<title>Make and include-files</title>

      <para>C code often starts with a list of files to include, for

	example stdio.h. Some of these files are system-include

	files, some of them are from the project you're now working

	on:

      </para>

      <programlisting>#include &lt;stdio.h&gt;

#include "foo.h"

int main(....</programlisting>

      <para>To make sure that this file is recompiled the moment

        <filename>foo.h</filename> is changed, you have to add it in

        your <filename>Makefile</filename>:</para>

      <programlisting>foo: foo.c foo.h</programlisting>

      <para>The moment your project is getting bigger and you have

	more and more own include-files to maintain, it will be a

	pain to keep track of all include files and the files which

	are depending on it. If you change an include-file but

	forget to recompile all the files which are depending on

	it, the results will be devastating. <command>gcc</command>

	has an option to analyze your files and to produce a list

	of include-files and their dependencies: <option>-MM</option>.

      </para>

      <para>If you add this to your Makefile:</para>

      <programlisting>depend:

	gcc -E -MM *.c &gt; .depend</programlisting>

      <para>and run <userinput>make depend</userinput>, the file

	<filename>.depend</filename> will appear with a list of

	object-files, C-files and the include-files:</para>

      <programlisting>foo.o: foo.c foo.h</programlisting>

      <para>If you change <filename>foo.h</filename>, next time

	you run <command>make</command> all files depending on

	<filename>foo.h</filename> will be recompiled.</para>

      <para>Don't forget to run <command>make depend</command> each

        time you add an include-file to one of your files.</para>

    </sect2>

    <sect2>