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| <TITLE>A Phone Number Formatting Facet Class</TITLE> |
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| <H2>26.3 A Phone Number Formatting Facet Class</H2> |
| <P>Now that we have locales and facets in C++, we can encapsulate the locale-dependent parsing and formatting of telephone numbers into a new facet class. Let's focus on formatting in this example. We call the new facet class <SAMP>phone_put</SAMP>, analogous to <SAMP>time_put</SAMP>, <SAMP>money_put</SAMP>, etc.</P> |
| <A NAME="idx589"><!></A> |
| <P>The <SAMP>phone_put</SAMP> facet class serves solely as a base class for facet classes that actually implement the locale-dependent formatting. The relationship of class <SAMP>phone_put</SAMP> to the other facet classes is illustrated in <A HREF="26-3.html#Figure 13">Figure 13</A>:</P> |
| <A NAME="idx590"><!></A> |
| <H4><A NAME="Figure 13">Figure 13: The relationship of the phone_put facet to the implementing facets</A></H4> |
| |
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| <P>Here is a first tentative declaration of the new facet class <SAMP>phone_put</SAMP>:</P> |
| |
| <UL><PRE> |
| class phone_put: public std::locale::facet { // 1 |
| public: |
| static std::locale::id id; // 2 |
| typedef std::string string_type; |
| |
| phone_put (std::size_t refs = 0) |
| : std::locale::facet (refs) { } // 3 |
| |
| string_type put (const string_type &cntryName, |
| const string_type &areaCode, |
| const string_type &extension) const; // 4 |
| }; |
| |
| </PRE></UL> |
| <TABLE CELLPADDING="3"> |
| |
| <TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>Derive from the base class <SAMP>std::locale::facet</SAMP>, so that a locale object is able to maintain instances of our new phone facet class. |
| <TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>New base facet classes need to define a static data member <SAMP>id</SAMP> of type <SAMP>std::locale::id</SAMP>. |
| <TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>Define a constructor that takes the reference count that is handed over to the base class. |
| <TR VALIGN="top"><TD><SAMP>//4</SAMP></TD><TD>Define a function <SAMP>put()</SAMP> that does the actual formatting. |
| </TABLE> |
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