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<head>
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<title>GNU gettext utilities: 11. The Programmer's View</title>
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<meta name="description" content="GNU gettext utilities: 11. The Programmer's View">
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<table cellpadding="1" cellspacing="1" border="0">
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<tr><td valign="middle" align="left">[<a href="gettext_10.html#SEC173" title="Beginning of this chapter or previous chapter"> << </a>]</td>
|
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<td valign="middle" align="left">[<a href="gettext_12.html#SEC217" title="Next chapter"> >> </a>]</td>
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<td valign="middle" align="left"> </td>
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<td valign="middle" align="left"> </td>
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<td valign="middle" align="left"> </td>
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<td valign="middle" align="left"> </td>
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<td valign="middle" align="left"> </td>
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<td valign="middle" align="left">[<a href="gettext_toc.html#SEC_Top" title="Cover (top) of document">Top</a>]</td>
|
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<td valign="middle" align="left">[<a href="gettext_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
|
||
<td valign="middle" align="left">[<a href="gettext_21.html#SEC389" title="Index">Index</a>]</td>
|
||
<td valign="middle" align="left">[<a href="gettext_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
|
||
</tr></table>
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||
|
||
<hr size="2">
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<a name="Programmers"></a>
|
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<a name="SEC197"></a>
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<h1 class="chapter"> <a href="gettext_toc.html#TOC190">11. The Programmer's View</a> </h1>
|
||
|
||
|
||
<p>One aim of the current message catalog implementation provided by
|
||
GNU <code>gettext</code> was to use the system's message catalog handling, if the
|
||
installer wishes to do so. So we perhaps should first take a look at
|
||
the solutions we know about. The people in the POSIX committee did not
|
||
manage to agree on one of the semi-official standards which we'll
|
||
describe below. In fact they couldn't agree on anything, so they decided
|
||
only to include an example of an interface. The major Unix vendors
|
||
are split in the usage of the two most important specifications: X/Open's
|
||
catgets vs. Uniforum's gettext interface. We'll describe them both and
|
||
later explain our solution of this dilemma.
|
||
</p>
|
||
|
||
|
||
<a name="catgets"></a>
|
||
<a name="SEC198"></a>
|
||
<h2 class="section"> <a href="gettext_toc.html#TOC191">11.1 About <code>catgets</code></a> </h2>
|
||
|
||
<p>The <code>catgets</code> implementation is defined in the X/Open Portability
|
||
Guide, Volume 3, XSI Supplementary Definitions, Chapter 5. But the
|
||
process of creating this standard seemed to be too slow for some of
|
||
the Unix vendors so they created their implementations on preliminary
|
||
versions of the standard. Of course this leads again to problems while
|
||
writing platform independent programs: even the usage of <code>catgets</code>
|
||
does not guarantee a unique interface.
|
||
</p>
|
||
<p>Another, personal comment on this that only a bunch of committee members
|
||
could have made this interface. They never really tried to program
|
||
using this interface. It is a fast, memory-saving implementation, an
|
||
user can happily live with it. But programmers hate it (at least I and
|
||
some others do…)
|
||
</p>
|
||
<p>But we must not forget one point: after all the trouble with transferring
|
||
the rights on Unix they at last came to X/Open, the very same who
|
||
published this specification. This leads me to making the prediction
|
||
that this interface will be in future Unix standards (e.g. Spec1170) and
|
||
therefore part of all Unix implementation (implementations, which are
|
||
<em>allowed</em> to wear this name).
|
||
</p>
|
||
|
||
|
||
<a name="Interface-to-catgets"></a>
|
||
<a name="SEC199"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC192">11.1.1 The Interface</a> </h3>
|
||
|
||
<p>The interface to the <code>catgets</code> implementation consists of three
|
||
functions which correspond to those used in file access: <code>catopen</code>
|
||
to open the catalog for using, <code>catgets</code> for accessing the message
|
||
tables, and <code>catclose</code> for closing after work is done. Prototypes
|
||
for the functions and the needed definitions are in the
|
||
<code><nl_types.h></code> header file.
|
||
</p>
|
||
<a name="IDX1059"></a>
|
||
<p><code>catopen</code> is used like in this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">nl_catd catd = catopen ("catalog_name", 0);
|
||
</pre></td></tr></table>
|
||
|
||
<p>The function takes as the argument the name of the catalog. This usual
|
||
refers to the name of the program or the package. The second parameter
|
||
is not further specified in the standard. I don't even know whether it
|
||
is implemented consistently among various systems. So the common advice
|
||
is to use <code>0</code> as the value. The return value is a handle to the
|
||
message catalog, equivalent to handles to file returned by <code>open</code>.
|
||
</p>
|
||
<a name="IDX1060"></a>
|
||
<p>This handle is of course used in the <code>catgets</code> function which can
|
||
be used like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">char *translation = catgets (catd, set_no, msg_id, "original string");
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||
</pre></td></tr></table>
|
||
|
||
<p>The first parameter is this catalog descriptor. The second parameter
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||
specifies the set of messages in this catalog, in which the message
|
||
described by <code>msg_id</code> is obtained. <code>catgets</code> therefore uses a
|
||
three-stage addressing:
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||
</p>
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||
<table><tr><td> </td><td><pre class="display">catalog name ⇒ set number ⇒ message ID ⇒ translation
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||
</pre></td></tr></table>
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||
|
||
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||
<p>The fourth argument is not used to address the translation. It is given
|
||
as a default value in case when one of the addressing stages fail. One
|
||
important thing to remember is that although the return type of catgets
|
||
is <code>char *</code> the resulting string <em>must not</em> be changed. It
|
||
should better be <code>const char *</code>, but the standard is published in
|
||
1988, one year before ANSI C.
|
||
</p>
|
||
<a name="IDX1061"></a>
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||
<p>The last of these functions is used and behaves as expected:
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||
</p>
|
||
<table><tr><td> </td><td><pre class="example">catclose (catd);
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||
</pre></td></tr></table>
|
||
|
||
<p>After this no <code>catgets</code> call using the descriptor is legal anymore.
|
||
</p>
|
||
|
||
<a name="Problems-with-catgets"></a>
|
||
<a name="SEC200"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC193">11.1.2 Problems with the <code>catgets</code> Interface?!</a> </h3>
|
||
|
||
<p>Now that this description seemed to be really easy — where are the
|
||
problems we speak of? In fact the interface could be used in a
|
||
reasonable way, but constructing the message catalogs is a pain. The
|
||
reason for this lies in the third argument of <code>catgets</code>: the unique
|
||
message ID. This has to be a numeric value for all messages in a single
|
||
set. Perhaps you could imagine the problems keeping such a list while
|
||
changing the source code. Add a new message here, remove one there. Of
|
||
course there have been developed a lot of tools helping to organize this
|
||
chaos but one as the other fails in one aspect or the other. We don't
|
||
want to say that the other approach has no problems but they are far
|
||
more easy to manage.
|
||
</p>
|
||
|
||
<a name="gettext"></a>
|
||
<a name="SEC201"></a>
|
||
<h2 class="section"> <a href="gettext_toc.html#TOC194">11.2 About <code>gettext</code></a> </h2>
|
||
|
||
<p>The definition of the <code>gettext</code> interface comes from a Uniforum
|
||
proposal. It was submitted there by Sun, who had implemented the
|
||
<code>gettext</code> function in SunOS 4, around 1990. Nowadays, the
|
||
<code>gettext</code> interface is specified by the OpenI18N standard.
|
||
</p>
|
||
<p>The main point about this solution is that it does not follow the
|
||
method of normal file handling (open-use-close) and that it does not
|
||
burden the programmer with so many tasks, especially the unique key handling.
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||
Of course here also a unique key is needed, but this key is the message
|
||
itself (how long or short it is). See <a href="#SEC209">Comparing the Two Interfaces</a> for a more
|
||
detailed comparison of the two methods.
|
||
</p>
|
||
<p>The following section contains a rather detailed description of the
|
||
interface. We make it that detailed because this is the interface
|
||
we chose for the GNU <code>gettext</code> Library. Programmers interested
|
||
in using this library will be interested in this description.
|
||
</p>
|
||
|
||
|
||
<a name="Interface-to-gettext"></a>
|
||
<a name="SEC202"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC195">11.2.1 The Interface</a> </h3>
|
||
|
||
<p>The minimal functionality an interface must have is a) to select a
|
||
domain the strings are coming from (a single domain for all programs is
|
||
not reasonable because its construction and maintenance is difficult,
|
||
perhaps impossible) and b) to access a string in a selected domain.
|
||
</p>
|
||
<p>This is principally the description of the <code>gettext</code> interface. It
|
||
has a global domain which unqualified usages reference. Of course this
|
||
domain is selectable by the user.
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">char *textdomain (const char *domain_name);
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||
</pre></td></tr></table>
|
||
|
||
<p>This provides the possibility to change or query the current status of
|
||
the current global domain of the <code>LC_MESSAGE</code> category. The
|
||
argument is a null-terminated string, whose characters must be legal in
|
||
the use in filenames. If the <var>domain_name</var> argument is <code>NULL</code>,
|
||
the function returns the current value. If no value has been set
|
||
before, the name of the default domain is returned: <em>messages</em>.
|
||
Please note that although the return value of <code>textdomain</code> is of
|
||
type <code>char *</code> no changing is allowed. It is also important to know
|
||
that no checks of the availability are made. If the name is not
|
||
available you will see this by the fact that no translations are provided.
|
||
</p>
|
||
<p>To use a domain set by <code>textdomain</code> the function
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">char *gettext (const char *msgid);
|
||
</pre></td></tr></table>
|
||
|
||
<p>is to be used. This is the simplest reasonable form one can imagine.
|
||
The translation of the string <var>msgid</var> is returned if it is available
|
||
in the current domain. If it is not available, the argument itself is
|
||
returned. If the argument is <code>NULL</code> the result is undefined.
|
||
</p>
|
||
<p>One thing which should come into mind is that no explicit dependency to
|
||
the used domain is given. The current value of the domain is used.
|
||
If this changes between two
|
||
executions of the same <code>gettext</code> call in the program, both calls
|
||
reference a different message catalog.
|
||
</p>
|
||
<p>For the easiest case, which is normally used in internationalized
|
||
packages, once at the beginning of execution a call to <code>textdomain</code>
|
||
is issued, setting the domain to a unique name, normally the package
|
||
name. In the following code all strings which have to be translated are
|
||
filtered through the gettext function. That's all, the package speaks
|
||
your language.
|
||
</p>
|
||
|
||
<a name="Ambiguities"></a>
|
||
<a name="SEC203"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC196">11.2.2 Solving Ambiguities</a> </h3>
|
||
|
||
<p>While this single name domain works well for most applications there
|
||
might be the need to get translations from more than one domain. Of
|
||
course one could switch between different domains with calls to
|
||
<code>textdomain</code>, but this is really not convenient nor is it fast. A
|
||
possible situation could be one case subject to discussion during this
|
||
writing: all
|
||
error messages of functions in the set of common used functions should
|
||
go into a separate domain <code>error</code>. By this mean we would only need
|
||
to translate them once.
|
||
Another case are messages from a library, as these <em>have</em> to be
|
||
independent of the current domain set by the application.
|
||
</p>
|
||
<p>For this reasons there are two more functions to retrieve strings:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">char *dgettext (const char *domain_name, const char *msgid);
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||
char *dcgettext (const char *domain_name, const char *msgid,
|
||
int category);
|
||
</pre></td></tr></table>
|
||
|
||
<p>Both take an additional argument at the first place, which corresponds
|
||
to the argument of <code>textdomain</code>. The third argument of
|
||
<code>dcgettext</code> allows to use another locale category but <code>LC_MESSAGES</code>.
|
||
But I really don't know where this can be useful. If the
|
||
<var>domain_name</var> is <code>NULL</code> or <var>category</var> has an value beside
|
||
the known ones, the result is undefined. It should also be noted that
|
||
this function is not part of the second known implementation of this
|
||
function family, the one found in Solaris.
|
||
</p>
|
||
<p>A second ambiguity can arise by the fact, that perhaps more than one
|
||
domain has the same name. This can be solved by specifying where the
|
||
needed message catalog files can be found.
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">char *bindtextdomain (const char *domain_name,
|
||
const char *dir_name);
|
||
</pre></td></tr></table>
|
||
|
||
<p>Calling this function binds the given domain to a file in the specified
|
||
directory (how this file is determined follows below). Especially a
|
||
file in the systems default place is not favored against the specified
|
||
file anymore (as it would be by solely using <code>textdomain</code>). A
|
||
<code>NULL</code> pointer for the <var>dir_name</var> parameter returns the binding
|
||
associated with <var>domain_name</var>. If <var>domain_name</var> itself is
|
||
<code>NULL</code> nothing happens and a <code>NULL</code> pointer is returned. Here
|
||
again as for all the other functions is true that none of the return
|
||
value must be changed!
|
||
</p>
|
||
<p>It is important to remember that relative path names for the
|
||
<var>dir_name</var> parameter can be trouble. Since the path is always
|
||
computed relative to the current directory different results will be
|
||
achieved when the program executes a <code>chdir</code> command. Relative
|
||
paths should always be avoided to avoid dependencies and
|
||
unreliabilities.
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">wchar_t *wbindtextdomain (const char *domain_name,
|
||
const wchar_t *dir_name);
|
||
</pre></td></tr></table>
|
||
|
||
<p>This function is provided only on native Windows platforms. It is like
|
||
<code>bindtextdomain</code>, except that the <var>dir_name</var> parameter is a
|
||
wide string (in UTF-16 encoding, as usual on Windows).
|
||
</p>
|
||
|
||
<a name="Locating-Catalogs"></a>
|
||
<a name="SEC204"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC197">11.2.3 Locating Message Catalog Files</a> </h3>
|
||
|
||
<p>Because many different languages for many different packages have to be
|
||
stored we need some way to add these information to file message catalog
|
||
files. The way usually used in Unix environments is have this encoding
|
||
in the file name. This is also done here. The directory name given in
|
||
<code>bindtextdomain</code>s second argument (or the default directory),
|
||
followed by the name of the locale, the locale category, and the domain name
|
||
are concatenated:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example"><var>dir_name</var>/<var>locale</var>/LC_<var>category</var>/<var>domain_name</var>.mo
|
||
</pre></td></tr></table>
|
||
|
||
<p>The default value for <var>dir_name</var> is system specific. For the GNU
|
||
library, and for packages adhering to its conventions, it's:
|
||
</p><table><tr><td> </td><td><pre class="example">/usr/local/share/locale
|
||
</pre></td></tr></table>
|
||
|
||
<p><var>locale</var> is the name of the locale category which is designated by
|
||
<code>LC_<var>category</var></code>. For <code>gettext</code> and <code>dgettext</code> this
|
||
<code>LC_<var>category</var></code> is always <code>LC_MESSAGES</code>.<a name="DOCF3" href="gettext_fot.html#FOOT3">(3)</a>
|
||
The name of the locale category is determined through
|
||
<code>setlocale (LC_<var>category</var>, NULL)</code>.
|
||
<a name="DOCF4" href="gettext_fot.html#FOOT4">(4)</a>
|
||
When using the function <code>dcgettext</code>, you can specify the locale category
|
||
through the third argument.
|
||
</p>
|
||
|
||
<a name="Charset-conversion"></a>
|
||
<a name="SEC205"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC198">11.2.4 How to specify the output character set <code>gettext</code> uses</a> </h3>
|
||
|
||
<p><code>gettext</code> not only looks up a translation in a message catalog. It
|
||
also converts the translation on the fly to the desired output character
|
||
set. This is useful if the user is working in a different character set
|
||
than the translator who created the message catalog, because it avoids
|
||
distributing variants of message catalogs which differ only in the
|
||
character set.
|
||
</p>
|
||
<p>The output character set is, by default, the value of <code>nl_langinfo
|
||
(CODESET)</code>, which depends on the <code>LC_CTYPE</code> part of the current
|
||
locale. But programs which store strings in a locale independent way
|
||
(e.g. UTF-8) can request that <code>gettext</code> and related functions
|
||
return the translations in that encoding, by use of the
|
||
<code>bind_textdomain_codeset</code> function.
|
||
</p>
|
||
<p>Note that the <var>msgid</var> argument to <code>gettext</code> is not subject to
|
||
character set conversion. Also, when <code>gettext</code> does not find a
|
||
translation for <var>msgid</var>, it returns <var>msgid</var> unchanged –
|
||
independently of the current output character set. It is therefore
|
||
recommended that all <var>msgid</var>s be US-ASCII strings.
|
||
</p>
|
||
<dl>
|
||
<dt><u>Function:</u> char * <b>bind_textdomain_codeset</b><i> (const char *<var>domainname</var>, const char *<var>codeset</var>)</i>
|
||
<a name="IDX1062"></a>
|
||
</dt>
|
||
<dd><p>The <code>bind_textdomain_codeset</code> function can be used to specify the
|
||
output character set for message catalogs for domain <var>domainname</var>.
|
||
The <var>codeset</var> argument must be a valid codeset name which can be used
|
||
for the <code>iconv_open</code> function, or a null pointer.
|
||
</p>
|
||
<p>If the <var>codeset</var> parameter is the null pointer,
|
||
<code>bind_textdomain_codeset</code> returns the currently selected codeset
|
||
for the domain with the name <var>domainname</var>. It returns <code>NULL</code> if
|
||
no codeset has yet been selected.
|
||
</p>
|
||
<p>The <code>bind_textdomain_codeset</code> function can be used several times.
|
||
If used multiple times with the same <var>domainname</var> argument, the
|
||
later call overrides the settings made by the earlier one.
|
||
</p>
|
||
<p>The <code>bind_textdomain_codeset</code> function returns a pointer to a
|
||
string containing the name of the selected codeset. The string is
|
||
allocated internally in the function and must not be changed by the
|
||
user. If the system went out of core during the execution of
|
||
<code>bind_textdomain_codeset</code>, the return value is <code>NULL</code> and the
|
||
global variable <var>errno</var> is set accordingly.
|
||
</p></dd></dl>
|
||
|
||
|
||
<a name="Contexts"></a>
|
||
<a name="SEC206"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC199">11.2.5 Using contexts for solving ambiguities</a> </h3>
|
||
|
||
<p>One place where the <code>gettext</code> functions, if used normally, have big
|
||
problems is within programs with graphical user interfaces (GUIs). The
|
||
problem is that many of the strings which have to be translated are very
|
||
short. They have to appear in pull-down menus which restricts the
|
||
length. But strings which are not containing entire sentences or at
|
||
least large fragments of a sentence may appear in more than one
|
||
situation in the program but might have different translations. This is
|
||
especially true for the one-word strings which are frequently used in
|
||
GUI programs.
|
||
</p>
|
||
<p>As a consequence many people say that the <code>gettext</code> approach is
|
||
wrong and instead <code>catgets</code> should be used which indeed does not
|
||
have this problem. But there is a very simple and powerful method to
|
||
handle this kind of problems with the <code>gettext</code> functions.
|
||
</p>
|
||
<p>Contexts can be added to strings to be translated. A context dependent
|
||
translation lookup is when a translation for a given string is searched,
|
||
that is limited to a given context. The translation for the same string
|
||
in a different context can be different. The different translations of
|
||
the same string in different contexts can be stored in the in the same
|
||
MO file, and can be edited by the translator in the same PO file.
|
||
</p>
|
||
<p>The ‘<tt>gettext.h</tt>’ include file contains the lookup macros for strings
|
||
with contexts. They are implemented as thin macros and inline functions
|
||
over the functions from <code><libintl.h></code>.
|
||
</p>
|
||
<a name="IDX1063"></a>
|
||
<table><tr><td> </td><td><pre class="example">const char *pgettext (const char *msgctxt, const char *msgid);
|
||
</pre></td></tr></table>
|
||
|
||
<p>In a call of this macro, <var>msgctxt</var> and <var>msgid</var> must be string
|
||
literals. The macro returns the translation of <var>msgid</var>, restricted
|
||
to the context given by <var>msgctxt</var>.
|
||
</p>
|
||
<p>The <var>msgctxt</var> string is visible in the PO file to the translator.
|
||
You should try to make it somehow canonical and never changing. Because
|
||
every time you change an <var>msgctxt</var>, the translator will have to review
|
||
the translation of <var>msgid</var>.
|
||
</p>
|
||
<p>Finding a canonical <var>msgctxt</var> string that doesn't change over time can
|
||
be hard. But you shouldn't use the file name or class name containing the
|
||
<code>pgettext</code> call – because it is a common development task to rename
|
||
a file or a class, and it shouldn't cause translator work. Also you shouldn't
|
||
use a comment in the form of a complete English sentence as <var>msgctxt</var> –
|
||
because orthography or grammar changes are often applied to such sentences,
|
||
and again, it shouldn't force the translator to do a review.
|
||
</p>
|
||
<p>The ‘<samp>p</samp>’ in ‘<samp>pgettext</samp>’ stands for “particular”: <code>pgettext</code>
|
||
fetches a particular translation of the <var>msgid</var>.
|
||
</p>
|
||
<a name="IDX1064"></a>
|
||
<a name="IDX1065"></a>
|
||
<table><tr><td> </td><td><pre class="example">const char *dpgettext (const char *domain_name,
|
||
const char *msgctxt, const char *msgid);
|
||
const char *dcpgettext (const char *domain_name,
|
||
const char *msgctxt, const char *msgid,
|
||
int category);
|
||
</pre></td></tr></table>
|
||
|
||
<p>These are generalizations of <code>pgettext</code>. They behave similarly to
|
||
<code>dgettext</code> and <code>dcgettext</code>, respectively. The <var>domain_name</var>
|
||
argument defines the translation domain. The <var>category</var> argument
|
||
allows to use another locale category than <code>LC_MESSAGES</code>.
|
||
</p>
|
||
<p>As as example consider the following fictional situation. A GUI program
|
||
has a menu bar with the following entries:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">+------------+------------+--------------------------------------+
|
||
| File | Printer | |
|
||
+------------+------------+--------------------------------------+
|
||
| Open | | Select |
|
||
| New | | Open |
|
||
+----------+ | Connect |
|
||
+----------+
|
||
</pre></td></tr></table>
|
||
|
||
<p>To have the strings <code>File</code>, <code>Printer</code>, <code>Open</code>,
|
||
<code>New</code>, <code>Select</code>, and <code>Connect</code> translated there has to be
|
||
at some point in the code a call to a function of the <code>gettext</code>
|
||
family. But in two places the string passed into the function would be
|
||
<code>Open</code>. The translations might not be the same and therefore we
|
||
are in the dilemma described above.
|
||
</p>
|
||
<p>What distinguishes the two places is the menu path from the menu root to
|
||
the particular menu entries:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Menu|File
|
||
Menu|Printer
|
||
Menu|File|Open
|
||
Menu|File|New
|
||
Menu|Printer|Select
|
||
Menu|Printer|Open
|
||
Menu|Printer|Connect
|
||
</pre></td></tr></table>
|
||
|
||
<p>The context is thus the menu path without its last part. So, the calls
|
||
look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">pgettext ("Menu|", "File")
|
||
pgettext ("Menu|", "Printer")
|
||
pgettext ("Menu|File|", "Open")
|
||
pgettext ("Menu|File|", "New")
|
||
pgettext ("Menu|Printer|", "Select")
|
||
pgettext ("Menu|Printer|", "Open")
|
||
pgettext ("Menu|Printer|", "Connect")
|
||
</pre></td></tr></table>
|
||
|
||
<p>Whether or not to use the ‘<samp>|</samp>’ character at the end of the context is a
|
||
matter of style.
|
||
</p>
|
||
<p>For more complex cases, where the <var>msgctxt</var> or <var>msgid</var> are not
|
||
string literals, more general macros are available:
|
||
</p>
|
||
<a name="IDX1066"></a>
|
||
<a name="IDX1067"></a>
|
||
<a name="IDX1068"></a>
|
||
<table><tr><td> </td><td><pre class="example">const char *pgettext_expr (const char *msgctxt, const char *msgid);
|
||
const char *dpgettext_expr (const char *domain_name,
|
||
const char *msgctxt, const char *msgid);
|
||
const char *dcpgettext_expr (const char *domain_name,
|
||
const char *msgctxt, const char *msgid,
|
||
int category);
|
||
</pre></td></tr></table>
|
||
|
||
<p>Here <var>msgctxt</var> and <var>msgid</var> can be arbitrary string-valued expressions.
|
||
These macros are more general. But in the case that both argument expressions
|
||
are string literals, the macros without the ‘<samp>_expr</samp>’ suffix are more
|
||
efficient.
|
||
</p>
|
||
|
||
<a name="Plural-forms"></a>
|
||
<a name="SEC207"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC200">11.2.6 Additional functions for plural forms</a> </h3>
|
||
|
||
<p>The functions of the <code>gettext</code> family described so far (and all the
|
||
<code>catgets</code> functions as well) have one problem in the real world
|
||
which have been neglected completely in all existing approaches. What
|
||
is meant here is the handling of plural forms.
|
||
</p>
|
||
<p>Looking through Unix source code before the time anybody thought about
|
||
internationalization (and, sadly, even afterwards) one can often find
|
||
code similar to the following:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample"> printf ("%d file%s deleted", n, n == 1 ? "" : "s");
|
||
</pre></td></tr></table>
|
||
|
||
<p>After the first complaints from people internationalizing the code people
|
||
either completely avoided formulations like this or used strings like
|
||
<code>"file(s)"</code>. Both look unnatural and should be avoided. First
|
||
tries to solve the problem correctly looked like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample"> if (n == 1)
|
||
printf ("%d file deleted", n);
|
||
else
|
||
printf ("%d files deleted", n);
|
||
</pre></td></tr></table>
|
||
|
||
<p>But this does not solve the problem. It helps languages where the
|
||
plural form of a noun is not simply constructed by adding an
|
||
‘s’
|
||
but that is all. Once again people fell into the trap of believing the
|
||
rules their language is using are universal. But the handling of plural
|
||
forms differs widely between the language families. For example,
|
||
Rafal Maszkowski <code><rzm@mat.uni.torun.pl></code> reports:
|
||
</p>
|
||
<blockquote><p>In Polish we use e.g. plik (file) this way:
|
||
</p><table><tr><td> </td><td><pre class="example">1 plik
|
||
2,3,4 pliki
|
||
5-21 pliko'w
|
||
22-24 pliki
|
||
25-31 pliko'w
|
||
</pre></td></tr></table>
|
||
<p>and so on (o' means 8859-2 oacute which should be rather okreska,
|
||
similar to aogonek).
|
||
</p></blockquote>
|
||
|
||
<p>There are two things which can differ between languages (and even inside
|
||
language families);
|
||
</p>
|
||
<ul>
|
||
<li>
|
||
The form how plural forms are built differs. This is a problem with
|
||
languages which have many irregularities. German, for instance, is a
|
||
drastic case. Though English and German are part of the same language
|
||
family (Germanic), the almost regular forming of plural noun forms
|
||
(appending an
|
||
‘s’)
|
||
is hardly found in German.
|
||
|
||
</li><li>
|
||
The number of plural forms differ. This is somewhat surprising for
|
||
those who only have experiences with Romanic and Germanic languages
|
||
since here the number is the same (there are two).
|
||
|
||
<p>But other language families have only one form or many forms. More
|
||
information on this in an extra section.
|
||
</p></li></ul>
|
||
|
||
<p>The consequence of this is that application writers should not try to
|
||
solve the problem in their code. This would be localization since it is
|
||
only usable for certain, hardcoded language environments. Instead the
|
||
extended <code>gettext</code> interface should be used.
|
||
</p>
|
||
<p>These extra functions are taking instead of the one key string two
|
||
strings and a numerical argument. The idea behind this is that using
|
||
the numerical argument and the first string as a key, the implementation
|
||
can select using rules specified by the translator the right plural
|
||
form. The two string arguments then will be used to provide a return
|
||
value in case no message catalog is found (similar to the normal
|
||
<code>gettext</code> behavior). In this case the rules for Germanic language
|
||
is used and it is assumed that the first string argument is the singular
|
||
form, the second the plural form.
|
||
</p>
|
||
<p>This has the consequence that programs without language catalogs can
|
||
display the correct strings only if the program itself is written using
|
||
a Germanic language. This is a limitation but since the GNU C library
|
||
(as well as the GNU <code>gettext</code> package) are written as part of the
|
||
GNU package and the coding standards for the GNU project require program
|
||
being written in English, this solution nevertheless fulfills its
|
||
purpose.
|
||
</p>
|
||
<dl>
|
||
<dt><u>Function:</u> char * <b>ngettext</b><i> (const char *<var>msgid1</var>, const char *<var>msgid2</var>, unsigned long int <var>n</var>)</i>
|
||
<a name="IDX1069"></a>
|
||
</dt>
|
||
<dd><p>The <code>ngettext</code> function is similar to the <code>gettext</code> function
|
||
as it finds the message catalogs in the same way. But it takes two
|
||
extra arguments. The <var>msgid1</var> parameter must contain the singular
|
||
form of the string to be converted. It is also used as the key for the
|
||
search in the catalog. The <var>msgid2</var> parameter is the plural form.
|
||
The parameter <var>n</var> is used to determine the plural form. If no
|
||
message catalog is found <var>msgid1</var> is returned if <code>n == 1</code>,
|
||
otherwise <code>msgid2</code>.
|
||
</p>
|
||
<p>An example for the use of this function is:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">printf (ngettext ("%d file removed", "%d files removed", n), n);
|
||
</pre></td></tr></table>
|
||
|
||
<p>Please note that the numeric value <var>n</var> has to be passed to the
|
||
<code>printf</code> function as well. It is not sufficient to pass it only to
|
||
<code>ngettext</code>.
|
||
</p>
|
||
<p>In the English singular case, the number – always 1 – can be replaced with
|
||
"one":
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">printf (ngettext ("One file removed", "%d files removed", n), n);
|
||
</pre></td></tr></table>
|
||
|
||
<p>This works because the ‘<samp>printf</samp>’ function discards excess arguments that
|
||
are not consumed by the format string.
|
||
</p>
|
||
<p>If this function is meant to yield a format string that takes two or more
|
||
arguments, you can not use it like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">printf (ngettext ("%d file removed from directory %s",
|
||
"%d files removed from directory %s",
|
||
n),
|
||
n, dir);
|
||
</pre></td></tr></table>
|
||
|
||
<p>because in many languages the translators want to replace the ‘<samp>%d</samp>’
|
||
with an explicit word in the singular case, just like “one” in English,
|
||
and C format strings cannot consume the second argument but skip the first
|
||
argument. Instead, you have to reorder the arguments so that ‘<samp>n</samp>’
|
||
comes last:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">printf (ngettext ("%2$d file removed from directory %1$s",
|
||
"%2$d files removed from directory %1$s",
|
||
n),
|
||
dir, n);
|
||
</pre></td></tr></table>
|
||
|
||
<p>See <a href="gettext_15.html#SEC267">C Format Strings</a> for details about this argument reordering syntax.
|
||
</p>
|
||
<p>When you know that the value of <code>n</code> is within a given range, you can
|
||
specify it as a comment directed to the <code>xgettext</code> tool. This
|
||
information may help translators to use more adequate translations. Like
|
||
this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">if (days > 7 && days < 14)
|
||
/* xgettext: range: 1..6 */
|
||
printf (ngettext ("one week and one day", "one week and %d days",
|
||
days - 7),
|
||
days - 7);
|
||
</pre></td></tr></table>
|
||
|
||
<p>It is also possible to use this function when the strings don't contain a
|
||
cardinal number:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">puts (ngettext ("Delete the selected file?",
|
||
"Delete the selected files?",
|
||
n));
|
||
</pre></td></tr></table>
|
||
|
||
<p>In this case the number <var>n</var> is only used to choose the plural form.
|
||
</p></dd></dl>
|
||
|
||
<dl>
|
||
<dt><u>Function:</u> char * <b>dngettext</b><i> (const char *<var>domain</var>, const char *<var>msgid1</var>, const char *<var>msgid2</var>, unsigned long int <var>n</var>)</i>
|
||
<a name="IDX1070"></a>
|
||
</dt>
|
||
<dd><p>The <code>dngettext</code> is similar to the <code>dgettext</code> function in the
|
||
way the message catalog is selected. The difference is that it takes
|
||
two extra parameter to provide the correct plural form. These two
|
||
parameters are handled in the same way <code>ngettext</code> handles them.
|
||
</p></dd></dl>
|
||
|
||
<dl>
|
||
<dt><u>Function:</u> char * <b>dcngettext</b><i> (const char *<var>domain</var>, const char *<var>msgid1</var>, const char *<var>msgid2</var>, unsigned long int <var>n</var>, int <var>category</var>)</i>
|
||
<a name="IDX1071"></a>
|
||
</dt>
|
||
<dd><p>The <code>dcngettext</code> is similar to the <code>dcgettext</code> function in the
|
||
way the message catalog is selected. The difference is that it takes
|
||
two extra parameter to provide the correct plural form. These two
|
||
parameters are handled in the same way <code>ngettext</code> handles them.
|
||
</p></dd></dl>
|
||
|
||
<p>Now, how do these functions solve the problem of the plural forms?
|
||
Without the input of linguists (which was not available) it was not
|
||
possible to determine whether there are only a few different forms in
|
||
which plural forms are formed or whether the number can increase with
|
||
every new supported language.
|
||
</p>
|
||
<p>Therefore the solution implemented is to allow the translator to specify
|
||
the rules of how to select the plural form. Since the formula varies
|
||
with every language this is the only viable solution except for
|
||
hardcoding the information in the code (which still would require the
|
||
possibility of extensions to not prevent the use of new languages).
|
||
</p>
|
||
<a name="IDX1072"></a>
|
||
<a name="IDX1073"></a>
|
||
<a name="IDX1074"></a>
|
||
<p>The information about the plural form selection has to be stored in the
|
||
header entry of the PO file (the one with the empty <code>msgid</code> string).
|
||
The plural form information looks like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=2; plural=n == 1 ? 0 : 1;
|
||
</pre></td></tr></table>
|
||
|
||
<p>The <code>nplurals</code> value must be a decimal number which specifies how
|
||
many different plural forms exist for this language. The string
|
||
following <code>plural</code> is an expression which is using the C language
|
||
syntax. Exceptions are that no negative numbers are allowed, numbers
|
||
must be decimal, and the only variable allowed is <code>n</code>. Spaces are
|
||
allowed in the expression, but backslash-newlines are not; in the
|
||
examples below the backslash-newlines are present for formatting purposes
|
||
only. This expression will be evaluated whenever one of the functions
|
||
<code>ngettext</code>, <code>dngettext</code>, or <code>dcngettext</code> is called. The
|
||
numeric value passed to these functions is then substituted for all uses
|
||
of the variable <code>n</code> in the expression. The resulting value then
|
||
must be greater or equal to zero and smaller than the value given as the
|
||
value of <code>nplurals</code>.
|
||
</p>
|
||
<a name="IDX1075"></a>
|
||
<p>The following rules are known at this point. The language with families
|
||
are listed. But this does not necessarily mean the information can be
|
||
generalized for the whole family (as can be easily seen in the table
|
||
below).<a name="DOCF5" href="gettext_fot.html#FOOT5">(5)</a>
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Only one form:</dt>
|
||
<dd><p>Some languages only require one single form. There is no distinction
|
||
between the singular and plural form. An appropriate header entry
|
||
would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=1; plural=0;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Asian family</dt>
|
||
<dd><p>Japanese, Vietnamese, Korean </p></dd>
|
||
<dt> Tai-Kadai family</dt>
|
||
<dd><p>Thai </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Two forms, singular used for one only</dt>
|
||
<dd><p>This is the form used in most existing programs since it is what English
|
||
is using. A header entry would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=2; plural=n != 1;
|
||
</pre></td></tr></table>
|
||
|
||
<p>(Note: this uses the feature of C expressions that boolean expressions
|
||
have to value zero or one.)
|
||
</p>
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Germanic family</dt>
|
||
<dd><p>English, German, Dutch, Swedish, Danish, Norwegian, Faroese </p></dd>
|
||
<dt> Romanic family</dt>
|
||
<dd><p>Spanish, Portuguese, Italian </p></dd>
|
||
<dt> Latin/Greek family</dt>
|
||
<dd><p>Greek </p></dd>
|
||
<dt> Slavic family</dt>
|
||
<dd><p>Bulgarian </p></dd>
|
||
<dt> Finno-Ugric family</dt>
|
||
<dd><p>Finnish, Estonian </p></dd>
|
||
<dt> Semitic family</dt>
|
||
<dd><p>Hebrew </p></dd>
|
||
<dt> Austronesian family</dt>
|
||
<dd><p>Bahasa Indonesian </p></dd>
|
||
<dt> Artificial</dt>
|
||
<dd><p>Esperanto </p></dd>
|
||
</dl>
|
||
|
||
<p>Other languages using the same header entry are:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Finno-Ugric family</dt>
|
||
<dd><p>Hungarian </p></dd>
|
||
<dt> Turkic/Altaic family</dt>
|
||
<dd><p>Turkish </p></dd>
|
||
</dl>
|
||
|
||
<p>Hungarian does not appear to have a plural if you look at sentences involving
|
||
cardinal numbers. For example, “1 apple” is “1 alma”, and “123 apples” is
|
||
“123 alma”. But when the number is not explicit, the distinction between
|
||
singular and plural exists: “the apple” is “az alma”, and “the apples” is
|
||
“az almák”. Since <code>ngettext</code> has to support both types of sentences,
|
||
it is classified here, under “two forms”.
|
||
</p>
|
||
<p>The same holds for Turkish: “1 apple” is “1 elma”, and “123 apples” is
|
||
“123 elma”. But when the number is omitted, the distinction between singular
|
||
and plural exists: “the apple” is “elma”, and “the apples” is
|
||
“elmalar”.
|
||
</p>
|
||
</dd>
|
||
<dt> Two forms, singular used for zero and one</dt>
|
||
<dd><p>Exceptional case in the language family. The header entry would be:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=2; plural=n>1;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Romanic family</dt>
|
||
<dd><p>Brazilian Portuguese, French </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Three forms, special case for zero</dt>
|
||
<dd><p>The header entry would be:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=3; plural=n%10==1 && n%100!=11 ? 0 : n != 0 ? 1 : 2;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Baltic family</dt>
|
||
<dd><p>Latvian </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Three forms, special cases for one and two</dt>
|
||
<dd><p>The header entry would be:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=3; plural=n==1 ? 0 : n==2 ? 1 : 2;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Celtic</dt>
|
||
<dd><p>Gaeilge (Irish) </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Three forms, special case for numbers ending in 00 or [2-9][0-9]</dt>
|
||
<dd><p>The header entry would be:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=3; \
|
||
plural=n==1 ? 0 : (n==0 || (n%100 > 0 && n%100 < 20)) ? 1 : 2;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Romanic family</dt>
|
||
<dd><p>Romanian </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Three forms, special case for numbers ending in 1[2-9]</dt>
|
||
<dd><p>The header entry would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=3; \
|
||
plural=n%10==1 && n%100!=11 ? 0 : \
|
||
n%10>=2 && (n%100<10 || n%100>=20) ? 1 : 2;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Baltic family</dt>
|
||
<dd><p>Lithuanian </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Three forms, special cases for numbers ending in 1 and 2, 3, 4, except those ending in 1[1-4]</dt>
|
||
<dd><p>The header entry would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=3; \
|
||
plural=n%10==1 && n%100!=11 ? 0 : \
|
||
n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Slavic family</dt>
|
||
<dd><p>Russian, Ukrainian, Belarusian, Serbian, Croatian </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Three forms, special cases for 1 and 2, 3, 4</dt>
|
||
<dd><p>The header entry would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=3; \
|
||
plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Slavic family</dt>
|
||
<dd><p>Czech, Slovak </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Three forms, special case for one and some numbers ending in 2, 3, or 4</dt>
|
||
<dd><p>The header entry would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=3; \
|
||
plural=n==1 ? 0 : \
|
||
n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Slavic family</dt>
|
||
<dd><p>Polish </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Four forms, special case for one and all numbers ending in 02, 03, or 04</dt>
|
||
<dd><p>The header entry would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=4; \
|
||
plural=n%100==1 ? 0 : n%100==2 ? 1 : n%100==3 || n%100==4 ? 2 : 3;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Slavic family</dt>
|
||
<dd><p>Slovenian </p></dd>
|
||
</dl>
|
||
|
||
</dd>
|
||
<dt> Six forms, special cases for one, two, all numbers ending in 02, 03, … 10, all numbers ending in 11 … 99, and others</dt>
|
||
<dd><p>The header entry would look like this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">Plural-Forms: nplurals=6; \
|
||
plural=n==0 ? 0 : n==1 ? 1 : n==2 ? 2 : n%100>=3 && n%100<=10 ? 3 \
|
||
: n%100>=11 ? 4 : 5;
|
||
</pre></td></tr></table>
|
||
|
||
<p>Languages with this property include:
|
||
</p>
|
||
<dl compact="compact">
|
||
<dt> Afroasiatic family</dt>
|
||
<dd><p>Arabic </p></dd>
|
||
</dl>
|
||
</dd>
|
||
</dl>
|
||
|
||
<p>You might now ask, <code>ngettext</code> handles only numbers <var>n</var> of type
|
||
‘<samp>unsigned long</samp>’. What about larger integer types? What about negative
|
||
numbers? What about floating-point numbers?
|
||
</p>
|
||
<p>About larger integer types, such as ‘<samp>uintmax_t</samp>’ or
|
||
‘<samp>unsigned long long</samp>’: they can be handled by reducing the value to a
|
||
range that fits in an ‘<samp>unsigned long</samp>’. Simply casting the value to
|
||
‘<samp>unsigned long</samp>’ would not do the right thing, since it would treat
|
||
<code>ULONG_MAX + 1</code> like zero, <code>ULONG_MAX + 2</code> like singular, and
|
||
the like. Here you can exploit the fact that all mentioned plural form
|
||
formulas eventually become periodic, with a period that is a divisor of 100
|
||
(or 1000 or 1000000). So, when you reduce a large value to another one in
|
||
the range [1000000, 1999999] that ends in the same 6 decimal digits, you
|
||
can assume that it will lead to the same plural form selection. This code
|
||
does this:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">#include <inttypes.h>
|
||
uintmax_t nbytes = ...;
|
||
printf (ngettext ("The file has %"PRIuMAX" byte.",
|
||
"The file has %"PRIuMAX" bytes.",
|
||
(nbytes > ULONG_MAX
|
||
? (nbytes % 1000000) + 1000000
|
||
: nbytes)),
|
||
nbytes);
|
||
</pre></td></tr></table>
|
||
|
||
<p>Negative and floating-point values usually represent physical entities for
|
||
which singular and plural don't clearly apply. In such cases, there is no
|
||
need to use <code>ngettext</code>; a simple <code>gettext</code> call with a form suitable
|
||
for all values will do. For example:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="smallexample">printf (gettext ("Time elapsed: %.3f seconds"),
|
||
num_milliseconds * 0.001);
|
||
</pre></td></tr></table>
|
||
|
||
<p>Even if <var>num_milliseconds</var> happens to be a multiple of 1000, the output
|
||
</p><table><tr><td> </td><td><pre class="smallexample">Time elapsed: 1.000 seconds
|
||
</pre></td></tr></table>
|
||
<p>is acceptable in English, and similarly for other languages.
|
||
</p>
|
||
<p>The translators' perspective regarding plural forms is explained in
|
||
<a href="gettext_12.html#SEC228">Translating plural forms</a>.
|
||
</p>
|
||
|
||
<a name="Optimized-gettext"></a>
|
||
<a name="SEC208"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC201">11.2.7 Optimization of the *gettext functions</a> </h3>
|
||
|
||
<p>At this point of the discussion we should talk about an advantage of the
|
||
GNU <code>gettext</code> implementation. Some readers might have pointed out
|
||
that an internationalized program might have a poor performance if some
|
||
string has to be translated in an inner loop. While this is unavoidable
|
||
when the string varies from one run of the loop to the other it is
|
||
simply a waste of time when the string is always the same. Take the
|
||
following example:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">{
|
||
while (…)
|
||
{
|
||
puts (gettext ("Hello world"));
|
||
}
|
||
}
|
||
</pre></td></tr></table>
|
||
|
||
<p>When the locale selection does not change between two runs the resulting
|
||
string is always the same. One way to use this is:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">{
|
||
str = gettext ("Hello world");
|
||
while (…)
|
||
{
|
||
puts (str);
|
||
}
|
||
}
|
||
</pre></td></tr></table>
|
||
|
||
<p>But this solution is not usable in all situation (e.g. when the locale
|
||
selection changes) nor does it lead to legible code.
|
||
</p>
|
||
<p>For this reason, GNU <code>gettext</code> caches previous translation results.
|
||
When the same translation is requested twice, with no new message
|
||
catalogs being loaded in between, <code>gettext</code> will, the second time,
|
||
find the result through a single cache lookup.
|
||
</p>
|
||
|
||
<a name="Comparison"></a>
|
||
<a name="SEC209"></a>
|
||
<h2 class="section"> <a href="gettext_toc.html#TOC202">11.3 Comparing the Two Interfaces</a> </h2>
|
||
|
||
|
||
<p>The following discussion is perhaps a little bit colored. As said
|
||
above we implemented GNU <code>gettext</code> following the Uniforum
|
||
proposal and this surely has its reasons. But it should show how we
|
||
came to this decision.
|
||
</p>
|
||
<p>First we take a look at the developing process. When we write an
|
||
application using NLS provided by <code>gettext</code> we proceed as always.
|
||
Only when we come to a string which might be seen by the users and thus
|
||
has to be translated we use <code>gettext("…")</code> instead of
|
||
<code>"…"</code>. At the beginning of each source file (or in a central
|
||
header file) we define
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">#define gettext(String) (String)
|
||
</pre></td></tr></table>
|
||
|
||
<p>Even this definition can be avoided when the system supports the
|
||
<code>gettext</code> function in its C library. When we compile this code the
|
||
result is the same as if no NLS code is used. When you take a look at
|
||
the GNU <code>gettext</code> code you will see that we use <code>_("…")</code>
|
||
instead of <code>gettext("…")</code>. This reduces the number of
|
||
additional characters per translatable string to <em>3</em> (in words:
|
||
three).
|
||
</p>
|
||
<p>When now a production version of the program is needed we simply replace
|
||
the definition
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">#define _(String) (String)
|
||
</pre></td></tr></table>
|
||
|
||
<p>by
|
||
</p>
|
||
<a name="IDX1076"></a>
|
||
<table><tr><td> </td><td><pre class="example">#include <libintl.h>
|
||
#define _(String) gettext (String)
|
||
</pre></td></tr></table>
|
||
|
||
<p>Additionally we run the program ‘<tt>xgettext</tt>’ on all source code file
|
||
which contain translatable strings and that's it: we have a running
|
||
program which does not depend on translations to be available, but which
|
||
can use any that becomes available.
|
||
</p>
|
||
<a name="IDX1077"></a>
|
||
<p>The same procedure can be done for the <code>gettext_noop</code> invocations
|
||
(see section <a href="gettext_4.html#SEC31">Special Cases of Translatable Strings</a>). One usually defines <code>gettext_noop</code> as a
|
||
no-op macro. So you should consider the following code for your project:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">#define gettext_noop(String) String
|
||
#define N_(String) gettext_noop (String)
|
||
</pre></td></tr></table>
|
||
|
||
<p><code>N_</code> is a short form similar to <code>_</code>. The ‘<tt>Makefile</tt>’ in
|
||
the ‘<tt>po/</tt>’ directory of GNU <code>gettext</code> knows by default both of the
|
||
mentioned short forms so you are invited to follow this proposal for
|
||
your own ease.
|
||
</p>
|
||
<p>Now to <code>catgets</code>. The main problem is the work for the
|
||
programmer. Every time he comes to a translatable string he has to
|
||
define a number (or a symbolic constant) which has also be defined in
|
||
the message catalog file. He also has to take care for duplicate
|
||
entries, duplicate message IDs etc. If he wants to have the same
|
||
quality in the message catalog as the GNU <code>gettext</code> program
|
||
provides he also has to put the descriptive comments for the strings and
|
||
the location in all source code files in the message catalog. This is
|
||
nearly a Mission: Impossible.
|
||
</p>
|
||
<p>But there are also some points people might call advantages speaking for
|
||
<code>catgets</code>. If you have a single word in a string and this string
|
||
is used in different contexts it is likely that in one or the other
|
||
language the word has different translations. Example:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">printf ("%s: %d", gettext ("number"), number_of_errors)
|
||
|
||
printf ("you should see %d %s", number_count,
|
||
number_count == 1 ? gettext ("number") : gettext ("numbers"))
|
||
</pre></td></tr></table>
|
||
|
||
<p>Here we have to translate two times the string <code>"number"</code>. Even
|
||
if you do not speak a language beside English it might be possible to
|
||
recognize that the two words have a different meaning. In German the
|
||
first appearance has to be translated to <code>"Anzahl"</code> and the second
|
||
to <code>"Zahl"</code>.
|
||
</p>
|
||
<p>Now you can say that this example is really esoteric. And you are
|
||
right! This is exactly how we felt about this problem and decide that
|
||
it does not weight that much. The solution for the above problem could
|
||
be very easy:
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example">printf ("%s %d", gettext ("number:"), number_of_errors)
|
||
|
||
printf (number_count == 1 ? gettext ("you should see %d number")
|
||
: gettext ("you should see %d numbers"),
|
||
number_count)
|
||
</pre></td></tr></table>
|
||
|
||
<p>We believe that we can solve all conflicts with this method. If it is
|
||
difficult one can also consider changing one of the conflicting string a
|
||
little bit. But it is not impossible to overcome.
|
||
</p>
|
||
<p><code>catgets</code> allows same original entry to have different translations,
|
||
but <code>gettext</code> has another, scalable approach for solving ambiguities
|
||
of this kind: See section <a href="#SEC203">Solving Ambiguities</a>.
|
||
</p>
|
||
|
||
<a name="Using-libintl_002ea"></a>
|
||
<a name="SEC210"></a>
|
||
<h2 class="section"> <a href="gettext_toc.html#TOC203">11.4 Using libintl.a in own programs</a> </h2>
|
||
|
||
<p>Starting with version 0.9.4 the library <code>libintl.h</code> should be
|
||
self-contained. I.e., you can use it in your own programs without
|
||
providing additional functions. The ‘<tt>Makefile</tt>’ will put the header
|
||
and the library in directories selected using the <code>$(prefix)</code>.
|
||
</p>
|
||
|
||
<a name="gettext-grok"></a>
|
||
<a name="SEC211"></a>
|
||
<h2 class="section"> <a href="gettext_toc.html#TOC204">11.5 Being a <code>gettext</code> grok</a> </h2>
|
||
|
||
<p><strong> NOTE: </strong> This documentation section is outdated and needs to be
|
||
revised.
|
||
</p>
|
||
<p>To fully exploit the functionality of the GNU <code>gettext</code> 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:
|
||
</p>
|
||
<ul>
|
||
<li> Changing the language at runtime
|
||
<a name="IDX1078"></a>
|
||
|
||
<p>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 <code>gettext</code>
|
||
function. The method which is presented here only works correctly
|
||
with the GNU implementation of the <code>gettext</code> functions.
|
||
</p>
|
||
<p>In the function <code>dcgettext</code> 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:
|
||
</p>
|
||
<ol>
|
||
<li><a name="IDX1079"></a>
|
||
</li><li> <code>LANGUAGE</code>
|
||
<a name="IDX1080"></a>
|
||
</li><li> <code>LC_ALL</code>
|
||
<a name="IDX1081"></a>
|
||
<a name="IDX1082"></a>
|
||
<a name="IDX1083"></a>
|
||
<a name="IDX1084"></a>
|
||
<a name="IDX1085"></a>
|
||
<a name="IDX1086"></a>
|
||
</li><li> <code>LC_xxx</code>, according to selected locale category
|
||
<a name="IDX1087"></a>
|
||
</li><li> <code>LANG</code>
|
||
</li></ol>
|
||
|
||
<p>Afterwards the path is constructed using the found value and the
|
||
translation file is loaded if available.
|
||
</p>
|
||
<p>What happens now when the value for, say, <code>LANGUAGE</code> changes? According
|
||
to the process explained above the new value of this variable is found
|
||
as soon as the <code>dcgettext</code> function is called. But this also means
|
||
the (perhaps) different message catalog file is loaded. In other
|
||
words: the used language is changed.
|
||
</p>
|
||
<p>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 <code>dcgettext</code> function as long as no new catalog is loaded. But
|
||
if <code>dcgettext</code> is not called the program also cannot find the
|
||
<code>LANGUAGE</code> variable be changed (see section <a href="#SEC208">Optimization of the *gettext functions</a>). A
|
||
solution for this is very easy. Include the following code in the
|
||
language switching function.
|
||
</p>
|
||
<table><tr><td> </td><td><pre class="example"> /* Change language. */
|
||
setenv ("LANGUAGE", "fr", 1);
|
||
|
||
/* Make change known. */
|
||
{
|
||
extern int _nl_msg_cat_cntr;
|
||
++_nl_msg_cat_cntr;
|
||
}
|
||
</pre></td></tr></table>
|
||
|
||
<a name="IDX1088"></a>
|
||
<p>The variable <code>_nl_msg_cat_cntr</code> is defined in ‘<tt>loadmsgcat.c</tt>’.
|
||
You don't need to know what this is for. But it can be used to detect
|
||
whether a <code>gettext</code> implementation is GNU gettext and not non-GNU
|
||
system's native gettext implementation.
|
||
</p>
|
||
</li></ul>
|
||
|
||
|
||
<a name="Temp-Programmers"></a>
|
||
<a name="SEC212"></a>
|
||
<h2 class="section"> <a href="gettext_toc.html#TOC205">11.6 Temporary Notes for the Programmers Chapter</a> </h2>
|
||
|
||
<p><strong> NOTE: </strong> This documentation section is outdated and needs to be
|
||
revised.
|
||
</p>
|
||
|
||
|
||
<a name="Temp-Implementations"></a>
|
||
<a name="SEC213"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC206">11.6.1 Temporary - Two Possible Implementations</a> </h3>
|
||
|
||
<p>There are two competing methods for language independent messages:
|
||
the X/Open <code>catgets</code> method, and the Uniforum <code>gettext</code>
|
||
method. The <code>catgets</code> method indexes messages by integers; the
|
||
<code>gettext</code> method indexes them by their English translations.
|
||
The <code>catgets</code> method has been around longer and is supported
|
||
by more vendors. The <code>gettext</code> method is supported by Sun,
|
||
and it has been heard that the COSE multi-vendor initiative is
|
||
supporting it. Neither method is a POSIX standard; the POSIX.1
|
||
committee had a lot of disagreement in this area.
|
||
</p>
|
||
<p>Neither one is in the POSIX standard. There was much disagreement
|
||
in the POSIX.1 committee about using the <code>gettext</code> routines
|
||
vs. <code>catgets</code> (XPG). In the end the committee couldn't
|
||
agree on anything, so no messaging system was included as part
|
||
of the standard. I believe the informative annex of the standard
|
||
includes the XPG3 messaging interfaces, “…as an example of
|
||
a messaging system that has been implemented…”
|
||
</p>
|
||
<p>They were very careful not to say anywhere that you should use one
|
||
set of interfaces over the other. For more on this topic please
|
||
see the Programming for Internationalization FAQ.
|
||
</p>
|
||
|
||
<a name="Temp-catgets"></a>
|
||
<a name="SEC214"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC207">11.6.2 Temporary - About <code>catgets</code></a> </h3>
|
||
|
||
<p>There have been a few discussions of late on the use of
|
||
<code>catgets</code> as a base. I think it important to present both
|
||
sides of the argument and hence am opting to play devil's advocate
|
||
for a little bit.
|
||
</p>
|
||
<p>I'll not deny the fact that <code>catgets</code> could have been designed
|
||
a lot better. It currently has quite a number of limitations and
|
||
these have already been pointed out.
|
||
</p>
|
||
<p>However there is a great deal to be said for consistency and
|
||
standardization. A common recurring problem when writing Unix
|
||
software is the myriad portability problems across Unix platforms.
|
||
It seems as if every Unix vendor had a look at the operating system
|
||
and found parts they could improve upon. Undoubtedly, these
|
||
modifications are probably innovative and solve real problems.
|
||
However, software developers have a hard time keeping up with all
|
||
these changes across so many platforms.
|
||
</p>
|
||
<p>And this has prompted the Unix vendors to begin to standardize their
|
||
systems. Hence the impetus for Spec1170. Every major Unix vendor
|
||
has committed to supporting this standard and every Unix software
|
||
developer waits with glee the day they can write software to this
|
||
standard and simply recompile (without having to use autoconf)
|
||
across different platforms.
|
||
</p>
|
||
<p>As I understand it, Spec1170 is roughly based upon version 4 of the
|
||
X/Open Portability Guidelines (XPG4). Because <code>catgets</code> and
|
||
friends are defined in XPG4, I'm led to believe that <code>catgets</code>
|
||
is a part of Spec1170 and hence will become a standardized component
|
||
of all Unix systems.
|
||
</p>
|
||
|
||
<a name="Temp-WSI"></a>
|
||
<a name="SEC215"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC208">11.6.3 Temporary - Why a single implementation</a> </h3>
|
||
|
||
<p>Now it seems kind of wasteful to me to have two different systems
|
||
installed for accessing message catalogs. If we do want to remedy
|
||
<code>catgets</code> deficiencies why don't we try to expand <code>catgets</code>
|
||
(in a compatible manner) rather than implement an entirely new system.
|
||
Otherwise, we'll end up with two message catalog access systems installed
|
||
with an operating system - one set of routines for packages using GNU
|
||
<code>gettext</code> for their internationalization, and another set of routines
|
||
(catgets) for all other software. Bloated?
|
||
</p>
|
||
<p>Supposing another catalog access system is implemented. Which do
|
||
we recommend? At least for Linux, we need to attract as many
|
||
software developers as possible. Hence we need to make it as easy
|
||
for them to port their software as possible. Which means supporting
|
||
<code>catgets</code>. We will be implementing the <code>libintl</code> code
|
||
within our <code>libc</code>, but does this mean we also have to incorporate
|
||
another message catalog access scheme within our <code>libc</code> as well?
|
||
And what about people who are going to be using the <code>libintl</code>
|
||
+ non-<code>catgets</code> routines. When they port their software to
|
||
other platforms, they're now going to have to include the front-end
|
||
(<code>libintl</code>) code plus the back-end code (the non-<code>catgets</code>
|
||
access routines) with their software instead of just including the
|
||
<code>libintl</code> code with their software.
|
||
</p>
|
||
<p>Message catalog support is however only the tip of the iceberg.
|
||
What about the data for the other locale categories? They also have
|
||
a number of deficiencies. Are we going to abandon them as well and
|
||
develop another duplicate set of routines (should <code>libintl</code>
|
||
expand beyond message catalog support)?
|
||
</p>
|
||
<p>Like many parts of Unix that can be improved upon, we're stuck with balancing
|
||
compatibility with the past with useful improvements and innovations for
|
||
the future.
|
||
</p>
|
||
|
||
<a name="Temp-Notes"></a>
|
||
<a name="SEC216"></a>
|
||
<h3 class="subsection"> <a href="gettext_toc.html#TOC209">11.6.4 Temporary - Notes</a> </h3>
|
||
|
||
<p>X/Open agreed very late on the standard form so that many
|
||
implementations differ from the final form. Both of my system (old
|
||
Linux catgets and Ultrix-4) have a strange variation.
|
||
</p>
|
||
<p>OK. After incorporating the last changes I have to spend some time on
|
||
making the GNU/Linux <code>libc</code> <code>gettext</code> functions. So in future
|
||
Solaris is not the only system having <code>gettext</code>.
|
||
</p>
|
||
|
||
<table cellpadding="1" cellspacing="1" border="0">
|
||
<tr><td valign="middle" align="left">[<a href="#SEC197" title="Beginning of this chapter or previous chapter"> << </a>]</td>
|
||
<td valign="middle" align="left">[<a href="gettext_12.html#SEC217" title="Next chapter"> >> </a>]</td>
|
||
<td valign="middle" align="left"> </td>
|
||
<td valign="middle" align="left"> </td>
|
||
<td valign="middle" align="left"> </td>
|
||
<td valign="middle" align="left"> </td>
|
||
<td valign="middle" align="left"> </td>
|
||
<td valign="middle" align="left">[<a href="gettext_toc.html#SEC_Top" title="Cover (top) of document">Top</a>]</td>
|
||
<td valign="middle" align="left">[<a href="gettext_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
|
||
<td valign="middle" align="left">[<a href="gettext_21.html#SEC389" title="Index">Index</a>]</td>
|
||
<td valign="middle" align="left">[<a href="gettext_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
|
||
</tr></table>
|
||
<p>
|
||
<font size="-1">
|
||
This document was generated by <em>Bruno Haible</em> on <em>February, 21 2024</em> using <a href="https://www.nongnu.org/texi2html/"><em>texi2html 1.78a</em></a>.
|
||
</font>
|
||
<br>
|
||
|
||
</p>
|
||
</body>
|
||
</html>
|