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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>54.2. For the Programmer</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="nls-translator.html" title="54.1. For the Translator" /><link rel="next" href="plhandler.html" title="Chapter 55. Writing a Procedural Language Handler" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">54.2. For the Programmer</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="nls-translator.html" title="54.1. For the Translator">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="nls.html" title="Chapter 54. Native Language Support">Up</a></td><th width="60%" align="center">Chapter 54. Native Language Support</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plhandler.html" title="Chapter 55. Writing a Procedural Language Handler">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="NLS-PROGRAMMER"><div class="titlepage"><div><div><h2 class="title" style="clear: both">54.2. For the Programmer</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="nls-programmer.html#NLS-MECHANICS">54.2.1. Mechanics</a></span></dt><dt><span class="sect2"><a href="nls-programmer.html#NLS-GUIDELINES">54.2.2. Message-Writing Guidelines</a></span></dt></dl></div><div class="sect2" id="NLS-MECHANICS"><div class="titlepage"><div><div><h3 class="title">54.2.1. Mechanics</h3></div></div></div><p>

  3.    This section describes how to implement native language support in a

  4.    program or library that is part of the

  5.    <span class="productname">PostgreSQL</span> distribution.

  6.    Currently, it only applies to C programs.

  7.   </p><div class="procedure" id="id-1.10.7.3.2.3"><p class="title"><strong>Adding NLS Support to a Program</strong></p><ol class="procedure" type="1"><li class="step"><p>

  8.      Insert this code into the start-up sequence of the program:

  9. </p><pre class="programlisting">

  10. #ifdef ENABLE_NLS

  11. #include &lt;locale.h&gt;

  12. #endif

  13. 

  14. ...

  15. 

  16. #ifdef ENABLE_NLS

  17. setlocale(LC_ALL, "");

  18. bindtextdomain("<em class="replaceable"><code>progname</code></em>", LOCALEDIR);

  19. textdomain("<em class="replaceable"><code>progname</code></em>");

  20. #endif

  21. </pre><p>

  22.      (The <em class="replaceable"><code>progname</code></em> can actually be chosen

  23.      freely.)

  24.     </p></li><li class="step"><p>

  25.      Wherever a message that is a candidate for translation is found,

  26.      a call to <code class="function">gettext()</code> needs to be inserted.  E.g.:

  27. </p><pre class="programlisting">

  28. fprintf(stderr, "panic level %d\n", lvl);

  29. </pre><p>

  30.      would be changed to:

  31. </p><pre class="programlisting">

  32. fprintf(stderr, gettext("panic level %d\n"), lvl);

  33. </pre><p>

  34.      (<code class="symbol">gettext</code> is defined as a no-op if NLS support is

  35.      not configured.)

  36.     </p><p>

  37.      This tends to add a lot of clutter.  One common shortcut is to use:

  38. </p><pre class="programlisting">

  39. #define _(x) gettext(x)

  40. </pre><p>

  41.      Another solution is feasible if the program does much of its

  42.      communication through one or a few functions, such as

  43.      <code class="function">ereport()</code> in the backend.  Then you make this

  44.      function call <code class="function">gettext</code> internally on all

  45.      input strings.

  46.     </p></li><li class="step"><p>

  47.      Add a file <code class="filename">nls.mk</code> in the directory with the

  48.      program sources.  This file will be read as a makefile.  The

  49.      following variable assignments need to be made here:

  50. 

  51.      </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="varname">CATALOG_NAME</code></span></dt><dd><p>

  52.          The program name, as provided in the

  53.          <code class="function">textdomain()</code> call.

  54.         </p></dd><dt><span class="term"><code class="varname">AVAIL_LANGUAGES</code></span></dt><dd><p>

  55.          List of provided translations — initially empty.

  56.         </p></dd><dt><span class="term"><code class="varname">GETTEXT_FILES</code></span></dt><dd><p>

  57.          List of files that contain translatable strings, i.e., those

  58.          marked with <code class="function">gettext</code> or an alternative

  59.          solution.  Eventually, this will include nearly all source

  60.          files of the program.  If this list gets too long you can

  61.          make the first <span class="quote">“<span class="quote">file</span>”</span> be a <code class="literal">+</code>

  62.          and the second word be a file that contains one file name per

  63.          line.

  64.         </p></dd><dt><span class="term"><code class="varname">GETTEXT_TRIGGERS</code></span></dt><dd><p>

  65.          The tools that generate message catalogs for the translators

  66.          to work on need to know what function calls contain

  67.          translatable strings.  By default, only

  68.          <code class="function">gettext()</code> calls are known.  If you used

  69.          <code class="function">_</code> or other identifiers you need to list

  70.          them here.  If the translatable string is not the first

  71.          argument, the item needs to be of the form

  72.          <code class="literal">func:2</code> (for the second argument).

  73.          If you have a function that supports pluralized messages,

  74.          the item should look like <code class="literal">func:1,2</code>

  75.          (identifying the singular and plural message arguments).

  76.         </p></dd></dl></div><p>

  77.     </p></li></ol></div><p>

  78.    The build system will automatically take care of building and

  79.    installing the message catalogs.

  80.   </p></div><div class="sect2" id="NLS-GUIDELINES"><div class="titlepage"><div><div><h3 class="title">54.2.2. Message-Writing Guidelines</h3></div></div></div><p>

  81.    Here are some guidelines for writing messages that are easily

  82.    translatable.

  83. 

  84.    </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  85.       Do not construct sentences at run-time, like:

  86. </p><pre class="programlisting">

  87. printf("Files were %s.\n", flag ? "copied" : "removed");

  88. </pre><p>

  89.       The word order within the sentence might be different in other

  90.       languages.  Also, even if you remember to call <code class="function">gettext()</code> on

  91.       each fragment, the fragments might not translate well separately.  It's

  92.       better to duplicate a little code so that each message to be

  93.       translated is a coherent whole.  Only numbers, file names, and

  94.       such-like run-time variables should be inserted at run time into

  95.       a message text.

  96.      </p></li><li class="listitem"><p>

  97.       For similar reasons, this won't work:

  98. </p><pre class="programlisting">

  99. printf("copied %d file%s", n, n!=1 ? "s" : "");

  100. </pre><p>

  101.       because it assumes how the plural is formed.  If you figured you

  102.       could solve it like this:

  103. </p><pre class="programlisting">

  104. if (n==1)

  105.     printf("copied 1 file");

  106. else

  107.     printf("copied %d files", n):

  108. </pre><p>

  109.       then be disappointed.  Some languages have more than two forms,

  110.       with some peculiar rules.  It's often best to design the message

  111.       to avoid the issue altogether, for instance like this:

  112. </p><pre class="programlisting">

  113. printf("number of copied files: %d", n);

  114. </pre><p>

  115.      </p><p>

  116.       If you really want to construct a properly pluralized message,

  117.       there is support for this, but it's a bit awkward.  When generating

  118.       a primary or detail error message in <code class="function">ereport()</code>, you can

  119.       write something like this:

  120. </p><pre class="programlisting">

  121. errmsg_plural("copied %d file",

  122.               "copied %d files",

  123.               n,

  124.               n)

  125. </pre><p>

  126.       The first argument is the format string appropriate for English

  127.       singular form, the second is the format string appropriate for

  128.       English plural form, and the third is the integer control value

  129.       that determines which plural form to use.  Subsequent arguments

  130.       are formatted per the format string as usual.  (Normally, the

  131.       pluralization control value will also be one of the values to be

  132.       formatted, so it has to be written twice.)  In English it only

  133.       matters whether <em class="replaceable"><code>n</code></em> is 1 or not 1, but in other

  134.       languages there can be many different plural forms.  The translator

  135.       sees the two English forms as a group and has the opportunity to

  136.       supply multiple substitute strings, with the appropriate one being

  137.       selected based on the run-time value of <em class="replaceable"><code>n</code></em>.

  138.      </p><p>

  139.       If you need to pluralize a message that isn't going directly to an

  140.       <code class="function">errmsg</code> or <code class="function">errdetail</code> report, you have to use

  141.       the underlying function <code class="function">ngettext</code>.  See the gettext

  142.       documentation.

  143.      </p></li><li class="listitem"><p>

  144.       If you want to communicate something to the translator, such as

  145.       about how a message is intended to line up with other output,

  146.       precede the occurrence of the string with a comment that starts

  147.       with <code class="literal">translator</code>, e.g.:

  148. </p><pre class="programlisting">

  149. /* translator: This message is not what it seems to be. */

  150. </pre><p>

  151.       These comments are copied to the message catalog files so that

  152.       the translators can see them.

  153.      </p></li></ul></div><p>

  154.   </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="nls-translator.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="nls.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plhandler.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">54.1. For the Translator </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 55. Writing a Procedural Language Handler</td></tr></table></div></body></html>
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