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(gettext.info)gettext grok

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Being a `gettext' grok
======================

   To fully exploit the functionality of the GNU `gettext' library it
is surely helpful to read the source code.  But for those who don't want
to spend that much time in reading the (sometimes complicated) code here
is a list comments:

   * Changing the language at runtime

     For interactive programs it might be useful to offer a selection
     of the used language at runtime.  To understand how to do this one
     need to know how the used language is determined while executing
     the `gettext' function.  The method which is presented here only
     works correctly with the GNU implementation of the `gettext'
     functions.

     In the function `dcgettext' at every call the current setting of
     the highest priority environment variable is determined and used.
     Highest priority means here the following list with decreasing
     priority:

       1. `LANGUAGE'

       2. `LC_ALL'

       3. `LC_xxx', according to selected locale

       4. `LANG'

     Afterwards the path is constructed using the found value and the
     translation file is loaded if available.

     What is now when the value for, say, `LANGUAGE' changes.  According
     to the process explained above the new value of this variable is
     found as soon as the `dcgettext' function is called.  But this
     also means the (perhaps) different message catalog file is loaded.
     In other words: the used language is changed.

     But there is one little hook.  The code for gcc-2.7.0 and up
     provides some optimization.  This optimization normally prevents
     the calling of the `dcgettext' function as long as no new catalog
     is loaded.  But if `dcgettext' is not called the program also
     cannot find the `LANGUAGE' variable be changed (Note: Optimized
     gettext).  A solution for this is very easy.  Include the
     following code in the language switching function.

            /* Change language.  */
            setenv ("LANGUAGE", "fr", 1);
          
            /* Make change known.  */
            {
              extern int  _nl_msg_cat_cntr;
              ++_nl_msg_cat_cntr;
            }

     The variable `_nl_msg_cat_cntr' is defined in `loadmsgcat.c'.  The
     programmer will find himself in need for a construct like this only
     when developing programs which do run longer and provide the user
     to select the language at runtime.  Non-interactive programs (like
     all these little Unix tools) should never need this.