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extern/stdcxx/4.2.1/doc/stdlibref/bind1st.html
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extern/stdcxx/4.2.1/doc/stdlibref/bind1st.html
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<HTML>
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<HEAD>
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<TITLE>bind1st(), bind2nd(), binder1st, binder2nd</TITLE>
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<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
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<BODY BGCOLOR=#FFFFFF>
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<A HREF="binary-search.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="bitmasktypes.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
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<H2>bind1st(), bind2nd(), binder1st, binder2nd</H2>
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<P><B>Library:</B> <A HREF="2-4.html">General utilities</A></P>
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<PRE><HR><B><I>Function</I></B><HR></PRE>
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<UL>
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<LI><A HREF="#sec1">Local Index</A></LI>
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<LI><A HREF="#sec2">Summary</A></LI>
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<LI><A HREF="#sec3">Synopsis</A></LI>
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<LI><A HREF="#sec4">Description</A></LI>
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<LI><A HREF="#sec5">Interface</A></LI>
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<LI><A HREF="#sec6">Example</A></LI>
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<LI><A HREF="#sec7">See Also</A></LI>
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<LI><A HREF="#sec8">Standards Conformance</A></LI>
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</UL>
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<A NAME="sec1"><H3>Local Index</H3></A>
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No Entries
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<A NAME="sec2"><H3>Summary</H3></A>
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<P>Templatized utilities to bind values to function objects</P>
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<A NAME="sec3"><H3>Synopsis</H3></A>
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<PRE>#include <functional>
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namespace std {
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template <class Operation>
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class binder1st;
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template <class Operation, class T>
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binder1st<Operation> bind1st(const Operation&, const T&);
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template <class Operation>
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class binder2nd ;
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template <class Operation, class T>
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binder2nd<Operation> bind2nd(const Operation&, const T&);
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}
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</PRE>
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<A NAME="sec4"><H3>Description</H3></A>
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<P>Because so many functions included in the C++ Standard Library take other functions as arguments, the library includes classes that let you build new function objects out of old ones. Both <SAMP><A HREF="bind1st.html">bind1st()</A></SAMP> and <SAMP><A HREF="bind1st.html">bind2nd()</A></SAMP> are functions that take as arguments a binary function object <SAMP>f</SAMP> and a value <SAMP>x,</SAMP> and return, respectively, classes <B><I><A HREF="bind1st.html">binder1st</A></I></B> and <B><I><A HREF="bind1st.html">binder2nd</A></I></B>. The underlying function object must be a subclass of <B><I><A HREF="binary-function.html">binary_function</A></I></B>.</P>
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<P>Class <B><I><A HREF="bind1st.html">binder1st</A></I></B> binds the value to the first argument of the binary function, and <B><I><A HREF="bind1st.html">binder2nd</A></I></B> does the same thing for the second argument of the function. The resulting classes can be used in place of a unary predicate in other function calls.</P>
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<P>For example, you could use the <SAMP><A HREF="count.html">count_if()</A></SAMP> algorithm to count all elements in a <B><I><A HREF="vector.html">vector</A></I></B> that are less than or equal to 7, using the following:</P>
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<UL><PRE>
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vector<int> v;<br>int littleNums;<br>
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count_if(v.begin, v.end, bind1st(greater<int>(),7),
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littleNums)
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</PRE></UL>
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<P>This function adds one to <SAMP>littleNums</SAMP> each time the element is greater than 7.</P>
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<A NAME="sec5"><H3>Interface</H3></A>
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<UL><PRE>namespace std {
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// Class binder1st
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template <class Operation>
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class binder1st
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: public unary_function<typename
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Operation::second_argument_type,
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typename Operation::result_type>
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{
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public:
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binder1st(const Operation&,
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const typename Operation::first_argument_type&);
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typename Operation::result_type
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operator() (const typename
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Operation::second_argument_type&) const;
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};
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// Class binder2nd
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template <class Operation>
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class binder2nd
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: public unary_function<typename
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Operation::first_argument_type,
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typename Operation::result_type>
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{
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public:
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binder2nd(const Operation&,
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const typename Operation::second_argument_type&);
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typename Operation::result_type
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operator()(const typename
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Operation::first_argument_type&) const;
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};
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// Creator bind1st
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template <class Operation, class T>
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binder1st<Operation> bind1st(const Operation&, const T&);
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// Creator bind2nd
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template<class Operation, class T>
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binder2nd <Operation> bind2nd(const Operation&, const T&);
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}
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</PRE></UL>
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<A NAME="sec6"><H3>Example</H3></A>
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<UL><PRE>//
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// binders.cpp
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//
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#include <algorithm> // for find_if
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#include <functional> // for equal_to, bind1st, bind2nd
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#include <iostream> // for cout, endl
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#include <vector> // for vector
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int main ()
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{
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typedef std::vector<int, std::allocator<int> > vector;
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typedef std::equal_to<vector::value_type> equal_to;
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const vector::value_type arr [] = { 1, 2, 3, 4 };
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// Set up a vector.
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vector v1 (arr + 0, arr + sizeof arr / sizeof *arr);
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// Create an 'equal to 3' unary predicate by binding 3 to
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// the equal_to binary predicate.
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std::binder1st<equal_to> equal_to_3 =
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bind1st (equal_to (), 3);
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// Now use this new predicate in a call to find_if.
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vector::iterator it1 = std::find_if (v1.begin (),
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v1.end (),
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equal_to_3);
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// Even better, construct the new predicate on the fly.
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vector::iterator it2 =
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std::find_if (v1.begin (), v1.end (),
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std::bind1st (equal_to (), 3));
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// And now the same thing using bind2nd.
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// Same result since equal_to is commutative.
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vector::iterator it3 =
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std::find_if (v1.begin (), v1.end (),
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std::bind2nd (equal_to (), 3));
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// Output results.
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std::cout << *it1 << " " << *it2 << " "
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<< *it3 << std::endl;
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return 0;
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}
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Program Output:
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3 3 3
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</PRE></UL>
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<UL><PRE></PRE></UL>
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<A NAME="sec7"><H3>See Also</H3></A>
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<P><A HREF="functionobjects.html">Function Objects</A></P>
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<A NAME="sec8"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 20.3.6</I></P>
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<BR>
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