gtk2/docs/faq/gtk-faq.sgml

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

<bookinfo>
  <date>January 14th 2004</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>
    <para><emphasis>Note: </emphasis> This FAQ mainly covers GTK+ 1.2. 
	Where the text covers GTK+ 2.x this will be indicated</para>
  </abstract>
</bookinfo>

<toc></toc>

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

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

<sect1>
<title>Note: This FAQ is undergoing conversion to GTK+ 2.x</title>
<para>This FAQ is undergoing conversion to GTK+ 2.x.
Where the text covers GTK+ 2.x this will be indicated by prefixing the
text with: <emphasis>[GTK+ 2.x]</emphasis>. Where this is not
indicated, the text has not yet been updated from GTK+ 1.2 and may
not be totally correct.
</para>
</sect1>

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

<sect1>
<title>Before anything else: the greetings <emphasis>[GTK 2.x]</emphasis></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 <emphasis>[GTK 2.x]</emphasis></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. The people currently
contributing the most code to GTK+ are (in no particular order):</para>


<itemizedlist spacing=Compact>
<listitem>
<simpara>Owen Taylor</simpara>
</listitem>
<listitem>
<simpara>Matthias Clasen</simpara>
</listitem>
<listitem>
<simpara>Federico Mena Quintero</simpara>
</listitem>
<listitem>
<simpara>Soeren Sandmann</simpara>
</listitem>
<listitem>
<simpara>Padraig O'Briain</simpara>
</listitem>
<listitem>
<simpara>Manish Singh</simpara>
</listitem>
<listitem>
<simpara>Kristian Rietveld</simpara>
</listitem>
<listitem>
<simpara>Tor Lillqvist</simpara>
</listitem>
</itemizedlist>

</sect1>

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

<sect1>
<title>What is GTK+? <emphasis>[GTK 2.x]</emphasis></title>

<para>GTK+ is a multi-platform toolkit for creating graphical user
interfaces, originally designed with
the general look and feel of Motif.  In reality, it looks much
better than Motif.  It contains common and complex widgets, such as
file selection, and color selection widgets.</para>

<para>GTK+ was initially developed as a widget set for the GIMP (GNU Image
Manipulation Program). It has grown extensively since then, and is today
used by a large number of applications, and is the toolkit used by the
<ulink url="http://www.gnome.org/">GNOME</ulink> desktop project.</para>

<para>GTK+ is free software and part of the GNU Project. However, the
licensing terms for GTK+, the GNU LGPL, allow it to be used by all developers,
including those developing proprietary software, without any license fees
or royalties.</para>

<para>GTK+ has been designed from the ground up to support a range of
<ulink url="http://www.gtk.org/bindings.html">
language bindings</ulink>, not only C/C++. Using GTK+ from languages
such as Perl and Python (especially in combination with the Glade GUI
builder) provides an effective method of rapid application
development..</para>
</sect1>

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

<sect1>
<title>What is the + in GTK+? <emphasis>[GTK 2.x]</emphasis></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>

<para>Although much has changed with GTK+, and Peter, Spencer and Josh
don't have any direct involvement these days, the name is kept to keep
a link with the heritage of GTK+.</para>

<para>GTK+ is now additionally based upon the Pango and ATK
libraries, that provide text layout and rendering and accessibility
interfaces.</para>
</sect1>

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

<sect1>
<title>Does the G in GTK+, GDK and GLib stand for? <emphasis>[GTK 2.x]</emphasis></title>

<para>GTK+ == The GIMP Toolkit</para>
<para>GDK == GTK+ Drawing Kit</para>
<para>GLib == G Library</para>

</sect1>

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

<sect1>
<title>Where is the documentation for GTK+? <emphasis>[GTK 2.x]</emphasis></title>

<para>In the GTK+ distribution's doc/ directory you will find
the API Reference 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 few books available that deal with
programming GTK+, GDK and GNOME. Unfortunately, they
currently are all based upon GTK+ 1.x:</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>
<listitem><simpara>"GTK+ Programming in C" by
Syd Logan. ISBN: 0-1301-4264-6</simpara>
</listitem>
<listitem><simpara>"Linux GNOME/GTK+ Programming Bible" by
Arthur Griffith. ISBN: 0-7645-4640-6</simpara>
</listitem>
<listitem><simpara>"Beginning GTK+/GNOME Programming" by
Peter Wright. ISBN: 1-8610-0381-1</simpara>
</listitem>
<listitem><simpara>"Sams Teach Yourself GTK+ Programming
in 21 Days" by Donna Martin
. ISBN: 0-6723-1829-6</simpara>
</listitem>
</itemizedlist>

</sect1>

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

<sect1 id="faq-MailLists">
<title>Is there a mailing list (or mailing list archive) for
GTK+? <emphasis>[GTK 2.x]</emphasis></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+ <emphasis>[GTK 2.x]</emphasis></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+ <emphasis>[GTK 2.x]</emphasis></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 complete, 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. If you can easily reproduce this
crash then running the program under a debugger (e.g. gdb) and getting
a backtrace when the crash occurs is very useful.</simpara>
</listitem>

<listitem><simpara> Further information such as stack traces
may be useful. 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+? <emphasis>[GTK 2.x]</emphasis></title>

<para>The Win32 port of GTK+ is maintained concurrently with the Xwindows
version in CVS. As such it is a supported architecture.</para>

<para>The Win32 port has been predominately done by Tor Lillqvist. Tor
maintains some information on <ulink url="http://www.gimp.org/~tml/gimp/win32/">
GTK+ and GIMP for Windows</ulink>.</para>

<para>There is a pre-compiled, easy-to-install version of GTK+ for
windows on the <ulink url="http://www.dropline.net/gtk/">
Dropline GTK+</ulink> site.</para>

</sect1>

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

<sect1>
<title>What applications have been written with GTK+? <emphasis>[GTK 2.x]</emphasis></title>

<para>The GNOME software map contains a catalogue of software that is
built using GNOME and GTK+. The catalogue is searchable and browsable, so
provides easy access.</para>

<para>Some of the best known projects utilising GTK+ 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.abiword.org/">http://www.abiword.com/</ulink>),
a professional word processor</simpara>
</listitem>
<listitem><simpara> Dia (<ulink
url="http://www.lysator.liu.se/~alla/dia/dia.html">
http://www.lysator.liu.se/~alla/dia/dia.html</ulink>),
a diagram creation program</simpara>
</listitem>
<listitem><simpara> GnuCash (<ulink
url="http://www.gnucash.org/">
http://www.gnucash.org/</ulink>),
a personal finance manager</simpara>
</listitem>
<listitem><simpara> Gnumeric (<ulink
url="http://www.gnome.org/projects/gnumeric/">
http://www.gnome.org/projects/gnumeric/</ulink>),
the GNOME spreadsheet application</simpara>
</listitem>
<listitem><simpara> Glade (<ulink
url="http://glade.gnome.org/">http://glade.gnome.org/</ulink>), a
GTK+ based RAD tool which produces GTK+ and GNOME applications</simpara>
</listitem>
<listitem><simpara> Anjuta (<ulink
url="http://anjuta.sourceforge.net/">http://anjuta.sourceforge.net/</ulink>),
a versatile Integrated Development Environment (IDE) using C and C++ for GTK+
and GIMP.</simpara>
</listitem>
</itemizedlist>
</sect1>

</chapter>

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

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

<sect1 id="faq-Compile">
<title>What do I need to compile GTK+? <emphasis>[GTK 2.x]</emphasis></title>

<para>GTK+ is a large package that is dependent on a number of other
tools and libraries. It is recommended that you use precompiled
binary packages for your system if possible</para>

<para>To compile GTK+ from source you need a C compiler (gcc) and
the X Window System and associated development libraries and packages
on your system.</para>

<para>You will also need to have installed the tools
and libraries that GTK+ depends upon. These are listed below in the order
in which they need to be installed:</para>

<itemizedlist spacing=compact>
<listitem><simpara> pkg-config
(<ulink url="http://www.freedesktop.org/software/pkgconfig">
pkg-config Site</ulink>)</simpara>
</listitem>

<listitem><simpara> GNU make
(<ulink url="http://www.gnu.org/software/make/">
GNU make Site</ulink>)</simpara>
</listitem>

<listitem><simpara> JPEG, PNG and TIFF image libraries
(<ulink url="ftp://ftp.gtk.org/pub/gtk/v2.2/dependencies/">
GTK+ Site</ulink>)</simpara>
</listitem>

<listitem><simpara> FreeType
(<ulink url="http://www.freetype.org/">
FreeType Site</ulink>)</simpara>
</listitem>

<listitem><simpara> fontconfig
(<ulink url="http://www.fontconfig.org/">
fontconfig Site</ulink>)</simpara>
</listitem>

<listitem><simpara> GNU libiconv library (if your system doesn't have iconv())
(<ulink url="http://www.gnu.org/software/libiconv/">
GNU libiconv Site</ulink>)</simpara>
</listitem>

<listitem><simpara> GNU gettext (if your system doesn't have gettext())
(<ulink url="http://www.gnu.org/software/gettext/">
GTK+ Site</ulink>)</simpara>
</listitem>

<listitem><simpara> GLib
(<ulink url="ftp://ftp.gtk.org/pub/gtk/v2.2/">
GTK+ Site</ulink>)</simpara>
</listitem>

<listitem><simpara> Pango
(<ulink url="ftp://ftp.gtk.org/pub/gtk/v2.2/">
GTK+ Site</ulink>)</simpara>
</listitem>

<listitem><simpara> ATK
(<ulink url="ftp://ftp.gtk.org/pub/gtk/v2.2/">
GTK+ Site</ulink>)</simpara>
</listitem>

<listitem><simpara> GTK+
(<ulink url="ftp://ftp.gtk.org/pub/gtk/v2.2/">
GTK+ Site</ulink>)</simpara>
</listitem>
</itemizedlist>

</sect1>

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

<sect1>
<title>Where can I get GTK+? <emphasis>[GTK 2.x]</emphasis></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.planetmirror.com/pub/gimp/gtk">
ftp://ftp.planetmirror.com/pub/gimp/gtk</ulink></simpara> 
</listitem>

<listitem><simpara> Finland -
<ulink url="ftp://ftp.funet.fi/pub/sci/graphics/packages/gimp/gtk">
ftp://ftp.funet.fi/pub/sci/graphics/packages/gimp/gtk</ulink></simpara> 
</listitem>

<listitem><simpara> Germany -
<ulink url="ftp://ftp.gwdg.de/pub/misc/grafik/gimp/gtk">
ftp://ftp.gwdg.de/pub/misc/grafik/gimp/gtk</ulink></simpara> 
</listitem>

<listitem><simpara> Japan -
<ulink url="ftp://sunsite.sut.ac.jp/pub/archives/packages/gimp/gtk">
ftp://sunsite.sut.ac.jp/pub/archives/packages/gimp/gtk</ulink></simpara> 
</listitem>

<listitem><simpara> UK - 
<ulink url="http://www.mirror.ac.uk/sites/ftp.gimp.org/pub/gtk/">
http://www.mirror.ac.uk/sites/ftp.gimp.org/pub/gtk/</ulink></simpara>
</listitem>
</itemizedlist>
</sect1>

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

<sect1>
<title>How do I configure/compile GTK+? <emphasis>[GTK 2.x]</emphasis></title>

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

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

<para>in the GTK+ source directory.</para>

<para>This generally also holds true for each of the packages that GTK+
depends upon, listed <link linkend="faq-Compile">above</link>.</para>

<para>There are various options that you can pass to the configure script
in order to change its default settings. The one that you are most likely
to want to use is the <literal>--prefix</literal>
argument, which defines where the package is to be install, e.g.</para>

<para>
<literallayout><literal>./configure --prefix=/usr</literal></literallayout>
</para>
</sect1>

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

<sect1>
<title>When compiling GTK+ I get an error like: <literal>make:
file `Makefile' line 456: Syntax error</literal> <emphasis>[GTK 2.x]</emphasis></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! <emphasis>[GTK 2.x]</emphasis></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'.</para>

<para>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:</para>

<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 libraries GTK requires using</para>

<para><literallayout><literal>pkg-config gtk+-2.0 --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>

</sect1>

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

<sect1>
<title>When installing a GTK+ application, configure reports
that it can't find GTK. <emphasis>[GTK 2.x]</emphasis></title>

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

<itemizedlist>
<listitem><simpara>You have an old version of GTK installed
somewhere. You should remove this old copy, but note that
this may break applications that have been compiled against
the old version.</simpara>
</listitem>

<listitem><simpara><literal>pkg-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>pkg-config gtk+-2.0 --modversion</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? <emphasis>[GTK 2.x]</emphasis></title>

<para>CVS is the Concurrent Version System and is a very
popular means of version control for software projects. It is
designed to allow multiple authors 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
their 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>

<para>The CVS archive stores both the current development version of
GTK+ (the CVS HEAD branch) and all current and past stable versions.
If you want to retrieve a specific version of GTK+ you have to specify
the CVS tag corresponding to the version you want to checkout. If you
want to checkout the current GTK+ 2.2 stable source code, you would need
to use the following command:</para>

<para><literallayout>
<literal>cvs -z3 get -r gtk-2-2 gtk+</literal>
</literallayout></para>
</sect1>

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

<sect1 id="faq-Patches">
<title>How can I contribute to GTK+? <emphasis>[GTK 2.x]</emphasis></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>.</para>

<para>The patch should then be attached to a bug report in
the GNOME bug tracking system, which can also be used to store
general patches
(<ulink url="http://bugzilla.gnome.org">http://bugzilla.gnome.org</ulink>).
</para>

<para>This method ensures that the patch will not be lost.</para>

</sect1>

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

<sect1>
<title>How do I know if my patch got applied, and if not, why
not? <emphasis>[GTK 2.x]</emphasis></title>

<para>If you have used the GNOME bug tracking system (as stated
<link linkend="faq-Patches">above</link>) then the status
of your patch should be reflected in the bug report.</para>

<para>The GTK+ developers will generally add comments to the bug
report stating what needs to be done to get the patch applied,
or why the patch is not appropriate.</para>
</sect1>

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

<sect1>
<title>What is the policy on incorporating new widgets into
the library? <emphasis>[GTK 2.x]</emphasis></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>

<para>The new widgets that get added to GTK+ are generally either
replacements for existing widgets that are no longer
deemed to be adequate, or have been developed externally to GTK+ but
have been widely tested. One possible avenue for this is via
<ulink url="http://cvs.gnome.org/lxr/source/libegg/">libegg</ulink>.</para>

<para>Before you spend months of your valuable time implementing your
revolutionary widget, it is highly recommended that you get some
feedback on your idea via the appropriate 
<link linkend="faq-MailLists">mailing list</link>.</para>
</sect1>

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

<sect1>
<title>Is anyone working on bindings for languages other than
C? <emphasis>[GTK 2.x]</emphasis></title>

<para>There is a list of <ulink url="http://www.gtk.org/bindings.html">
language bindings</ulink> on the GTK+ website.</para>

<para>The 'official' language bindings are C++, Ada and Python.
However, bindings for many other languages are available.</para>
</sect1>

</chapter>

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

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

<sect1>
<title>How do I get started? <emphasis>[GTK 2.x]</emphasis></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 GTK+ Tutorial doesn't 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 in the
directory 'tests' (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 use the Glade GUI builder with GTK+? <emphasis>[GTK 2.x]</emphasis></title>

<para>There are two ways to use Glade. The first way is to use
Glade's facilities for generating code; the second
way is to use the libglade library which directly loads
the XML user interface description files that Glade
generates into a running program.</para>

<para>Experienced GTK+ programmers generally strongly recommend
using libglade; you don't have to worry about the interaction
between Glade generating the source and you editing it,
and its been shown to be a method that works better
for large projects, so there is a lot of example code
out there you can look at.</para>

<para>An introduction to using libglade can be found in the 
libglade API docs
(<ulink url="http://developer.gnome.org/doc/API/2.0/libglade/libglade-notes.html#libglade-basics">
http://developer.gnome.org/doc/API/2.0/libglade/libglade-notes.html#libglade-basics</ulink>)
.</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?
<emphasis>[GTK 2.x]</emphasis></title>

<para>The short answer to this question is: you can't, so don't write SUID/SGID
programs with GTK+</para>

<para>GTK+ will refuse to run with elevated privileges, as it is not designed
to be used in this manner. The only correct way to write a setuid program with
a graphical user interface is to have a setuid backend that communicates with
the non-setuid graphical user interface via a mechanism such as a pipe and that
considers the input it receives to be untrusted.</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? <emphasis>[GTK 2.x]</emphasis></title>

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

<para>The classic command line to compile a GTK+ based program is</para>
<para><literallayout>
<literal>gcc -o myprog [c files] `pkg-config gtk+-2.0 --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 quotes instead of backquotes. If
you do so, the compiler will complain about an unknown file
called <filename>pkg-config gtk+-2.0 --cflags --libs</filename>. The
text in backquotes is an instruction to your shell to
substitute the output of executing this command into the
commandline.</para>

<para>The command line above ensures 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? <emphasis>[GTK 2.x]</emphasis></title>

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

<programlisting role="C">
# basic GTK+ app makefile
SOURCES = myprg.c foo.c bar.c
OBJS    = ${SOURCES:.c=.o}
CFLAGS  = `pkg-config gtk+-2.0 --cflags`
LDADD   = `pkg-config gtk+-2.0 --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. <emphasis>[GTK 2.x]</emphasis></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/gnu/make/">ftp://ftp.gnu.org/gnu/make/</ulink>).</para>

</sect1>

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

<sect1>
<title>I want to add some configure stuff, how could I do
this? <emphasis>[GTK 2.x]</emphasis></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 v2.54 or better</simpara>
</listitem>

<listitem><simpara>automake v1.7 or better suggested</simpara>
</listitem>
</itemizedlist>

<para>You'll find these packages on the main GNU 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)
AM_INIT_AUTOMAKE(mypkgname, 0.0.1)
AM_CONFIG_HEADER(config.h)

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_2_0(2.2.0,,AC_MSG_ERROR(mypkgname 0.1 needs GTK+ 2.2.0))

AC_OUTPUT(
	Makefile
)
</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? <emphasis>[GTK 2.x]</emphasis></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>

<para>
Another option is to run your application on Xnest. Xnest is an X server
which displays its root window in a regular window of another X server.  
A pointer grab on the Xnest display will not affect the GUI of your debugger
running on your regular X server.
<programlisting>
Xnest :1
twm -display :1
myapp --display=:1
</programlisting>
</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? <emphasis>[GTK 2.x]</emphasis></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>In order to make GDK thread aware, you also need to
call gdk_threads_init() in conjunction with the above call.
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 throughout your code.</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;

  /* init threads */	
  g_thread_init(NULL);
  gdk_threads_init();
  
  /* init gtk */
  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:       1.99.1
 * 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:   Owen Taylor &lt;otaylor@gtk.org&gt;
 * Modified at:   Wed May 28 10:43:00 2003
 *-----------------------------------------------------------------------*/
/*
 * Compile with:
 *
 * cc -o gtk-thread gtk-thread.c `pkg-config --cflags --libs gtk+-2.0 gthread-2.0`
 *
 * Thanks to Sebastian Wilhelmi for pointing out some bugs in earlier versions.
 *
 */

#include &lt;unistd.h&gt;
#include &lt;gtk/gtk.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(g_random_int_range (1, 4));

      /* 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!");

	  /* Make sure all X commands are sent to the X server; not strictly
	   * necessary here, but always a good idea when you do anything
	   * from a thread other than the one where the main loop is running.
	   */
	  gdk_flush ();

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

  return NULL;
}

int main(int argc, char *argv[])
{
  GtkWidget *window;
  GtkWidget *label;
  GError *error = NULL;
  yes_or_no_args yes_args, no_args;

  /* init threads */
  g_thread_init(NULL);
  gdk_threads_init();

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

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

  g_signal_connect(window, "destroy",
		   G_CALLBACK(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;
  if (!g_thread_create(argument_thread, &amp;yes_args, FALSE, &amp;error))
    {
      g_printerr ("Failed to create YES thread: %s\n", error->message);
      return 1;
    }

  no_args.label = label;
  no_args.what = NO_IT_IS_NOT;
  if (!g_thread_create(argument_thread, &amp;no_args, FALSE, &amp;error))
    {
      g_printerr ("Failed to create NO thread: %s\n", error->message);
      return 1;
    }

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

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

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

<sect1>
<title>I'm doing some stuff with GTK+ in a separate thread, and
properly locking with gdk_threads_enter/gdk_threads_leave()
but the display doesn't update properly. <emphasis>[GTK 2.x]</emphasis>
</title>

<para>For efficiency, the X window system batches up commands
and sends them to the X server in batches instead of sending
out immediately.</para>

<para>In a non-multithreaded program, you don't have to worry about
this, since the first thing that happens when control returns
to the main loop is that any outstanding X requests are 
sent to the X server.</para>

<para>However, if you are making GTK+ calls from a thread other
than the main loop, then GTK+ doesn't know when to send batched
commands out. For that reason, after making GTK+ calls 
in a separate thread, it is usually a good idea to call
gdk_flush() before gdk_thread_leave().</para>

<para>Actually, gdk_flush() is more expensive than is necessary here,
since it waits for the X server to finish outstanding commands
as well; if performance is an issue, you may want to call
XFlush() directly:</para>

<programlisting role="C">

#include &lt;gdk/gdkx.h&gt;

void my_flush_commands (void)
{
  GdkDisplay *display = gdk_display_get_default ();
  XFlush (GDK_DISPLAY_XDISPLAY (display);
}
</programlisting>

</sect1>

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

<sect1>
<title>What's an easy way to run a function in the thread with
the main loop? <emphasis>[GTK 2.x]</emphasis></title>

<para>Sometimes the simplest way to set up a threaded program
is to make all the GTK+ calls in a single thread. In such
a program, you should still call g_threads_init(), but
don't need to call gdk_threads_init(), gkd_threads_enter(),
and gdk_threads_leave().</para>

<para>If you set your program up this way, how then do you get
the thread making GTK+ calls and running the main loop
to do something in response to another thread?</para>

<para>An easy way to do it is to take advantage of the fact that
the GLib main loop functions are all thread safe, and can
be called from any thread by adding an idle function
with g_idle_add(). The function provided will be called
at the next opportunity by the main thread. If you want
your function to take priority over event handling and
drawing, you can instead use g_idle_add_full() and pass
in a priority of G_PRIORITY_HIGH.</para>

</sect1>

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

<sect1>
<title>Why does this strange 'x io error' occur when I
<literal>fork()</literal> in my GTK+ app? <emphasis>[GTK 2.x]</emphasis></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:       0.99.2
 * 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
 * Modified by:   Tony Gale &lt;gale@gtk.org&gt;
 * Modified at:   Wed Jan 14 12:38:00 2004
 *-----------------------------------------------------------------------*/
/*
 * Compile with:
 *
 * cc -o gtk-fork gtk-fork.c `pkg-config gtk+-2.0 --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)) &gt; 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);

  g_signal_connect(G_OBJECT (window), "delete_event",
		     G_CALLBACK(delete_event), NULL);
          
  g_signal_connect(G_OBJECT (window), "destroy",
		     G_CALLBACK(destroy), NULL);

#if (GTK_MAJOR_VERSION == 1) &amp;&amp; (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!");
          
  g_signal_connect(G_OBJECT (button), "clicked",
		     G_CALLBACK(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... <emphasis>[GTK 2.x]</emphasis></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? <emphasis>[GTK 2.x]</emphasis></title>

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

<para>You can also follow the a widgets ancestry by using the function
<literal>gtk_widget_get_parent()</literal> that returns a pointer
to a widgets parent widget.</para>

</sect1>

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

<sect1>
<title>How do I get the Window ID of a GtkWindow? <emphasis>[GTK 2.x]</emphasis></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? <emphasis>[GTK 2.x]</emphasis></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_BUTTON(widget) &&
       (event->type==GDK_2BUTTON_PRESS ||
        event->type==GDK_3BUTTON_PRESS) ) {
    printf("I feel %s clicked with 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">
{
  /* button init stuff */     

  g_signal_connect(G_OBJECT(button),
                     "button_press_event",
                     G_CALLBACK(signal_handler_event),
                     NULL);

  /* and/or */

  g_signal_connect(G_OBJECT(button),
                     "button_release_event",
                     G_CALLBACK(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? <emphasis>[GTK 2.x]</emphasis></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_context_iteration(NULL, 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?
<emphasis>[GTK 2.x]</emphasis></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>g_object_set_data()</literal> and
<literal>g_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 g_object_set_data(GObject *object, const gchar *key, gpointer data);

gpointer g_object_get_data(GObject *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;

g_object_set_data(G_OBJECT(w),"p1 data",(gpointer)&amp;p1);
g_object_set_data(G_OBJECT(w),"p2 data",(gpointer)&amp;p2);

result = g_object_get_data(G_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? <emphasis>[GTK 2.x]</emphasis></title>

<para>The <literal>gtk_widget_set_size_request()</literal> function
is used to set the size of a widget to a specific size.

The function
<literal>gtk_window_set_resizable()</literal> function sets whether
the user can resize a window, which they can by default. The
definition of these functions are:</para>

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

void gtk_window_set_resizable (GtkWindow *window,
                               gboolean   resizable);

</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_shell_append(GTK_MENU_SHELL(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? <emphasis>[GTK 2.x]</emphasis></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) {
    g_signal_handlers_block_by_func (G_OBJECT (editable),
                                     G_CALLBACK (insert_text_handler),
                                     data);
    gtk_editable_insert_text (editable, result, count, position);
    g_signal_handlers_unblock_by_func (G_OBJECT (editable),
                                       G_CALLBACK (insert_text_handler),
                                       data);
  }
  g_signal_stop_emission_by_name (G_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");
  g_signal_connect (G_OBJECT (window), "destroy",
                    G_CALLBACK (gtk_main_quit),
                    NULL);

  entry = gtk_entry_new();
  g_signal_connect(G_OBJECT(entry), "insert_text",
		     G_CALLBACK(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>

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

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) 1997-2003 by Shawn T. Amundson, 
Tony Gale.</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>