path: root/doc/user/gettext.in

<!--

  Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 The SCons Foundation

  Permission is hereby granted, free of charge, to any person obtaining
  a copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
  KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

-->

  <para>
  The &t-link-gettext; toolset supports internationalization and localization
  of SCons-based projects. Builders provided by &t-link-gettext; automatize
  generation and updates of translation files. You can manage translations and
  translation templates similarly to how it's done with autotools.
  </para>

  <section>
  <title>Prerequisites</title>
  <para>
    To follow examples provided in this chapter set up your operating system to
    support two or more languages. In following examples we use locales
    <literal>en_US</literal>, <literal>de_DE</literal>, and
    <literal>pl_PL</literal>.
  </para>

  <para>
    Ensure, that you have <ulink
    url="http://www.gnu.org/software/gettext/manual/gettext.html">GNU gettext
    utilities</ulink> installed on your system.
  </para>

  <para>
    To edit translation files you may wish to install <ulink
    url="http://www.poedit.net/">poedit</ulink> editor.
  </para>
  </section>

  <section>
  <title>Simple project</title>
    <para>
    Let's start with a very simple project, the "Hello world" program 
    for example
    <scons_example name="ex1">
    <file name="hello.c" printme="1">
    /* hello.c */
    #include &lt;stdio.h&gt;
    int main(int argc, char* argv[])
    {
      printf("Hello world\n");
      return 0;
    }
    </file>
    </scons_example>

    Prepare a <filename>SConstruct</filename> to compile the program
    as usual.
    <scons_example name="ex2">
    <file name="SConstruct" printme="1">
    # SConstruct
    env = Environment()
    hello = Program(["hello.c"])
    </file>
    </scons_example>
    </para>

    <para>
    Now we'll convert the project to a multi-lingual one. If you don't
    already have <ulink
    url="http://www.gnu.org/software/gettext/manual/gettext.html">GNU gettext
    utilities</ulink> installed, install them from your preffered
    package repository, or download from <ulink
    url="http://ftp.gnu.org/gnu/gettext/">
    http://ftp.gnu.org/gnu/gettext/</ulink>. For the purpose of this example,
    you should have following three locales installed on your system:
    <literal>en_US</literal>, <literal>de_DE</literal> and
    <literal>pl_PL</literal>. On debian, for example, you may enable certain
    locales through <command>dpkg-reconfigure locales</command>.
    </para>

    <para>
    First prepare the <filename>hello.c</filename> program for
    internationalization. Change the previous code so it reads as follows:
    <scons_example name="ex3">
    <file name="hello.c" printme="1">
    /* hello.c */
    #include &lt;stdio.h&gt;
    #include &lt;libintl.h&gt;
    #include &lt;locale.h&gt;
    int main(int argc, char* argv[])
    {
      bindtextdomain("hello", "locale");
      setlocale(LC_ALL, "");
      textdomain("hello");
      printf(gettext("Hello world\n"));
      return 0;
    }
    </file>
    </scons_example>
    Detailed recipes for such conversion can
    be found at <ulink
    url="http://www.gnu.org/software/gettext/manual/gettext.html#Sources">
    http://www.gnu.org/software/gettext/manual/gettext.html#Sources</ulink>.
    The <function>gettext("...")</function> has two purposes.
    First, it marks messages for the <command>xgettext(1)</command> program, which
    we will use to extract from the sources the messages for localization.
    Second, it calls the <literal>gettext</literal> library internals to
    translate the message at runtime.
    </para>

    <para> 
    Now we shall instruct SCons how to generate and maintain translation files.
    For that, use the &b-link-Translate; builder and &b-link-MOFiles; builder.
    The first one takes source files, extracts internationalized
    messages from them, creates so-called <literal>POT</literal> file
    (translation template), and then creates <literal>PO</literal> translation
    files, one for each requested language. Later, during the development
    lifecycle, the builder keeps all these files up-to date. The
    &b-link-MOFiles; builder compiles the <literal>PO</literal> files to binary
    form. Then install the <literal>MO</literal> files under directory
    called <filename>locale</filename>.
    </para>

    <para>  The completed 
    <filename>SConstruct</filename> is as follows:
    <scons_example name="ex4">
    <file name="SConstruct" printme="1">
    # SConstruct
    env = Environment( tools = ['default', 'gettext'] )
    hello = env.Program(["hello.c"])
    env['XGETTEXTFLAGS'] = [
      '--package-name=%s' % 'hello',
      '--package-version=%s' % '1.0',
    ]
    po = env.Translate(["pl","en", "de"], ["hello.c"], POAUTOINIT = 1)
    mo = env.MOFiles(po)
    InstallAs(["locale/en/LC_MESSAGES/hello.mo"], ["en.mo"])
    InstallAs(["locale/pl/LC_MESSAGES/hello.mo"], ["pl.mo"])
    InstallAs(["locale/de/LC_MESSAGES/hello.mo"], ["de.mo"])
    </file>
    </scons_example>
    </para>
    <para>
    Generate the translation files with <command>scons po-update</command>.
    You should see the output from SCons simillar to this:
    <screen>
    user@host:$ scons po-update
    scons: Reading SConscript files ...
    scons: done reading SConscript files.
    scons: Building targets ...
    Entering '/home/ptomulik/projects/tmp'
    xgettext --package-name=hello --package-version=1.0 -o - hello.c
    Leaving '/home/ptomulik/projects/tmp'
    Writting 'messages.pot' (new file)
    msginit --no-translator -l pl -i messages.pot -o pl.po
    Created pl.po.
    msginit --no-translator -l en -i messages.pot -o en.po
    Created en.po.
    msginit --no-translator -l de -i messages.pot -o de.po
    Created de.po.
    scons: done building targets.
    </screen>
    </para>

    <para>
    If everything is right, you should see following new files.
    <screen>
    user@host:$ ls *.po*
    de.po  en.po  messages.pot  pl.po
    </screen>
    </para>

    <para>
    Open <filename>en.po</filename> in <command>poedit</command> and provide
    the English translation to message <literal>"Hello world\n"</literal>. Do the
    same for <filename>de.po</filename> (deutsch) and
    <filename>pl.po</filename> (polish). Let the translations be, for example:
    <itemizedlist>
      <listitem><para>
        <literal>en: "Welcome to beautiful world!\n"</literal>
      </para></listitem>
      <listitem><para>
        <literal>de: "Hallo Welt!\n"</literal>
      </para></listitem>
      <listitem><para>
        <literal>pl: "Witaj swiecie!\n"</literal>
      </para></listitem>
    </itemizedlist>
    </para>
    <para>
    Now compile the project by executing <command>scons</command>. The
    output should be similar to this:
    <screen>
    user@host:$ scons
    scons: Reading SConscript files ...
    scons: done reading SConscript files.
    scons: Building targets ...
    msgfmt -c -o de.mo de.po
    msgfmt -c -o en.mo en.po
    gcc -o hello.o -c hello.c
    gcc -o hello hello.o
    Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo"
    Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo"
    msgfmt -c -o pl.mo pl.po
    Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
    scons: done building targets.
    </screen>
    SCons automatically compiled the <literal>PO</literal> files to binary format
    <literal>MO</literal>, and the <literal>InstallAs</literal> lines installed
    these files under <filename>locale</filename> folder.
    </para>
    <para>
    Your program should be now ready. You may try it as follows (linux):
    <screen>
    user@host:$ LANG=en_US.UTF-8 ./hello
    Welcome to beautiful world
    </screen>
    <screen>
    user@host:$ LANG=de_DE.UTF-8 ./hello
    Hallo Welt
    </screen>
    <screen>
    user@host:$ LANG=pl_PL.UTF-8 ./hello
    Witaj swiecie
    </screen>
    </para>
    <para>
    To demonstrate the further life of translation files, let's change Polish
    translation (<command>poedit pl.po</command>) to <literal>"Witaj drogi
    swiecie\n"</literal>. Run <command>scons</command> to see how scons
    reacts to this
    <screen>
    user@host:$scons
    scons: Reading SConscript files ...
    scons: done reading SConscript files.
    scons: Building targets ...
    msgfmt -c -o pl.mo pl.po
    Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
    scons: done building targets.
    </screen>
    </para>
    <para>
    Now, open <filename>hello.c</filename> and add another one
    <literal>printf</literal> line with new message.
    <scons_example name="ex5">
    <file name="hello.c" printme="1">
    /* hello.c */
    #include &lt;stdio.h&gt;
    #include &lt;libintl.h&gt;
    #include &lt;locale.h&gt;
    int main(int argc, char* argv[])
    {
      bindtextdomain("hello", "locale");
      setlocale(LC_ALL, "");
      textdomain("hello");
      printf(gettext("Hello world\n"));
      printf(gettext("and good bye\n"));
      return 0;
    }
    </file>
    </scons_example>
    </para>
    <para>
    Compile project with <command>scons</command>. This time, the
    <command>msgmerge(1)</command> program is used by SCons to update
    <literal>PO</literal> file. The output from compilation is like:
    <screen>
    user@host:$scons
    scons: Reading SConscript files ...
    scons: done reading SConscript files.
    scons: Building targets ...
    Entering '/home/ptomulik/projects/tmp'
    xgettext --package-name=hello --package-version=1.0 -o - hello.c
    Leaving '/home/ptomulik/projects/tmp'
    Writting 'messages.pot' (messages in file were outdated)
    msgmerge --update de.po messages.pot
    ... done.
    msgfmt -c -o de.mo de.po
    msgmerge --update en.po messages.pot
    ... done.
    msgfmt -c -o en.mo en.po
    gcc -o hello.o -c hello.c
    gcc -o hello hello.o
    Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo"
    Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo"
    msgmerge --update pl.po messages.pot
    ... done.
    msgfmt -c -o pl.mo pl.po
    Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
    scons: done building targets.
    </screen>
    </para>
    <para>
    The next example demonstrates what happens if we change the source code
    in such way that the internationalized messages do not change. The answer
    is that none of translation files (<literal>POT</literal>,
    <literal>PO</literal>) are touched (i.e. no content changes, no
    creation/modification time changed and so on). Let's append another
    line to the program (after the last printf), so its code becomes:
    <scons_example name="ex6">
    <file name="hello.c" printme="1">
    /* hello.c */
    #include &lt;stdio.h&gt;
    #include &lt;libintl.h&gt;
    #include &lt;locale.h&gt;
    int main(int argc, char* argv[])
    {
      bindtextdomain("hello", "locale");
      setlocale(LC_ALL, "");
      textdomain("hello");
      printf(gettext("Hello world\n"));
      printf(gettext("and good bye\n"));
      printf("----------------\n");
      return a;
    }
    </file>
    </scons_example>
    Compile the project. You'll see on your screen
    <screen>
    user@host:$scons
    scons: Reading SConscript files ...
    scons: done reading SConscript files.
    scons: Building targets ...
    Entering '/home/ptomulik/projects/tmp'
    xgettext --package-name=hello --package-version=1.0 -o - hello.c
    Leaving '/home/ptomulik/projects/tmp'
    Not writting 'messages.pot' (messages in file found to be up-to-date)
    gcc -o hello.o -c hello.c
    gcc -o hello hello.o
    scons: done building targets.
    </screen>
    As you see, the internationalized messages ditn't change, so the
    <literal>POT</literal> and the rest of translation files have not
    even been touched.
    </para>
  </section>