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<TITLE>The C Locale</TITLE>
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<H2>24.1 The C Locale</H2>
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<P>All the culture and language dependencies discussed in the previous section need to be represented in an operating system. This information is usually represented in a kind of language table, called a <I>locale</I>.</P>
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<P>The X/Open consortium has standardized a variety of services for Native Language Support (NLS<I>)</I> in the programming language C. This standard is commonly known as XPG4. Internationalization services as well as localization support are included in X/Open's <I>Native Language Support</I>. The description below is based on this standard.</P>
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<P>According to XPG4, the C locale is composed of several <I>categories</I>, which are given in <A HREF="24-1.html#Table&nbsp;24">Table&nbsp;24</A>.</P>
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<H4><A NAME="Table&nbsp;24">Table&nbsp;24: Categories of the C locale&nbsp;</A></H4>
<TABLE BORDER="1" CELLPADDING="3" CELLSPACING="3">
<tr><td valign=top><B>Category</B>
</td><td valign=top><B>Content</B>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>LC_NUMERIC</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Rules and symbols for numbers</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>LC_TIME</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Values for date and time information</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>LC_MONETARY</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Rules and symbols for monetary information</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>LC_CTYPE</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Character classification and case conversion</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>LC_COLLATE</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Collation sequence</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>LC_MESSAGES</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Formats and values of messages</P>
</td></tr>
</TABLE>
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<P>The external representation of a C locale is usually a <I>file</I> in UNIX. Other operating systems may use other representations. The external representation is transformed into an internal memory representation by calling the function <SAMP>setlocale()</SAMP>, as shown in <A HREF="24-1.html#Figure&nbsp;4">Figure&nbsp;4</A>:</P>
<H4><A NAME="Figure&nbsp;4">Figure&nbsp;4: Transformation of a C locale from external to internal representation</A></H4>

<P><IMG SRC="images/locfig4.gif" WIDTH=583 HEIGHT=302></P>
<P>Inside a program, the C locale is represented by one or more global data structures. The C library provides a set of functions that use information from those global data structures to adapt their behavior to local conventions. Examples of these functions and the information they cover are listed in <A HREF="24-1.html#Table&nbsp;25">Table&nbsp;25</A>:</P>
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<H4><A NAME="Table&nbsp;25">Table&nbsp;25: C locale functions and the information they cover&nbsp;</A></H4>
<TABLE BORDER="1" CELLPADDING="3" CELLSPACING="3">
<tr><td valign=top><B>C Locale Function</B>
</td><td valign=top><B>Information Covered</B>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>setlocale()</SAMP>, ...</P>
</td><td valign=top><P CLASS="TABLE">Locale initialization and </P>
<P CLASS="TABLE">language information</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>isalpha()</SAMP>, <SAMP>isupper()</SAMP>, <SAMP>isdigit()</SAMP>, ...</P>
</td><td valign=top><P CLASS="TABLE">Character classification</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>strftime()</SAMP>, ...</P>
</td><td valign=top><P CLASS="TABLE">Date and time functions</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>strfmon()</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Monetary functions</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>printf(), scanf()</SAMP>, ...</P>
</td><td valign=top><P CLASS="TABLE">Number parsing and formatting</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>strcoll()</SAMP>, <SAMP>wcscoll()</SAMP>, ...</P>
</td><td valign=top><P CLASS="TABLE">String collation</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>mblen()</SAMP>, <SAMP>mbtowc()</SAMP>, <SAMP>wctomb()</SAMP>, ...</P>
</td><td valign=top><P CLASS="TABLE">Multibyte functions</P>
</td></tr>
<tr><td valign=top><P CLASS="TABLE"><SAMP>catopen()</SAMP>, <SAMP>catgets()</SAMP>, <SAMP>catclose()</SAMP></P>
</td><td valign=top><P CLASS="TABLE">Message retrieval</P>
</td></tr>
</TABLE>

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