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<!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>55.2. 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 Vsnapshot" /><link rel="prev" href="nls-translator.html" title="55.1. For the Translator" /><link rel="next" href="plhandler.html" title="Chapter 56. 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">55.2. For the Programmer</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="nls-translator.html" title="55.1. For the Translator">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="nls.html" title="Chapter 55. Native Language Support">Up</a></td><th width="60%" align="center">Chapter 55. Native Language Support</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plhandler.html" title="Chapter 56. 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">55.2. For the Programmer</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="nls-programmer.html#NLS-MECHANICS">55.2.1. Mechanics</a></span></dt><dt><span class="sect2"><a href="nls-programmer.html#NLS-GUIDELINES">55.2.2. Message-writing Guidelines</a></span></dt></dl></div><div class="sect2" id="NLS-MECHANICS"><div class="titlepage"><div><div><h3 class="title">55.2.1. Mechanics</h3></div></div></div><p>
This section describes how to implement native language support in a
program or library that is part of the
<span class="productname">PostgreSQL</span> distribution.
Currently, it only applies to C programs.
</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>
Insert this code into the start-up sequence of the program:
</p><pre class="programlisting">
#ifdef ENABLE_NLS
#include <locale.h>
#endif
...
#ifdef ENABLE_NLS
setlocale(LC_ALL, "");
bindtextdomain("<em class="replaceable"><code>progname</code></em>", LOCALEDIR);
textdomain("<em class="replaceable"><code>progname</code></em>");
#endif
</pre><p>
(The <em class="replaceable"><code>progname</code></em> can actually be chosen
freely.)
</p></li><li class="step"><p>
Wherever a message that is a candidate for translation is found,
a call to <code class="function">gettext()</code> needs to be inserted. E.g.:
</p><pre class="programlisting">
fprintf(stderr, "panic level %d\n", lvl);
</pre><p>
would be changed to:
</p><pre class="programlisting">
fprintf(stderr, gettext("panic level %d\n"), lvl);
</pre><p>
(<code class="symbol">gettext</code> is defined as a no-op if NLS support is
not configured.)
</p><p>
This tends to add a lot of clutter. One common shortcut is to use:
</p><pre class="programlisting">
#define _(x) gettext(x)
</pre><p>
Another solution is feasible if the program does much of its
communication through one or a few functions, such as
<code class="function">ereport()</code> in the backend. Then you make this
function call <code class="function">gettext</code> internally on all
input strings.
</p></li><li class="step"><p>
Add a file <code class="filename">nls.mk</code> in the directory with the
program sources. This file will be read as a makefile. The
following variable assignments need to be made here:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="varname">CATALOG_NAME</code></span></dt><dd><p>
The program name, as provided in the
<code class="function">textdomain()</code> call.
</p></dd><dt><span class="term"><code class="varname">AVAIL_LANGUAGES</code></span></dt><dd><p>
List of provided translations — initially empty.
</p></dd><dt><span class="term"><code class="varname">GETTEXT_FILES</code></span></dt><dd><p>
List of files that contain translatable strings, i.e., those
marked with <code class="function">gettext</code> or an alternative
solution. Eventually, this will include nearly all source
files of the program. If this list gets too long you can
make the first <span class="quote">“<span class="quote">file</span>”</span> be a <code class="literal">+</code>
and the second word be a file that contains one file name per
line.
</p></dd><dt><span class="term"><code class="varname">GETTEXT_TRIGGERS</code></span></dt><dd><p>
The tools that generate message catalogs for the translators
to work on need to know what function calls contain
translatable strings. By default, only
<code class="function">gettext()</code> calls are known. If you used
<code class="function">_</code> or other identifiers you need to list
them here. If the translatable string is not the first
argument, the item needs to be of the form
<code class="literal">func:2</code> (for the second argument).
If you have a function that supports pluralized messages,
the item should look like <code class="literal">func:1,2</code>
(identifying the singular and plural message arguments).
</p></dd></dl></div><p>
</p></li></ol></div><p>
The build system will automatically take care of building and
installing the message catalogs.
</p></div><div class="sect2" id="NLS-GUIDELINES"><div class="titlepage"><div><div><h3 class="title">55.2.2. Message-writing Guidelines</h3></div></div></div><p>
Here are some guidelines for writing messages that are easily
translatable.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
Do not construct sentences at run-time, like:
</p><pre class="programlisting">
printf("Files were %s.\n", flag ? "copied" : "removed");
</pre><p>
The word order within the sentence might be different in other
languages. Also, even if you remember to call <code class="function">gettext()</code> on
each fragment, the fragments might not translate well separately. It's
better to duplicate a little code so that each message to be
translated is a coherent whole. Only numbers, file names, and
such-like run-time variables should be inserted at run time into
a message text.
</p></li><li class="listitem"><p>
For similar reasons, this won't work:
</p><pre class="programlisting">
printf("copied %d file%s", n, n!=1 ? "s" : "");
</pre><p>
because it assumes how the plural is formed. If you figured you
could solve it like this:
</p><pre class="programlisting">
if (n==1)
printf("copied 1 file");
else
printf("copied %d files", n):
</pre><p>
then be disappointed. Some languages have more than two forms,
with some peculiar rules. It's often best to design the message
to avoid the issue altogether, for instance like this:
</p><pre class="programlisting">
printf("number of copied files: %d", n);
</pre><p>
</p><p>
If you really want to construct a properly pluralized message,
there is support for this, but it's a bit awkward. When generating
a primary or detail error message in <code class="function">ereport()</code>, you can
write something like this:
</p><pre class="programlisting">
errmsg_plural("copied %d file",
"copied %d files",
n,
n)
</pre><p>
The first argument is the format string appropriate for English
singular form, the second is the format string appropriate for
English plural form, and the third is the integer control value
that determines which plural form to use. Subsequent arguments
are formatted per the format string as usual. (Normally, the
pluralization control value will also be one of the values to be
formatted, so it has to be written twice.) In English it only
matters whether <em class="replaceable"><code>n</code></em> is 1 or not 1, but in other
languages there can be many different plural forms. The translator
sees the two English forms as a group and has the opportunity to
supply multiple substitute strings, with the appropriate one being
selected based on the run-time value of <em class="replaceable"><code>n</code></em>.
</p><p>
If you need to pluralize a message that isn't going directly to an
<code class="function">errmsg</code> or <code class="function">errdetail</code> report, you have to use
the underlying function <code class="function">ngettext</code>. See the gettext
documentation.
</p></li><li class="listitem"><p>
If you want to communicate something to the translator, such as
about how a message is intended to line up with other output,
precede the occurrence of the string with a comment that starts
with <code class="literal">translator</code>, e.g.:
</p><pre class="programlisting">
/* translator: This message is not what it seems to be. */
</pre><p>
These comments are copied to the message catalog files so that
the translators can see them.
</p></li></ul></div><p>
</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">55.1. 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 56. Writing A Procedural Language Handler</td></tr></table></div></body></html>
