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<title>Issue 217: Facets example (Classifying Japanese characters) contains errors</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#TC1">TC1</a> status.</em></p>
<h3 id="217"><a href="lwg-defects.html#217">217</a>. Facets example (Classifying Japanese characters) contains errors</h3>
<p><b>Section:</b> 99 [facets.examples] <b>Status:</b> <a href="lwg-active.html#TC1">TC1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2000-02-29 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#facets.examples">issues</a> in [facets.examples].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TC1">TC1</a> status.</p>
<p><b>Discussion:</b></p>
<p>The example in 22.2.8, paragraph 11 contains the following errors:</p>
<p>1) The member function `My::JCtype::is_kanji()' is non-const; the function
must be const in order for it to be callable on a const object (a reference to
which which is what std::use_facet&lt;&gt;() returns).</p>
<p>2) In file filt.C, the definition of `JCtype::id' must be qualified with the
name of the namespace `My'.</p>
<p>3) In the definition of `loc' and subsequently in the call to use_facet&lt;&gt;()
in main(), the name of the facet is misspelled: it should read `My::JCtype'
rather than `My::JCType'.</p>


<p id="res-217"><b>Proposed resolution:</b></p>
<p>Replace the &quot;Classifying Japanese characters&quot; example in 22.2.8,
paragraph 11 with the following:</p>
<pre>#include &lt;locale&gt;</pre>
<pre>namespace My {
    using namespace std;
    class JCtype : public locale::facet {
    public:
        static locale::id id;     //  required for use as a new locale facet
        bool is_kanji (wchar_t c) const;
        JCtype() {}
    protected:
        ~JCtype() {}
    };
}</pre>
<pre>//  file:  filt.C
#include &lt;iostream&gt;
#include &lt;locale&gt;
#include &quot;jctype&quot;                 //  above
std::locale::id My::JCtype::id;   //  the static  JCtype  member
declared above.</pre>
<pre>int main()
{
    using namespace std;
    typedef ctype&lt;wchar_t&gt; wctype;
    locale loc(locale(&quot;&quot;),              //  the user's preferred locale...
               new My::JCtype);         //  and a new feature ...
    wchar_t c = use_facet&lt;wctype&gt;(loc).widen('!');
    if (!use_facet&lt;My::JCtype&gt;(loc).is_kanji(c))
        cout &lt;&lt; &quot;no it isn't!&quot; &lt;&lt; endl;
    return 0;
}</pre>




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