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4.7 KiB
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77 lines
4.7 KiB
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<HTML>
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<TITLE>Creating and Using Streams Instantiated on User-Defined Types</TITLE>
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<A HREF="41-2.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="42.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library User's Guide</B></DIV>
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<H2>41.3 Creating and Using Streams Instantiated on User-Defined Types</H2>
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<A NAME="idx971"><!></A>
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<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>
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<UL><PRE>
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typedef std::basic_fstream<Echar,Etraits> Estream; // 1
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std::locale Eloc(std::locale(std::locale(),
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new Ecodecvt),new Ectype); // 2
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Estream foo("foo.txt"); // 3
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foo.imbue(Eloc); // 4
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</PRE></UL>
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<TABLE CELLPADDING="3">
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<TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>Typedef the special stream type to something convenient.
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<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.
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<TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>Construct an <SAMP>Estream</SAMP>.
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<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>.
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</TABLE>
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<P>Now we're ready to insert <SAMP>Echar</SAMP>s into the stream and read them back in:</P>
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<UL><PRE>
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Echar e[10];
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Estream::pos_type pos = foo.tellp(); //1
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foo << 10; //2
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foo.seekg(pos); //3
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foo >> e; //4
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</PRE></UL>
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<TABLE CELLPADDING="3">
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<TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>Get current position.
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<TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>Write out the integer <SAMP>10</SAMP>.
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<TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>Seek back.
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<TR VALIGN="top"><TD><SAMP>//4</SAMP></TD><TD>Read in the string <SAMP>10</SAMP> as <SAMP>Echar</SAMP>s.
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</TABLE>
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