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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:

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

• the m4 preprocessor v1.4 or better
• autoconf v2.13 or better
• 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 terminals are dirt cheap but a bit hard to get (here in The Netherlands, YMMV).