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 <H2>32.3 A Simple Extractor and Inserter for the Example</H2>
 <P>Following the read and write conventions of iostreams, we would insert and extract the date object like this:</P>

 <UL><PRE>
 date birthday(2,6,1952);
 std::cout &lt;&lt; birthday &lt;&lt; '\n';
 </PRE></UL>
 <P>or </P>

 <UL><PRE>
 date aDate;

 std::cout &lt;&lt; '\n' &lt;&lt; "Please, enter a date (day month year)"
           &lt;&lt; '\n';
 std::cin  &gt;&gt; aDate;
 std::cout &lt;&lt; aDate &lt;&lt; '\n';
 </PRE></UL>
 <A NAME="idx781"><!></A>
 <P>For the next step, we would implement shift operators as inserters and extractors for <SAMP>date</SAMP> objects. Here is an extractor for class <SAMP>date</SAMP>:</P>

 <UL><PRE>
 template&lt;class charT, class Traits&gt;
 std::basic_istream&lt;charT, Traits&gt;&amp;                            //1
 operator&gt;&gt; (std::basic_istream&lt;charT,Traits&gt;&amp; is,             //2
             date&amp; dat)                                        //3
 {
   is &gt;&gt; dat.tm_date.tm_mday;                                  //4
   is &gt;&gt; dat.tm_date.tm_mon;
   is &gt;&gt; dat.tm_date.tm_year;
   return is;                                                  //5
 }
 </PRE></UL>
 <TABLE CELLPADDING="3">

 <TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>The returned value for extractors (and inserters) is a reference to the stream, so that several extractions can be done in one expression.
 <TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>The first parameter usually is the stream from which the data shall be extracted.
 <TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>The second parameter is a reference, or alternatively a pointer, to an object of the user-defined type.
 <TR VALIGN="top"><TD><SAMP>//4</SAMP></TD><TD>In order to allow access to private data of the date class, the extractor must be declared as a friend function in class <SAMP>date</SAMP>.
 <TR VALIGN="top"><TD><SAMP>//5</SAMP></TD><TD>The return value is the stream from which the data was extracted.
 </TABLE>
 <A NAME="idx782"><!></A>
 <P>As the extractor accesses private data members of class date, it must be declared as a friend function to class date. The same holds for the inserter. Here's a more complete version of class <SAMP>date</SAMP>:</P>

 <UL><PRE>
 class date {
 public:
   date(int d, int m, int y);
   date(tm t);
   date();
   // more constructors and useful member functions

 private:
   std::tm tm_date;

   template&lt;class charT, Traits&gt;
   friend std::basic_istream&lt;charT, Traits&gt;
   &amp;operator &gt;&gt;(std::basic_istream&lt;charT, Traits &gt;&amp; is, date&amp; dat);

   template&lt;class charT, Traits&gt;
   friend std::basic_ostream&lt;charT, Traits&gt;
   &amp;operator &lt;&lt;(std::basic_ostream&lt;charT, Traits &gt;&amp; os,
                const date&amp; dat);
 };
 </PRE></UL>
 <A NAME="idx783"><!></A>
 <P>The inserter can be built analogously, as shown below. The only difference is that you would hand over a <I>constant</I> reference to a date object, because the inserter is not supposed to modify the object it prints.</P>

 <UL><PRE>
 template&lt;class charT, class Traits&gt;
 std::basic_ostream&lt;charT, Traits&gt;&amp;
 operator &lt;&lt; (std::basic_ostream&lt;charT, Traits &gt;&amp; os,
              const date&amp; dat)
 {
   os &lt;&lt; dat.tm_date.tm_mon &lt;&lt; '-';
   os &lt;&lt; dat.tm_date.tm_mday &lt;&lt; '-';
   os &lt;&lt; dat.tm_date.tm_year ;
   return os;
 }
 </PRE></UL>

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	<H2>32.3 A Simple Extractor and Inserter for the Example</H2>
	<P>Following the read and write conventions of iostreams, we would insert and extract the date object like this:</P>

	<UL><PRE>
	date birthday(2,6,1952);
	std::cout << birthday << '\n';
	</PRE></UL>
	<P>or </P>

	<UL><PRE>
	date aDate;

	std::cout << '\n' << "Please, enter a date (day month year)"
	<< '\n';
	std::cin >> aDate;
	std::cout << aDate << '\n';
	</PRE></UL>
	<A NAME="idx781"><!></A>
	<P>For the next step, we would implement shift operators as inserters and extractors for <SAMP>date</SAMP> objects. Here is an extractor for class <SAMP>date</SAMP>:</P>

	<UL><PRE>
	template<class charT, class Traits>
	std::basic_istream<charT, Traits>& //1
	operator>> (std::basic_istream<charT,Traits>& is, //2
	date& dat) //3
	{
	is >> dat.tm_date.tm_mday; //4
	is >> dat.tm_date.tm_mon;
	is >> dat.tm_date.tm_year;
	return is; //5
	}
	</PRE></UL>
	<TABLE CELLPADDING="3">

	<TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>The returned value for extractors (and inserters) is a reference to the stream, so that several extractions can be done in one expression.
	<TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>The first parameter usually is the stream from which the data shall be extracted.
	<TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>The second parameter is a reference, or alternatively a pointer, to an object of the user-defined type.
	<TR VALIGN="top"><TD><SAMP>//4</SAMP></TD><TD>In order to allow access to private data of the date class, the extractor must be declared as a friend function in class <SAMP>date</SAMP>.
	<TR VALIGN="top"><TD><SAMP>//5</SAMP></TD><TD>The return value is the stream from which the data was extracted.
	</TABLE>
	<A NAME="idx782"><!></A>
	<P>As the extractor accesses private data members of class date, it must be declared as a friend function to class date. The same holds for the inserter. Here's a more complete version of class <SAMP>date</SAMP>:</P>

	<UL><PRE>
	class date {
	public:
	date(int d, int m, int y);
	date(tm t);
	date();
	// more constructors and useful member functions

	private:
	std::tm tm_date;

	template<class charT, Traits>
	friend std::basic_istream<charT, Traits>
	&operator >>(std::basic_istream<charT, Traits >& is, date& dat);

	template<class charT, Traits>
	friend std::basic_ostream<charT, Traits>
	&operator <<(std::basic_ostream<charT, Traits >& os,
	const date& dat);
	};
	</PRE></UL>
	<A NAME="idx783"><!></A>
	<P>The inserter can be built analogously, as shown below. The only difference is that you would hand over a <I>constant</I> reference to a date object, because the inserter is not supposed to modify the object it prints.</P>

	<UL><PRE>
	template<class charT, class Traits>
	std::basic_ostream<charT, Traits>&
	operator << (std::basic_ostream<charT, Traits >& os,
	const date& dat)
	{
	os << dat.tm_date.tm_mon << '-';
	os << dat.tm_date.tm_mday << '-';
	os << dat.tm_date.tm_year ;
	return os;
	}
	</PRE></UL>

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