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<TITLE>Creating and Using Streams Instantiated on User-Defined Types</TITLE>
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<H2>41.3 Creating and Using Streams Instantiated on User-Defined Types</H2>
<A NAME="idx971"><!></A>
<P>Once all the support work is finished, you can instantiate a stream class template on your type and begin to use it--well, not quite. Because the new stream requires the new facets you've defined, you must first create a new locale containing these facets and then imbue that locale on your stream. You can do this as follows:</P>

<UL><PRE>
typedef std::basic_fstream&lt;Echar,Etraits&gt; Estream;           // 1
std::locale Eloc(std::locale(std::locale(),
                             new Ecodecvt),new Ectype);      // 2
Estream foo("foo.txt");                                      // 3
foo.imbue(Eloc);                                             // 4
</PRE></UL>
<TABLE CELLPADDING="3">

<TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>Typedef the special stream type to something convenient.
<TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>Construct a new locale object and replace the <SAMP>std::codecvt</SAMP> and <SAMP>std::ctype</SAMP> facets with the ones we've defined for <SAMP>Echar</SAMP>. We use the constructor that takes an existing locale and a new facet to construct a locale with a new <SAMP>codecvt</SAMP> facet, and then use it again to get a <SAMP>locale</SAMP> with both new facets.
<TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>Construct an <SAMP>Estream</SAMP>.
<TR VALIGN="top"><TD><SAMP>//4</SAMP></TD><TD>Imbue the new <SAMP>locale</SAMP> object containing our replacement facets onto the <SAMP>Estream</SAMP>.
</TABLE>
<P>Now we're ready to insert <SAMP>Echar</SAMP>s into the stream and read them back in:</P>

<UL><PRE>
Echar e[10];
Estream::pos_type pos = foo.tellp();                           //1
foo &lt;&lt; 10;                                                     //2
foo.seekg(pos);                                                //3
foo &gt;&gt; e;                                                      //4
</PRE></UL>
<TABLE CELLPADDING="3">

<TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>Get current position.
<TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>Write out the integer <SAMP>10</SAMP>.
<TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>Seek back.
<TR VALIGN="top"><TD><SAMP>//4</SAMP></TD><TD>Read in the string <SAMP>10</SAMP> as <SAMP>Echar</SAMP>s. 
</TABLE>

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