notice that the response is valid for any object that
inherits from the GtkEditable class.</para>

<para>Are you sure that you want to move the cursor position?
Most of the time, while the cursor position is good, the
insertion point does not match the cursor position. If this
apply to what you really want, then you should use the
<literal>gtk_text_set_point()</literal> function. If you want
to set the insertion point at the current cursor position, use
the following:</para>

<programlisting role="C">
  gtk_text_set_point(GTK_TEXT(text),
  gtk_editable_get_position(GTK_EDITABLE(text)));
</programlisting>

<para>If you want the insertion point to follow the cursor at
all time, you should probably catch the button press event,
and then move the insertion point. Be careful : you'll have to
catch it after the widget has changed the cursor position
though. Thomas Mailund Jensen proposed the following
code:</para>

<programlisting role="C">
static void
insert_bar (GtkWidget *text)
{
  /* jump to cursor mark */
  gtk_text_set_point (GTK_TEXT (text),
  gtk_editable_get_position (GTK_EDITABLE  (text)));

  gtk_text_insert (GTK_TEXT (text), NULL, NULL, NULL,
     "bar", strlen ("bar"));
}

int
main (int argc, char *argv[])
{
  GtkWidget *window, *text;

  gtk_init (&amp;argc, &amp;argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  text = gtk_text_new (NULL, NULL);
  gtk_text_set_editable (GTK_TEXT (text), TRUE);
  gtk_container_add (GTK_CONTAINER (window), text);

  /* connect after everything else */
  gtk_signal_connect_after (GTK_OBJECT(text), "button_press_event",
    GTK_SIGNAL_FUNC (insert_bar), NULL);

  gtk_widget_show_all(window);
  gtk_main();

  return 0;
}
</programlisting>

<para>Now, if you really want to change the cursor position,
you should use the
<literal>gtk_editable_set_position()</literal>
function.</para>

</sect1>

</chapter>

<!-- ***************************************************************** -->
<chapter>
<title>About GDK</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What is GDK?</title>

<para>GDK is basically a wrapper around the standard Xlib
function calls. If you are at all familiar with Xlib, a lot of
the functions in GDK will require little or no getting used
to. All functions are written to provide an way to access Xlib
functions in an easier and slightly more intuitive manner. In
addition, since GDK uses GLib (see below), it will be more
portable and safer to use on multiple platforms.</para>

<!-- Examples, anybody? I've been mulling some over. NF -->

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How do I use color allocation?</title>

<para>One of the nice things about GDK is that it's based on
top of Xlib; this is also a problem, especially in the area of
color management. If you want  to use color in your program
(drawing a rectangle or such, your code  should look something
like this:</para>

<programlisting role="C">
{
  GdkColor *color;
  int width, height;
  GtkWidget *widget;
  GdkGC *gc;

  ...
  
  /* first, create a GC to draw on */
  gc = gdk_gc_new(widget->window);

  /* find proper dimensions for rectangle */
  gdk_window_get_size(widget->window, &amp;width, &amp;height);

  /* the color we want to use */
  color = (GdkColor *)malloc(sizeof(GdkColor));
  
  /* red, green, and blue are passed values, indicating the RGB triple
   * of the color we want to draw. Note that the values of the RGB components
   * within the GdkColor are taken from 0 to 65535, not 0 to 255.
   */
  color->red = red * (65535/255);
  color->green = green * (65535/255);
  color->blue = blue * (65535/255);
  
  /* the pixel value indicates the index in the colormap of the color.
   * it is simply a combination of the RGB values we set earlier
   */
  color->pixel = (gulong)(red*65536 + green*256 + blue);

  /* However, the pixel valule is only truly valid on 24-bit (TrueColor)
   * displays. Therefore, this call is required so that GDK and X can
   * give us the closest color available in the colormap
   */
  gdk_color_alloc(gtk_widget_get_colormap(widget), color);

  /* set the foreground to our color */
  gdk_gc_set_foreground(gc, color);
  
  /* draw the rectangle */
  gdk_draw_rectangle(widget->window, gc, 1, 0, 0, width, height);

  ...
}
</programlisting>

</sect1>

</chapter>

<!-- ***************************************************************** -->
<chapter>
<title>About GLib</title>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What is GLib?</title>

<para>GLib is a library of useful functions and definitions
available for use  when creating GDK and GTK applications. It
provides replacements for some standard libc functions, such
as malloc, which are buggy on some systems.</para>

<para>It also provides routines for handling:</para>

<itemizedlist spacing=compact>
<listitem><simpara>Doubly Linked Lists</simpara>
</listitem>

<listitem><simpara>Singly Linked Lists</simpara>
</listitem>

<listitem><simpara>Timers</simpara>
</listitem>

<listitem><simpara>String Handling</simpara>
</listitem>

<listitem><simpara>A Lexical Scanner</simpara>
</listitem>

<listitem><simpara>Error Functions</simpara>
</listitem>
</itemizedlist>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>How can I use the doubly linked lists?</title>

<para>The GList object is defined as:</para>

<programlisting role="C">
typedef struct _GList GList;

struct _GList
{
  gpointer data;
  GList *next;
  GList *prev;
};
</programlisting>

<para>To use the GList objects, simply:</para>

<programlisting role="C">
GList   *list = NULL;
GList   *listrunner;
gint    array[] = { 1, 2, 3, 4, 5, 6 };
gint    pos;
gint    *value;

/* add data to the list */
for (pos=0;pos < sizeof array; pos++) {
  list = g_list_append(list, (gpointer)&amp;array[pos]);
}

/* run through the list */
listrunner = g_list_first(list);
while (listrunner) {
  value = (gint *)listrunner->data;
  printf("%d\n", *value);
  listrunner = g_list_next(listrunner);
}

/* removing datas from the list */
listrunner = g_list_first(list);
list = g_list_remove_link(list, listrunner);
list = g_list_remove(list, &amp;array[4]);
</programlisting>

<para>The same code is usable with singly linked lists (GSList
objects) by replacing g_list_* functions with the relevant
g_slist_* ones (g_slist_append,  g_slist_remove, ...). Just
remember that since you can't go backward in a singly linked
list, there is no g_slist_first function - you'll need to keep
a  reference on the first node of the list.</para>

<!-- Some Examples might be useful here! NF -->
<!-- I believe it should be better :) ED -->
<!-- Linked lists are pretty standard data structures - don't want to
over do it - TRG -->

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Memory does not seem to be released when I free the
list nodes I've allocated</title>

<para>GLib tries to be "intelligent" on this special issue: it
assumes that you are likely to reuse the objects, so caches
the allocated memory. If you do not want to use this behavior,
you'll probably want to set up a special allocator.</para>

<para>To quote Tim Janik:</para>
<para><quote>If you have a certain portion of code that uses *lots*
of GLists or GNodes, and you know you'd better want to release
all of them after a short while, you'd want to use a
GAllocator. Pushing an allocator into g_list will make all
subsequent glist operations private to that allocator's memory
pool (and thus you have to take care to pop the allocator
again, before making any external calls): </quote></para>

<programlisting role="C">
GAllocator *allocator;
GList *list = NULL;
guint i;

/* set a new allocation pool for GList nodes */
allocator = g_allocator_new ("list heap", 1024);
g_list_push_allocator (allocator);

/* do some list operations */
for (i = 0; i < 4096; i++)
  list = g_list_prepend (list, NULL);
list = g_list_reverse (list);

/* beware to pop allocator befor calling external functions */
g_list_pop_allocator ();
gtk_label_set_text (GTK_LABEL (some_label), "some text");

/* and set our private glist pool again */
g_list_push_allocator (allocator);

/* do some list operations */
g_list_free (list);
list = NULL;
for (i = 0; i < 4096; i++)
  list = g_list_prepend (list, NULL);
  
/* and back out (while freeing all of the list nodes in our pool) */
g_list_pop_allocator ();
g_allocator_free (allocator);
</programlisting>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>Why use g_print, g_malloc, g_strdup and fellow glib
functions?</title>

<para>Thanks to Tim Janik who wrote to gtk-list: (slightly
modified)</para>

<para><quote>Regarding g_malloc(), g_free() and siblings, these
functions are much safer than their libc equivalents. For
example, g_free() just returns if called with NULL. Also, if
USE_DMALLOC is defined, the definition for these functions
changes (in glib.h) to use MALLOC(), FREE() etc... If
MEM_PROFILE or MEM_CHECK are defined, there are even small
statistics made counting the used block sizes (shown by
g_mem_profile() / g_mem_check()).</quote></para>

<para><quote>Considering the fact that glib provides an interface for
memory chunks to save space if you have lots of blocks that
are always the same size and to mark them ALLOC_ONLY if
needed, it is just straight forward to create a small saver
(debug able) wrapper around the normal malloc/free stuff as
well - just like gdk covers Xlib. ;)</quote></para>

<para><quote>Using g_error() and g_warning() inside of applications
like the GIMP that fully rely on gtk even gives the
opportunity to pop up a window showing the messages inside of
a gtk window with your own handler (by using
g_set_error_handler()) along the lines of
<literal>gtk_print()</literal> (inside of
gtkmain.c).</quote></para>

</sect1>

<!-- ----------------------------------------------------------------- -->

<sect1>
<title>What's a GScanner and how do I use one?</title>

<para>A GScanner will tokenize your text, that is, it'll return
an integer for every word or number that appears in its input
stream, following certain (customizable) rules to perform this
translation. You still need to write the parsing functions on
your own though.</para>

<para>Here's a little test program supplied by Tim Janik that
will parse</para>

<para><literallayout>
<literal>&lt;SYMBOL&gt; = &lt;OPTIONAL-MINUS&gt; &lt;NUMBER&gt; ;</literal>
</literallayout></para>

<para>constructs, while skipping "#\n" and "/**/" style
comments.</para>

<programlisting role="C">
#include &lt;glib.h&gt;

/* some test text to be fed into the scanner */
static const gchar *test_text =
( "ping = 5;\n"
  "/* slide in some \n"
  " * comments, just for the\n"
  " * fun of it \n"
  " */\n"
  "pong = -6; \n"
  "\n"
  "# the next value is a float\n"
  "zonk = 0.7;\n"
  "# redefine ping\n"
  "ping = - 0.5;\n" );

/* define enumeration values to be returned for specific symbols */
enum {
  SYMBOL_PING = G_TOKEN_LAST + 1,
  SYMBOL_PONG = G_TOKEN_LAST + 2,
  SYMBOL_ZONK = G_TOKEN_LAST + 3
};

/* symbol array */
static const struct {
  gchar *symbol_name;
  guint  symbol_token;
} symbols[] = {
  { "ping", SYMBOL_PING, },
  { "pong", SYMBOL_PONG, },
  { "zonk", SYMBOL_ZONK, },
  { NULL, 0, },
}, *symbol_p = symbols;

static gfloat ping = 0;
static gfloat pong = 0;
static gfloat zonk = 0;

static guint
parse_symbol (GScanner *scanner)
{
  guint symbol;
  gboolean negate = FALSE;

  /* expect a valid symbol */
  g_scanner_get_next_token (scanner);
  symbol = scanner->token;
  if (symbol < SYMBOL_PING ||
      symbol > SYMBOL_ZONK)
    return G_TOKEN_SYMBOL;

  /* expect '=' */
  g_scanner_get_next_token (scanner);
  if (scanner->token != '=')
    return '=';

  /* feature optional '-' */
  g_scanner_peek_next_token (scanner);
  if (scanner->next_token == '-')
    {
      g_scanner_get_next_token (scanner);
      negate = !negate;
    }

  /* expect a float (ints are converted to floats on the fly) */
  g_scanner_get_next_token (scanner);
  if (scanner->token != G_TOKEN_FLOAT)
    return G_TOKEN_FLOAT;

  /* make sure the next token is a ';' */
  if (g_scanner_peek_next_token (scanner) != ';')
    {
      /* not so, eat up the non-semicolon and error out */
      g_scanner_get_next_token (scanner);
      return ';';
    }

  /* assign value, eat the semicolon and exit successfully */
  switch (symbol)
    {
    case SYMBOL_PING:
      ping = negate ? - scanner->value.v_float : scanner->value.v_float;
      break;
    case SYMBOL_PONG:
      pong = negate ? - scanner->value.v_float : scanner->value.v_float;
      break;
    case SYMBOL_ZONK:
      zonk = negate ? - scanner->value.v_float : scanner->value.v_float;
      break;
    }
  g_scanner_get_next_token (scanner);

  return G_TOKEN_NONE;
}

int
main (int argc, char *argv[])
{
  GScanner *scanner;
  guint expected_token;

  scanner = g_scanner_new (NULL);

  /* adjust lexing behaviour to suit our needs
   */
  /* convert non-floats (octal values, hex values...) to G_TOKEN_INT */
  scanner->config->numbers_2_int = TRUE;
  /* convert G_TOKEN_INT to G_TOKEN_FLOAT */
  scanner->config->int_2_float = TRUE;
  /* don't return G_TOKEN_SYMBOL, but the symbol's value */
  scanner->config->symbol_2_token = TRUE;

  /* load symbols into the scanner */
  while (symbol_p->symbol_name)
    {
      g_scanner_add_symbol (scanner,
                            symbol_p->symbol_name,
                            GINT_TO_POINTER (symbol_p->symbol_token));
      symbol_p++;
    }

  /* feed in the text */
  g_scanner_input_text (scanner, test_text, strlen (test_text));

  /* give the error handler an idea on how the input is named */
  scanner->input_name = "test text";

  /* scanning loop, we parse the input until its end is reached,
   * the scanner encountered a lexing error, or our sub routine came
   * across invalid syntax
   */
  do
    {
      expected_token = parse_symbol (scanner);
      
      g_scanner_peek_next_token (scanner);
    }
  while (expected_token == G_TOKEN_NONE &&
         scanner->next_token != G_TOKEN_EOF &&
         scanner->next_token != G_TOKEN_ERROR);

  /* give an error message upon syntax errors */
  if (expected_token != G_TOKEN_NONE)
    g_scanner_unexp_token (scanner, expected_token, NULL, "symbol", NULL, NULL, TRUE);

  /* finsish parsing */
  g_scanner_destroy (scanner);

  /* print results */
  g_print ("ping: %f\n", ping);
  g_print ("pong: %f\n", pong);
  g_print ("zonk: %f\n", zonk);
  
  return 0;
}
</programlisting>

<para>You need to understand that the scanner will parse its
input and tokenize it, it is up to you to interpret these
tokens, not define their types before they get parsed,
e.g. watch gscanner parse a string:</para>

<para><literallayout>
<literal>"hi i am 17"</literal>
<literal> |  | |  |</literal>
<literal> |  | |  v</literal>
<literal> |  | v  TOKEN_INT, value: 17</literal>
<literal> |  v TOKEN_IDENTIFIER, value: "am"</literal>
<literal> v  TOKEN_CHAR, value: 'i'</literal>
<literal>TOKEN_IDENTIFIER, value: "hi"</literal>
</literallayout></para>

<para>If you configure the scanner with:</para>

<programlisting role="C">
scanner->config->int_2_float = TRUE;
scanner->config->char_2_token = TRUE;
scanner->config->scan_symbols = TRUE;
</programlisting>

<para>and add "am" as a symbol with</para>

<programlisting role="C">
g_scanner_add_symbol (scanner, "am", "symbol value");
</programlisting>

<para>GScanner will parse it as</para>

<para><literallayout>
<literal>"hi i am 17"</literal>
<literal> |  | |  |</literal>
<literal> |  | |  v</literal>
<literal> |  | v  TOKEN_FLOAT, value: 17.0  (automatic int->float conversion)</literal>
<literal> |  | TOKEN_SYMBOL, value: "symbol value"  (a successfull hash table lookup</literal>
<literal> |  |                                       turned a TOKEN_IDENTIFIER into a</literal>
<literal> |  |                                       TOKEN_SYMBOL and took over the</literal>
<literal> |  v                                       symbol's value)</literal>
<literal> v  'i'  ('i' can be a valid token as well, as all chars >0 and <256)</literal>
<literal>TOKEN_IDENTIFIER, value: "hi"</literal>
</literallayout></para>

<para>You need to match the token sequence with your code, and
if you encounter something that you don't want, you error
out:</para>

<programlisting role="C">
/* expect an identifier ("hi") */
g_scanner_get_next_token (scanner);
if (scanner->token != G_TOKEN_IDENTIFIER)
  return G_TOKEN_IDENTIFIER;
/* expect a token 'i' */
g_scanner_get_next_token (scanner);
if (scanner->token != 'i')
  return 'i';
/* expect a symbol ("am") */
g_scanner_get_next_token (scanner);
if (scanner->token != G_TOKEN_SYMBOL)
  return G_TOKEN_SYMBOL;
/* expect a float (17.0) */
g_scanner_get_next_token (scanner);
if (scanner->token != G_TOKEN_FLOAT)
  return G_TOKEN_FLOAT;
</programlisting>

<para>If you got past here, you have parsed "hi i am 17" and
would have accepted "dooh i am 42" and  "bah i am 0.75" as
well, but you would have not accepted "hi 7 am 17" or "hi i hi
17".</para>

</sect1>

</chapter>

<!-- ***************************************************************** -->

<chapter>
<title>GTK+ FAQ Contributions, Maintainers and Copyright</title>

<para>If you would like to make a contribution to the FAQ, send either one
of us an e-mail message with the exact text you think should be
included (question and answer). With your help, this document can grow
and become more useful!</para>

<para>This document is maintained by
Tony Gale
<ulink url="mailto:gale@gtk.org">&lt;gale@gtk.org&gt;</ulink>

Nathan Froyd
<ulink url="mailto:maestrox@geocities.com">
&lt;maestrox@geocities.com&gt;</ulink>,
and 
Emmanuel Deloget
<ulink url="mailto:logout@free.fr">&lt;logout@free.fr&gt;</ulink>.

This FAQ was created by Shawn T. Amundson 
<ulink url="mailto:amundson@gimp.org">
&lt;amundson@gimp.org&gt;</ulink> who continues to provide support.

Contributions should be sent to Tony Gale <ulink
url="mailto:gale@gtk.org">&lt;gale@gtk.org&gt;</ulink></para>

<para>The GTK+ FAQ is Copyright (C) 1997-2000 by Shawn T. Amundson, 
Tony Gale, Emmanuel Deloget and Nathan Froyd.</para>

<para>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.</para>

<para>Permission is granted to copy and distribute modified versions of this
document under the conditions for verbatim copying, provided that this
copyright notice is included exactly as in the original, and that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.</para>

<para>Permission is granted to copy and distribute translations of this
document into another language, under the above conditions for
modified versions.</para>

<para>If you are intending to incorporate this document into a published
work, please contact one of the maintainers, and we will make an
effort to ensure that you have the most up to date information
available.</para>

<para>There is no guarentee that this document lives up to its intended
purpose.  This is simply provided as a free resource.  As such, the
authors and maintainers of the information provided within can not
make any guarentee that the information is even accurate.</para>

</chapter>

<!-- ----------------------------------------------------------------- -->

</book>