  GTK+ FAQ
  Tony Gale, Shawn T. Amundson, Emmanuel Deloget, Nathan Froyd
  March 9th 2000

  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+.
  ______________________________________________________________________

  Table of Contents
























































  1. General Information

     1.1 Before anything else: the greetings
     1.2 Authors
     1.3 What is GTK+?
     1.4 What is the + in GTK+?
     1.5 Does the G in GTK+, GDK and GLib stand for?
     1.6 Where is the documentation for GTK+?
     1.7 Is there a mailing list (or mailing list archive) for GTK+?
     1.8 How to get help with GTK+
     1.9 How to report bugs in GTK+
     1.10 Is there a Windows version of GTK+?
     1.11 What applications have been written with GTK+?
     1.12 I'm looking for an application to write in GTK+. How about an IRC client?

  2. How to find, configure, install, and troubleshoot GTK+

     2.1 What do I need to run GTK+?
     2.2 Where can I get GTK+?
     2.3 How do I configure/compile GTK+?
     2.4 When compiling GTK+ I get an error like:
     2.5 I've compiled and installed GTK+, but I can't get any programs to link with it!
     2.6 When compiling programs with GTK+, I get compiler error messages about not being able to find
     2.7 When installing a GTK+ application, configure reports that it can't find GTK.

  3. Development of GTK+

     3.1 Whats this CVS thing that everyone keeps talking about, and how do I access it?
     3.2 How can I contribute to GTK+?
     3.3 How do I know if my patch got applied, and if not, why not?
     3.4 What is the policy on incorporating new widgets into the library?
     3.5 Is anyone working on bindings for languages other than C?

  4. Development with GTK+: the begining

     4.1 How do I get started?
     4.2 I tried to compile a small
     4.3 What about using the
     4.4 I use the backquote stuff in my makefiles, but my make process failed.
     4.5 I want to add some configure stuff, how could I do this?
     4.6 I try to debug my GTK+ application with gdb, but it hangs my X server when I hit some breakpoint. Any Idea ?

  5. Development with GTK+: general questions

     5.1 What widgets are in GTK?
     5.2 Is GTK+ thread safe? How do I write multi-threaded GTK+ applications?
     5.3 Why does this strange 'x io error' occur when I
     5.4 Why don't the contents of a button move when the button is pressed? Here's a patch to make it work that way...
     5.5 How to I identifiy a widgets top level window or other ancestor?
     5.6 How do I get the Window ID of a GtkWindow?
     5.7 How do I catch a double click event (in a list widget, for example)?
     5.8 By the way, what are the differences between signals and events?
     5.9 Data I pass to the
     5.10 I have my signal connected to the the (whatever) event, but it seems I don't catch it. What's wrong?
     5.11 I need to add a new signal to a GTK+ widget. Any idea?
     5.12 Is it possible to get some text displayed which is truncated to fit inside its allocation?
     5.13 How do I make my window modal? / How do I make a single window active?
     5.14 Why doesn't my widget (e.g. progressbar) update?
     5.15 How do I attach data to some GTK+ object/widget?
     5.16 How do I remove the data I have attached to an object?
     5.17 How do I reparent a widget?
     5.18 How could I get any widgets position?
     5.19 How do I set the size of a widget/window? How do I prevent the user resizing my window?
     5.20 How do I add a popup menu to my GTK+ application?
     5.21 How do I disable or enable a widget, such as a button?
     5.22 Shouldn't the text argument in the gtk_clist_* functions be declared const?
     5.23 How do I render pixels (image data) to the screen?
     5.24 How do I create a pixmap without having my window realized/shown?

  6. Development with GTK+: widget specific questions

     6.1 How do I find out about the selection of a GtkList?
     6.2 How do I stop the column headings of a GtkCList disappearing when the list is scrolled?
     6.3 I don't want the user of my applications to enter text into a GtkCombo. Any idea?
     6.4 How do I catch a combo box change?
     6.5 How can I define a separation line in a menu?
     6.6 How can I right justify a menu, such as Help?
     6.7 How do I add some underlined accelerators to menu items?
     6.8 How can I retrieve the text from a GtkMenuItem?
     6.9 How do I right (or otherwise) justify a GtkLabel?
     6.10 How do I set the background color of a GtkLabel widget?
     6.11 How do I set the color and font of a GtkLabel using a Resource File?
     6.12 How do I configure Tooltips in a Resource File?
     6.13 I can't add more than (something like) 2000 chars in a GtkEntry. What's wrong?
     6.14 How do I make a GtkEntry widget activate on pressing the Return key?
     6.15 How do I validate/limit/filter the input to a GtkEntry?
     6.16 How do I use horizontal scrollbars with a GtkText widget?
     6.17 How do I change the font of a GtkText widget?
     6.18 How do I set the cursor position in a GtkText object?

  7. About gdk

     7.1 What is GDK?
     7.2 How do I use color allocation?

  8. About GLib

     8.1 What is GLib?
     8.2 How can I use the doubly linked lists?
     8.3 Memory does not seem to be released when I free the list nodes I've allocated
     8.4 Why use g_print, g_malloc, g_strdup and fellow glib functions?
     8.5 What's a GScanner and how do I use one?

  9. GTK+ FAQ Contributions, Maintainers and Copyright



  ______________________________________________________________________

  1.  General Information

  1.1.  Before anything else: the greetings

  The FAQ authors want to thank:

  o  Havoc Pennington

  o  Erik Mouw

  o  Owen Taylor

  o  Tim Janik

  o  Thomas Mailund Jensen

  o  Joe Pfeiffer

  o  Andy Kahn

  o  Federico Mena Quintero


  o  Damon Chaplin

  o  and all the members of the GTK+ lists

     If we forgot you, please email us !  Thanks again (I know, it's
     really short :)


  1.2.  Authors

  The original authors of GTK+ were:


  o  Peter Mattis

  o  Spencer Kimball

  o  Josh MacDonald

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


  1.3.  What is GTK+?

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

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


  1.4.  What is the + in GTK+?

  Peter Mattis informed the gtk mailing list that:

       "I originally wrote gtk which included the three libraries,
       libglib, libgdk and libgtk. It featured a flat widget hier-
       archy. 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."



  1.5.  Does the G in GTK+, GDK and GLib stand for?

  GTK+ == Gimp Toolkit

  GDK == GTK+ Drawing Kit

  GLib == G Libray





  1.6.  Where is the documentation for GTK+?

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

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

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

  o  Eric Harlows book entitled "Developing Linux Applications with GTK+
     and GDK". The ISBN is 0-7357-0021-4

     The example code from Eric's book is available on-line at
     http://www.bcpl.net/~eharlow/book


  o  Havoc Pennington has released a book called "GTK+/GNOME Application
     Development". The ISBN is 0-7357-0078-8

     The free version of the book lives here:
     http://developer.gnome.org/doc/GGAD/

     And Havoc maintains information about it and errata here:
     http://pobox.com/~hp/gnome-app-devel.html


  1.7.  Is there a mailing list (or mailing list archive) for GTK+?

  Information on mailing lists relating to GTK+ can be found at:

  http://www.gtk.org/mailinglists.html


  1.8.  How to get help with GTK+

  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.


  1.9.  How to report bugs in GTK+

  Bugs should be reported to the GNOME bug tracking system
  (http://bugs.gnome.org). To report a problem about GTK+, send mail to
  submit@bugs.gnome.org.

  The subject of the mail should describe your problem. In the body of
  the mail, you should first include a "pseudo-header" that gives the
  package and version number. This should be separated by a blank line
  from the actual headers.


   Package: gtk+
   Version: 1.2.0



  Substitute 1.2.0 with the version of GTK+ that you have installed.

  Then describe the bug. Include:

  o  Information about your system. For instance:

  o  What operating system and version

  o  What version of X

  o  For Linux, what version of the C library

     And anything else you think is relevant.

  o  How to reproduce the bug.

     If you can reproduce it with the testgtk program that is built in
     the gtk/ subdirectory, that will be most convenient. Otherwise,
     please include a short test program that exhibits the behavior. As
     a last resort, you can also provide a pointer to a larger piece of
     software that can be downloaded.

     (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)

  o  If the bug was a crash, the exact text that was printed out when
     the crash occured.

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


  1.10.  Is there a Windows version of GTK+?

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

  See http://www.iki.fi/tml/gimp/win32 for more information.


  1.11.  What applications have been written with GTK+?

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

  Failing that, look for a project to work on for the GNOME project,
  http://www.gnome.org/ Write a game. Write something that is useful.

  Some of these are:

  o  GIMP (http://www.gimp.org/), an image manipulation program

  o  AbiWord (http://www.abisource.com/), a professional word processor

  o  GUBI (http://www.SoftHome.net/pub/users/timj/gubi/index.htm), a
     user interface builder

  o  Gzilla (http://www.levien.com/gzilla/), a web browser

  o  SANE (http://www.azstarnet.com/~axplinux/sane/ ), a universal
     scanner interface

  o  XQF (http://www.botik.ru/~roma/quake/), a QuakeWorld/Quake2 server
     browser and launcher

  o  ElectricEyes (http://www.labs.redhat.com/ee.shtml), an image viewer
     that aims to be a free replacement for xv

  o  GPK - the General Proxy Kit (http://www.humanfactor.com/gpk/), an
     add-on library to permit thread-safe access to GTK+

  o  GCK - the General Convenience Kit
     (http://www.ii.uib.no/~tomb/gck.html), miscellaneous functions
     intended to ease color handling, UI construction, vector
     operations, and math functions

  o  GDK Imlib (http://www.labs.redhat.com/imlib/), a fast image loading
     and manipulation library for GDK

  o  Glade (http://glade.pn.org/), a GTK+ based RAD tool which produces
     GTK+ applications

  In addition to the above, the GNOME project (http://www.gnome.org) is
  using GTK+ to build a free desktop for Linux. Many more programs can
  be found there.


  1.12.  I'm looking for an application to write in GTK+. How about an
  IRC client?



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


  o  X-Chat.

  o  girc. (Included with GNOME)

  o  gsirc. (In the gnome CVS tree)


  2.  How to find, configure, install, and troubleshoot GTK+

  2.1.  What do I need to run GTK+?

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


  2.2.  Where can I get GTK+?

  The canonical site is:

  ftp://ftp.gtk.org/pub/gtk


  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
  ftp://ftp.gtk.org/etc/mirrors

  Here's a few mirror sites to get you started:

  o  Africa - ftp://ftp.is.co.za/applications/gimp/

  o  Australia - ftp://ftp.au.gimp.org/pub/gimp/

  o  Finland - ftp://ftp.funet.fi/pub/sci/graphics/packages/gimp

  o  Germany - ftp://infosoc.uni-koeln.de/pub/ftp.gimp.org/

  o  Japan - ftp://SunSITE.sut.ac.jp/pub/archives/packages/gimp/

  o  UK - ftp://ftp.flirble.org/pub/X/gimp/

  o  US - ftp://ftp.insync.net/pub/mirrors/ftp.gimp.org/


  2.3.  How do I configure/compile GTK+?

  Generally, all you will need to do is issue the commands:

  ./configure
  make


  in the gtk+-version/ directory.


  2.4.  When compiling GTK+ I get an error like: make: file `Makefile'
  line 456: Syntax error

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



  2.5.  I've compiled and installed GTK+, but I can't get any programs
  to link with it!

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

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

     /usr/X11R6/lib
     /usr/local/lib


  Then you need to run /sbin/ldconfig as root. You can find what direc-
  tory GTK is in using

  gtk-config --libs



  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):

  export LD_LIBRARY_PATH=/usr/local/lib


  and in a csh, you can do:

  setenv LD_LIBRARY_PATH /usr/local/lib


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

     rpm -e gtk gtk-devel


  You may also want to remove the packages that depend on gtk (rpm will
  tell you which ones they are). If you don't have a RedHat Linux sys-
  tem, check to make sure that neither

  /usr/lib



  /usr/local/lib


  libgdk, libglib, or libgck.  If they do exist, remove them (and any
  gtk include files, such as /usr/include/gtk and /usr/include/gdk) and
  reinstall gtk+.


  2.6.  When compiling programs with GTK+, I get compiler error messages
  about not being able to find "glibconfig.h" .

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

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

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

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



       CPPFLAGS="-I/usr/local/include/glib/include" ./configure




  for Bourne-compatible shells like bash, or for csh variants:



       setenv CPPFLAGS "-I/usr/local/include/glib/include"
       ./configure




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


  2.7.  When installing a GTK+ application, configure reports that it
  can't find GTK.

  There are several common reasons for this:

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


  o  gtk-config (or another component of GTK) isn't in your path, or
     there is an old version on your system. Type:

     gtk-config --version


  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.


  o  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.

  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.


  3.  Development of GTK+

  3.1.  Whats this CVS thing that everyone keeps talking about, and how
  do I access it?

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

  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.

  The CVS toolset is available as RPM packages from the usual RedHat
  sites.  The latest version is available at
  http://download.cyclic.com/pub/

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

  o  In a bourne shell descendant (e.g. bash) type:

     CVSROOT=':pserver:anonymous@anoncvs.gnome.org:/cvs/gnome'
     export CVSROOT



  o  Next, the first time the source tree is checked out, a cvs login is
     needed.
     cvs login


  This will ask you for a password. There is no password for
  cvs.gimp.org, so just enter a carriage return.

  o  To get the tree and place it in a subdir of your current working
     directory, issue the command:

     cvs -z3 get gtk+



  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:

  cvs -z3 get glib




  3.2.  How can I contribute to GTK+?

  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 diff -ru
  <oldfile> <newfile>.  Then upload the patchfile to:

  ftp://ftp.gtk.org/incoming


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

  gtk-<username>-<date yymmdd-n>.patch.gz
  gtk-<username>-<date yymmdd-n>.patch.README


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

  Example:

  gtk-gale-982701-0.patch.gz
  gtk-gale-982701-0.patch.README


  Once you upload anything, send the README to ftp-admin@gtk.org


  3.3.  How do I know if my patch got applied, and if not, why not?

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

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


  3.4.  What is the policy on incorporating new widgets into the
  library?

  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.


  3.5.  Is anyone working on bindings for languages other than C?

  The GTK+ home page (http://www.gtk.org/) presents a list of GTK+
  bindings.


  o  There are several C++ wrappers for GTK+.

  o  the gtk-- package, which is a very small wrapper for GTK+.  You can
     find the home page at:
     http://www.cs.tut.fi/~p150650/gtk/gtk--.html.  The FTP site is
     ftp://ftp.gtk.org/pub/gtk/gtk--.


  o  the VDK package, which was built as the base package of a GTK+
     application Borland-like builder. The home page can be found at
     www.guest.net/homepages/mmotta/VDKHome.

  o  The wxWindows/Gtk package, a free C++ library for cross-platform
     GUI development. The home page of this package is
     http://www.freiburg.linux.de/~wxxt/.




  o  There are three known Objective-c bindings currently in
     development:


  o  The GNOME project's package of choice is objgtk. Objgtk is based on
     the Object class and is maintained by Elliot Lee. Apparently,
     objgtk is being accepted as the `standard' Objective-C binding for
     GTK+.

  o  If you are more inclined towards the GNUstep project, you may want
     to check out GTKKit by Helge Hess.  The intention is to setup a
     GTK+ binding using the FoundationKit.  GTKKit includes nicities
     like writing a XML-type template file to construct a GTK+
     interface.

  o  The GToolKit package, which can be found at
     ftp://ftp.gtk.org/pub/gtk/objc-gtoolkit/.




  o  Perl bindings ftp://ftp.gtk.org/pub/gtk/perl


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

  o  David Monniaux reports:

       I've started a gtk-O'Caml binding system.  The basics of the
       system, including callbacks, work fine.

       The current development is in http://www.ens-lyon.fr/~dmon-
       niau/arcs



  o  Several python bindings have been done:


  o  pygtk is at http://www.daa.com.au/~james/pygtk and
     ftp://ftp.gtk.org/pub/gtk/python

  o  python-gtk is at http://www.ucalgary.ca/~nascheme/python-gtk


  o  There's are a couple of OpenGL/Mesa widgets available for GTK+. I
     suggest you start at
     http://www.student.oulu.fi/~jlof/gtkglarea/index.html


  o  Last, there are a lot of other language bindings for languages such
     as Eiffel, TOM, Pascal, Pike, etc.


  4.  Development with GTK+: the begining

  4.1.  How do I get started?

  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 http://www.gtk.org/tutorial/, which is undergoing
  development. This will introduce you to writing applications using C.

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


  4.2.  I tried to compile a small Hello World  of mine, but it failed.
  Any clue?

  Since you are good at coding, we will not deal with compile time error
  here :).

  The classic command line to compile a GTK+ based program is


  gcc -o myprg [c files list] `gtk-config --cflags --libs`



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


  The command line above ensure that:

  o  the correct C compiler flags will be used to compile the program
     (including the complete C header directory list)

  o  your program will be linked with the needed libraries.


  4.3.  What about using the make  utility?

  This is a sample makefile which compile a GTK+ based program:



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

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

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

       # end of file




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


  4.4.  I use the backquote stuff in my makefiles, but my make process
  failed.

  The backquote construction seems to not be accepted by some old make
  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
  ftp://ftp.gnu.org/).


  4.5.  I want to add some configure stuff, how could I do this?

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


  o  the m4 preprocessor v1.4 or better

  o  autoconf v2.13 or better

  o  automake v1.4 or better

  You'll find these packages on the GNU main ftp server
  (ftp://ftp.gnu.org/) or on any GNU mirror.

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


       dnl Process this file with autoconf to produce a configure script.
       dnl configure.in for a GTK+ based program

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

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

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

       AC_OUTPUT(
               Makefile
       )dnl




  You must add a Makefile.am file:



       bin_PROGRAMS    = myprg
       myprg_SOURCES   = myprg.c foo.c bar.c
       INCLUDES        = @GTK_CFLAGS@
       LDADD           = @GTK_LIBS@
       CLEANFILES      = *~
       DISTCLEANFILES  = .deps/*.P




  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:



       SUBDIRS         = mydir1 mydir2 mydir3




  then, to use these, simply type the following commands:


  aclocal
  autoheader
  autoconf
  automake --add-missing --include-deps --foreign



  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).


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


  From Federico Mena Quintero:

       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.

       Run your program with the "--sync" 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.


  Eric Mouw had another solution:

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



  5.  Development with GTK+: general questions

  5.1.  What widgets are in GTK?

  The GTK+ Tutorial lists the following widgets:








































    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




  5.2.  Is GTK+ thread safe? How do I write multi-threaded GTK+ applica-
  tions?

  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.

  When GLib is intialized to be thread-safe, GTK+ is thread aware. 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.

  A minimal main program for a threaded GTK+ application looks like:


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

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

    window = create_window();
    gtk_widget_show(window);

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

    return(0);
  }



  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.

  Erik Mouw contributed the following code example to illustrate how to
  use threads within GTK+ programs.
       /*-------------------------------------------------------------------------
        * Filename:      gtk-thread.c
        * Version:       0.99.1
        * Copyright:     Copyright (C) 1999, Erik Mouw
        * Author:        Erik Mouw <J.A.K.Mouw@its.tudelft.nl>
        * Description:   GTK threads example.
        * Created at:    Sun Oct 17 21:27:09 1999
        * Modified by:   Erik Mouw <J.A.K.Mouw@its.tudelft.nl>
        * Modified at:   Sun Oct 24 17:21:41 1999
        *-----------------------------------------------------------------------*/
       /*
        * Compile with:
        *
        * cc -o gtk-thread gtk-thread.c `gtk-config --cflags --libs gthread`
        *
        * Thanks to Sebastian Wilhelmi and Owen Taylor for pointing out some
        * bugs.
        *
        */

       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <time.h>
       #include <gtk/gtk.h>
       #include <glib.h>
       #include <pthread.h>

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

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

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

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

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

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

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

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

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

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

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

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

    return(NULL);
  }

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

    /* init threads */
    g_thread_init(NULL);

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

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

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

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

    gtk_container_set_border_width(GTK_CONTAINER (window), 10);

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

    /* show everything */
    gtk_widget_show(label);
    gtk_widget_show (window);

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

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

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

    return(0);
  }






  5.3.  Why does this strange 'x io error' occur when I fork()  in my
  GTK+ app?

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

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

  The right function to use here is _exit().

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









































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

  #include <stdio.h>
  #include <stdlib.h>
  #include <signal.h>
  #include <sys/types.h>
  #include <sys/wait.h>
  #include <unistd.h>
  #include <gtk/gtk.h>

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

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

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

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

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

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

    /* re-install the signal handler (some systems need this) */
    signal(SIGCHLD, sigchld_handler);

    /* and unblock it */
    sigemptyset(&set);
    sigaddset(&set, SIGCHLD);
    sigprocmask(SIG_UNBLOCK, &set, &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(&argc, &argv);

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

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

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

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

    /* add a button to do something usefull */
    button = gtk_button_new_with_label("Fork me!");

    gtk_signal_connect(GTK_OBJECT (button), "clicked",
                       GTK_SIGNAL_FUNC(fork_me), NULL);

    gtk_container_add(GTK_CONTAINER(window), button);

    /* show everything */
    gtk_widget_show (button);
    gtk_widget_show (window);


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


    /* main loop */
    gtk_main ();

    exit(0);
  }





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

  From: Peter Mattis


       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.

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




  5.5.  How to I identifiy a widgets top level window or other ancestor?

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

  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
  gtk_widget_get_ancestor() as in:



             GtkWidget       *widget;

             widget = gtk_widget_get_ancestor(w, GTK_TYPE_WINDOW);




  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 entry widget simply use:



             GtkWidget       *hbox;
             hbox = gtk_widget_get_ancestor(w, GTK_TYPE_HBOX);





  5.6.  How do I get the Window ID of a GtkWindow?

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


  #include <gdk/gdkx.h>

  Window xwin = GDK_WINDOW_XWINDOW (GTK_WIDGET (my_window)->window);




  5.7.  How do I catch a double click event (in a list widget, for exam-
  ple)?

  Tim Janik wrote to gtk-list (slightly modified):

  Define a signal handler:













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

    return FALSE;
  }




  And connect the handler to your object:



       {
         /* list, list item init stuff */

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

         /* and/or */

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

         /* something else */
       }




  and, Owen Taylor wrote:

  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.)


  5.8.  By the way, what are the differences between signals and events?

  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
  http://www106.pair.com/rhp/sample_chapters.html).

  Moreover, Havoc posted this to the gtk-list

       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.


  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.

  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.



  5.9.  Data I pass to the delete_event  (or other event) handler gets
  corrupted.

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



       gint delete_event_handler (GtkWidget   *widget,
                                  GdkEventAny *event,
                                  gpointer     data);





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

  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.

  For example,



         gtk_widget_add_events(window, GDK_KEY_RELEASE_MASK);




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

  All the event masks are defined in the gdktypes.h file.


  5.11.  I need to add a new signal to a GTK+ widget. Any idea?

  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.


  If you don't think it is the case or if your patch is not applied
  you'll have to use the gtk_object_class_user_signal_new function.
  gtk_object_class_user_signal_new 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 gtk_signal_emit and can be
  handled in the same way as other signals.

  Tim Janik posted this code snippet:



       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);
       }




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


  5.12.  Is it possible to get some text displayed which is truncated to
  fit inside its allocation?

  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.

  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.



       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);



  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).



  5.13.  How do I make my window modal? / How do I make a single window
  active?

  After you create your window, do gtk_grab_add(my_window). And after
  closing the window do gtk_grab_remove(my_window).


  5.14.  Why doesn't my widget (e.g. progressbar) update?


  You are probably doing all the changes within a function without
  returning control to gtk_main(). 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 gtk_main(). You can force the
  drawing queue to be processed using something like:



       while (gtk_main_iteration(FALSE));




  inside you're function that changes the widget.

  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).


  5.15.  How do I attach data to some GTK+ object/widget?

  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.

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



       void gtk_object_set_data(GtkObject *object, const gchar *key, gpointer data);

       gpointer gtk_object_get_data(GtkObject *object, const gchar *key);




  Since a short example is better than any lengthy speech:








  struct my_struct        p1,p2,*result;
  GtkWidget               *w;

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

  result = gtk_object_get_data(GTK_OBJECT(w),"p1 data");




  The gtk_object_set_user_data() and gtk_object_get_user_data()
  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.


  5.16.  How do I remove the data I have attached to an object?

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


  o  destroy the object

  o  replace the data with a new one (with the same key)

  o  replace the data with NULL (with the same key)


  5.17.  How do I reparent a widget?

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



       void gtk_widget_reparent (GtkWidget *widget,
                                 GtkWidget *new_parent)




  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.

  To avoid this problem, simply use the following code snippet:







       gtk_widget_ref(widget);
       gtk_container_remove(GTK_CONTAINER(old_parent), widget);
       gtk_container_add(GTK_CONTAINER(new_parent), widget);
       gtk_widget_unref(widget);





  5.18.  How could I get any widgets position?

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


  o  If you want the position of a widget relative to its parent, you
     should use widget->allocation.x and widget->allocation.y.

  o  If you want the position of a window relative to the X root window,
     you should use gdk_window_get_geometry() gdk_window_get_position()
     or gdk_window_get_origin().

  o  If you want to get the position of the window (including the WM
     decorations), you should use gdk_window_get_root_origin().

  o  Last but not least, if you want to get a Window Manager frame
     position, you should use gdk_window_get_deskrelative_origin().

  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.


  5.19.  How do I set the size of a widget/window? How do I prevent the
  user resizing my window?

  The gtk_widget_set_uposition() function is used to set the position of
  any widget.

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



       void gtk_widget_set_usize (GtkWidget *widget,
                                  gint width,
                                  gint height);

       void gtk_window_set_policy (GtkWindow *window,
                                   gint allow_shrink,
                                   gint allow_grow,
                                   gint auto_shrink);




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

       allow_shrink = FALSE
       allow_grow   = TRUE
       auto_shrink  = FALSE




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



            gtk_widget_set_usize(your_widget, -1, -1);
            gtk_widget_set_usize(your_widget, new_x_size, new_y_size);




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



            gdk_window_move_resize(window->window,
                                   x_pos, y_pos,
                                   x_size, y_size);





  5.20.  How do I add a popup menu to my GTK+ application?

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



       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;
       }





  5.21.  How do I disable or enable a widget, such as a button?

  To disable (or to enable) a widget, use the gtk_widget_set_sensitive()
  function. The first parameter is you widget pointer. The second
  parameter is a boolean value: when this value is TRUE, the widget is
  enabled.
  5.22.  Shouldn't the text argument in the gtk_clist_* functions be
  declared const?

  For example:

  gint gtk_clist_prepend (GtkCList *clist,
                          gchar    *text[]);



  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).

  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.


  5.23.  How do I render pixels (image data) to the screen?

  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.

  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).

  You do NOT want to use gdk_draw_point(), that will be extremely slow.


  5.24.  How do I create a pixmap without having my window real-
  ized/shown?

  Functions such as gdk_pixmap_create_from_xpm() 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
  gdk_pixmap_colormap_create_from_xpm can be used, as in:
















    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),
                 &pixmap_mask, NULL, pixfile);
    pixw = gtk_pixmap_new (pixmap, pixmap_mask);
    gdk_pixmap_unref (pixmap);
    gdk_pixmap_unref (pixmap_mask);





  6.  Development with GTK+: widget specific questions

  6.1.  How do I find out about the selection of a GtkList?

  Get the selection something like this:


       GList *sel;
       sel = GTK_LIST(list)->selection;




  This is how GList is defined (quoting glist.h):


       typedef struct _GList GList;

       struct _GList
       {
         gpointer data;
         GList *next;
         GList *prev;
       };




  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.

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











  selection_mode          GTK_LIST()->selection contents
  ------------------------------------------------------

  GTK_SELECTION_SINGLE    selection is either NULL
                          or contains a GList* pointer
                          for a single selected item.

  GTK_SELECTION_BROWSE    selection is NULL if the list
                          contains no widgets, otherwise
                          it contains a GList* pointer
                          for one GList structure.

  GTK_SELECTION_MULTIPLE  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.

  GTK_SELECTION_EXTENDED  selection is NULL.



  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:

  Upon Initialization:


       {
               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);
               }
       }




  To get known about the selection:






  {
          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");
  }





  6.2.  when the list is scrolled?  How do I stop the column headings of
  a GtkCList disappearing

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



           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);






  6.3.  I don't want the user of my applications to enter text into a
  GtkCombo. Any idea?

  A GtkCombo has an associated entry which can be accessed using the
  following expression:



             GTK_COMBO(combo_widget)->entry




  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:



             void gtk_entry_set_editable(GtkEntry *entry,
                                         gboolean editable);




  Set the editable parameter to FALSE to disable typing into the entry.


  6.4.  How do I catch a combo box change?

  The entry which is associated to your GtkCombo send a "changed" signal
  when:

  o  some text is typed in

  o  the selection of the combo box is changed

  To catch any combo box change, simply connect your signal handler with



             gtk_signal_connect(GTK_COMBO(cb)->entry,
                                "changed",
                                GTK_SIGNAL_FUNC(my_cb_change_handler),
                                NULL);





  6.5.  How can I define a separation line in a menu?

  See the Tutorial for information on how to create menus.  However, to
  create a separation line in a menu, just insert an empty menu item:



       menuitem = gtk_menu_item_new();
       gtk_menu_append(GTK_MENU(menu), menuitem);
       gtk_widget_show(menuitem);





  6.6.  How can I right justify a menu, such as Help?

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



       menu_path = gtk_menu_factory_find (factory,  "<MyApp>/Help");
       gtk_menu_item_right_justify(menu_path->widget);




  If you do not use the MenuFactory, you should simply use:



       gtk_menu_item_right_justify(my_menu_item);








  6.7.  How do I add some underlined accelerators to menu items?

  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 File menu item with only one child (New). The F in
  File and the N in New are underlined, and the relevant accelerators
  are created.



         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);





  6.8.  How can I retrieve the text from a GtkMenuItem?

  You can usually retrieve the label of a specific GtkMenuItem with:



           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), &text);
               g_print ("menu item text: %s\n", text);
             }
           }





  To get the active menu item from a GtkOptionMenu you can do:


       if (GTK_OPTION_MENU (option_menu)->menu_item)
       {
         GtkWidget *menu_item = GTK_OPTION_MENU (option_menu)->menu_item;
       }




  But, there's a catch. For this specific case, you can not get the
  label widget from menu_item 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:



           if (GTK_BIN (option_menu)->child)
           {
             GtkWidget *child = GTK_BIN (option_menu)->child;

             /* do stuff with child */
           }





  6.9.  How do I right (or otherwise) justify a GtkLabel?

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

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



       void gtk_misc_set_alignment (GtkMisc *misc,
                                    gfloat xalign,
                                    gfloat yalign);




  where the xalign and yalign values are floats in [0.00;1.00].



       GtkWidget       *label;

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

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

       /* horizontal : right align, vertical : bottom */
       gtk_misc_set_alignment(GTK_MISK(label), 1.0f, 1.0f);



  6.10.  How do I set the background color of a GtkLabel widget?

  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.

  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.


  6.11.  How do I set the color and font of a GtkLabel using a Resource
  File?

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


  window (name: humphrey)
    hbox
      label (name: mylabel)



  The widget path your pattern needs to match would be:
  humphrey.GtkHBox.mylabel

  The resource file may look something like:


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



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

    label = gtk_label_new("Some Label Text");
    gtk_widget_set_name(label, "mylabel");
    gtk_widget_show(label);




  6.12.  How do I configure Tooltips in a Resource File?

  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.

  So, you resource file should look something like:


  style "postie"
  {
        bg[NORMAL] = {1.0, 1.0, 0.0}
  }
  widget "gtk-tooltips*" style "postie"



  6.13.  I can't add more than (something like) 2000 chars in a GtkEn-
  try. What's wrong?

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



         /* 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);





  6.14.  How do I make a GtkEntry widget activate on pressing the Return
  key?

  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:



         entry = gtk_entry_new();
         gtk_signal_connect (GTK_OBJECT(entry), "activate",
                             GTK_SIGNAL_FUNC(entry_callback),
                             NULL);





  6.15.  How do I validate/limit/filter the input to a GtkEntry?

  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.

















  #include <ctype.h>
  #include <gtk/gtk.h>

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

    for (i=0; i < length; i++) {
      if (!isalpha(text[i]))
        continue;
      result[count++] = islower(text[i]) ? toupper(text[i]) : text[i];
    }

    if (count > 0) {
      gtk_signal_handler_block_by_func (GTK_OBJECT (editable),
                                        GTK_SIGNAL_FUNC (insert_text_handler),
                                        data);
      gtk_editable_insert_text (editable, result, count, position);
      gtk_signal_handler_unblock_by_func (GTK_OBJECT (editable),
                                          GTK_SIGNAL_FUNC (insert_text_handler),
                                          data);
    }
    gtk_signal_emit_stop_by_name (GTK_OBJECT (editable), "insert_text");

    g_free (result);
  }

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

    gtk_init (&argc, &argv);

    /* create a new window */
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW (window), "GTK Entry");
    gtk_signal_connect(GTK_OBJECT (window), "delete_event",
                       (GtkSignalFunc) gtk_exit, NULL);

    entry = gtk_entry_new();
    gtk_signal_connect(GTK_OBJECT(entry), "insert_text",
                       GTK_SIGNAL_FUNC(insert_text_handler),
                       NULL);
    gtk_container_add(GTK_CONTAINER (window), entry);
    gtk_widget_show(entry);

    gtk_widget_show(window);

    gtk_main();
    return(0);
  }







  6.16.  How do I use horizontal scrollbars with a GtkText widget?

  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.


  6.17.  How do I change the font of a GtkText widget?

  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:



       style "text"
       {
         font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"
       }




  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:



         GdkFont *font;
         font = gdk_font_load("-adobe-helvetica-medium-r-normal--*-140-*-*-*-*-*-*");





  6.18.  How do I set the cursor position in a GtkText object?

  Notice that the response is valid for any object that inherits from
  the GtkEditable class.

  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 gtk_text_set_point() function. If you want to set
  the insertion point at the current cursor position, use the following:



         gtk_text_set_point(GTK_TEXT(text),
         gtk_editable_get_position(GTK_EDITABLE(text)));




  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:





  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 (&argc, &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;
  }




  Now, if you really want to change the cursor position, you should use
  the gtk_editable_set_position() function.


  7.  About gdk

  7.1.  What is GDK?

  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.



  7.2.  How do I use color allocation?

  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:







  {
    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, &width, &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);

    ...
  }





  8.  About GLib

  8.1.  What is GLib?

  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.

  It also provides routines for handling:

  o  Doubly Linked Lists

  o  Singly Linked Lists

  o  Timers

  o  String Handling

  o  A Lexical Scanner

  o  Error Functions


  8.2.  How can I use the doubly linked lists?

  The GList object is defined as:



       typedef struct _GList GList;

       struct _GList
       {
         gpointer data;
         GList *next;
         GList *prev;
       };




  To use the GList objects, simply :



       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)&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, &array[4]);




  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.




  8.3.  Memory does not seem to be released when I free the list nodes
  I've allocated

  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.

  To quote Tim Janik:

       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 GAllo-
       cator. Pushing an allocator into g_list will make all subse-
       quent 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):




       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);





  8.4.  Why use g_print, g_malloc, g_strdup and fellow glib functions?

  Thanks to Tim Janik who wrote to gtk-list: (slightly modified)

       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()).

  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. ;)

  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 gtk_print()
  (inside of gtkmain.c).



  8.5.  What's a GScanner and how do I use one?

  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.

  Here's a little test program supplied by Tim Janik that will parse


  <SYMBOL> = <OPTIONAL-MINUS> <NUMBER> ;



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

































  #include <glib.h>

  /* 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;
  }



  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:


  "hi i am 17"
   |  | |  |
   |  | |  v
   |  | v  TOKEN_INT, value: 17
   |  v TOKEN_IDENTIFIER, value: "am"
   v  TOKEN_CHAR, value: 'i'
  TOKEN_IDENTIFIER, value: "hi"



  If you configure the scanner with:

  scanner->config->int_2_float = TRUE;
  scanner->config->char_2_token = TRUE;
  scanner->config->scan_symbols = TRUE;



  and add "am" as a symbol with

  g_scanner_add_symbol (scanner, "am", "symbol value");



  GScanner will parse it as









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



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


  /* 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;



  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".


  9.  GTK+ FAQ Contributions, Maintainers and Copyright

  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!

  This document is maintained by Tony Gale <gale@gtk.org> Nathan Froyd
  <maestrox@geocities.com>, and Emmanuel Deloget <logout@free.fr>.  This
  FAQ was created by Shawn T. Amundson <amundson@gimp.org> who continues
  to provide support.

  Contributions should be sent to Tony Gale <gale@gtk.org>

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

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

  Permission is granted to copy and distribute modified versions of this
  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.

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

  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.

  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.



















































