<!--
    Licensed to the Apache Software  Foundation (ASF) under one or more
    contributor  license agreements.  See  the NOTICE  file distributed
    with  this  work  for  additional information  regarding  copyright
    ownership.   The ASF  licenses this  file to  you under  the Apache
    License, Version  2.0 (the  License); you may  not use  this file
    except in  compliance with the License.   You may obtain  a copy of
    the License at

    http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the  License is distributed on an  "AS IS" BASIS,
    WITHOUT  WARRANTIES OR CONDITIONS  OF ANY  KIND, either  express or
    implied.   See  the License  for  the  specific language  governing
    permissions and limitations under the License.

    Copyright 1999-2007 Rogue Wave Software, Inc.
-->

<HTML>
<HEAD>
<TITLE>bind1st(), bind2nd(), binder1st, binder2nd</TITLE>
<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
<BODY BGCOLOR=#FFFFFF>
<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>
<H2>bind1st(), bind2nd(), binder1st, binder2nd</H2>
<P><B>Library:</B>&nbsp;&nbsp;<A HREF="2-4.html">General utilities</A></P>

<PRE><HR><B><I>Function</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Interface</A></LI>
<LI><A HREF="#sec6">Example</A></LI>
<LI><A HREF="#sec7">See Also</A></LI>
<LI><A HREF="#sec8">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
No Entries
<A NAME="sec2"><H3>Summary</H3></A>
<P>Templatized utilities to bind values to function objects</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;functional&gt;

namespace std {
  template &lt;class Operation&gt;
  class binder1st;
  
  template &lt;class Operation, class T&gt;
  binder1st&lt;Operation&gt; bind1st(const Operation&amp;, const T&amp;);

  template &lt;class Operation&gt;
  class binder2nd ;

  template &lt;class Operation, class T&gt;
  binder2nd&lt;Operation&gt; bind2nd(const Operation&amp;, const T&amp;);
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<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>
<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>
<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>

<UL><PRE>
vector&lt;int&gt; v;<br>int littleNums;<br>
count_if(v.begin, v.end, bind1st(greater&lt;int&gt;(),7),
         littleNums)
</PRE></UL>
<P>This function adds one to <SAMP>littleNums</SAMP> each time the element is greater than&nbsp;7.</P>
<A NAME="sec5"><H3>Interface</H3></A>

<UL><PRE>namespace std {

  // Class binder1st 
  template &lt;class Operation&gt;
  class binder1st
     : public unary_function&lt;typename 
                             Operation::second_argument_type,
                             typename Operation::result_type&gt;
  {
  public:

     binder1st(const Operation&amp;,
               const typename Operation::first_argument_type&amp;);
     
     typename Operation::result_type 
     operator() (const typename
                 Operation::second_argument_type&amp;) const;
  };

  // Class binder2nd 
  template &lt;class Operation&gt;
  class binder2nd
     : public unary_function&lt;typename 
                         Operation::first_argument_type, 
                         typename Operation::result_type&gt;
  {
  public:

     binder2nd(const Operation&amp;,
               const typename Operation::second_argument_type&amp;);
     typename Operation::result_type 
     operator()(const typename 
                Operation::first_argument_type&amp;) const;
  };

  // Creator bind1st
  template &lt;class Operation, class T&gt;
  binder1st&lt;Operation&gt; bind1st(const Operation&amp;, const T&amp;);

  // Creator bind2nd 
  template&lt;class Operation, class T&gt;
  binder2nd &lt;Operation&gt; bind2nd(const Operation&amp;, const T&amp;);
}
</PRE></UL>
<A NAME="sec6"><H3>Example</H3></A>

<UL><PRE>//
// binders.cpp
//

#include &lt;algorithm&gt;   // for find_if
#include &lt;functional&gt;  // for equal_to, bind1st, bind2nd
#include &lt;iostream&gt;    // for cout
#include &lt;iterator&gt;    // for ostream_iterator
#include &lt;vector&gt;      // for vector


int main ()
{
    typedef std::vector&lt;int&gt;                  Vector;
    typedef std::equal_to&lt;Vector::value_type&gt; EqualTo;

    const Vector::value_type arr [] = { 1, 2, 3, 4, 5 };

    // Initialize a vector with the array elements.
    const Vector v1 (arr, arr + sizeof arr / sizeof *arr);

    // Value to look for.
    const Vector::value_type x (3);

    // Create an 'equal to 3' unary predicate by binding the value
    // 3 to the EqualTo binary predicate.
    const std::binder1st&lt;EqualTo&gt; equal_to_3 =
        std::bind1st (EqualTo (), x);

    // Now use this new predicate in a call to find_if.
    const Vector::const_iterator it1 =
        std::find_if (v1.begin (), v1.end (), equal_to_3);

    // Even better, construct the new predicate on the fly.
    const Vector::const_iterator it2 =
        std::find_if (v1.begin (), v1.end (), std::bind1st (EqualTo (), x));

    // And now the same thing using bind2nd.
    // Same result since EqualTo is commutative.
    const Vector::const_iterator it3 =
        std::find_if (v1.begin (), v1.end (), std::bind2nd (EqualTo (), x));

    // Use the same predicate to count the number of elements
    // equal to 3.
    const Vector::size_type n =
        std::count_if (v1.begin (), v1.end (), std::bind2nd (EqualTo (), x));

    // Output results.
    std::ostream_iterator&lt;Vector::value_type&gt; out (std::cout, " ");

    std::cout &lt;&lt; "The vector { ";
    std::copy (v1.begin (), v1.end (), out);

    std::cout &lt;&lt; "} contains " &lt;&lt; n &lt;&lt; " element equal to "
              &lt;&lt; x &lt;&lt;  " at offset " &lt;&lt;
              it1 - v1.begin () &lt;&lt; ".\n";
    
    // Exit with status of 0 on success, 1 on failure.
    const bool success = 1 == n && it1 == it2 && it1 == it2 && *it1 == x;

    return success ? 0 : 1;
}

Program Output:
The vector { 1 2 3 4 5 } contains 1 element equal to 3 at offset 2.
</PRE></UL>
<UL><PRE></PRE></UL>
<A NAME="sec7"><H3>See Also</H3></A>
<P><A HREF="functionobjects.html">Function Objects</A></P>
<A NAME="sec8"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 20.3.6</I></P>

<BR>
<HR>
<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=20 HEIGHT=21 ALT="Next file" BORDER=O></A>

<!-- Google Analytics tracking code -->
<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
</script>
<script type="text/javascript">
    _uacct = "UA-1775151-1";
    urchinTracker();
</script>
<!-- end of Google Analytics tracking code -->

</BODY>
</HTML>