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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<Echar,Etraits> 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 << 10; //2 |
| foo.seekg(pos); //3 |
| foo >> 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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