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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.connect.overload8"></a><a class="link" href="overload8.html" title="connect (8 of 8 overloads)">connect (8
  28         of 8 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Establishes a socket connection by trying each endpoint in a sequence.
  32         </p>
  33 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
  34     <span class="keyword">typename</span> <a class="link" href="../Protocol.html" title="Protocol requirements">Protocol</a><span class="special">,</span>
  35     <span class="keyword">typename</span> <a class="link" href="../SocketService.html" title="Socket service requirements">SocketService</a><span class="special">,</span>
  36     <span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span>
  37     <span class="keyword">typename</span> <span class="identifier">ConnectCondition</span><span class="special">&gt;</span>
  38 <span class="identifier">Iterator</span> <span class="identifier">connect</span><span class="special">(</span>
  39     <span class="identifier">basic_socket</span><span class="special">&lt;</span> <span class="identifier">Protocol</span><span class="special">,</span> <span class="identifier">SocketService</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">s</span><span class="special">,</span>
  40     <span class="identifier">Iterator</span> <span class="identifier">begin</span><span class="special">,</span>
  41     <span class="identifier">Iterator</span> <span class="identifier">end</span><span class="special">,</span>
  42     <span class="identifier">ConnectCondition</span> <span class="identifier">connect_condition</span><span class="special">,</span>
  43     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="special">&amp;</span> <span class="identifier">ec</span><span class="special">);</span>
  44 </pre>
  45 <p>
  46           This function attempts to connect a socket to one of a sequence of endpoints.
  47           It does this by repeated calls to the socket's <code class="computeroutput"><span class="identifier">connect</span></code>
  48           member function, once for each endpoint in the sequence, until a connection
  49           is successfully established.
  50         </p>
  51 <h6>
  52 <a name="boost_asio.reference.connect.overload8.h0"></a>
  53           <span class="phrase"><a name="boost_asio.reference.connect.overload8.parameters"></a></span><a class="link" href="overload8.html#boost_asio.reference.connect.overload8.parameters">Parameters</a>
  54         </h6>
  55 <div class="variablelist">
  56 <p class="title"><b></b></p>
  57 <dl class="variablelist">
  58 <dt><span class="term">s</span></dt>
  59 <dd><p>
  60                 The socket to be connected. If the socket is already open, it will
  61                 be closed.
  62               </p></dd>
  63 <dt><span class="term">begin</span></dt>
  64 <dd><p>
  65                 An iterator pointing to the start of a sequence of endpoints.
  66               </p></dd>
  67 <dt><span class="term">end</span></dt>
  68 <dd><p>
  69                 An iterator pointing to the end of a sequence of endpoints.
  70               </p></dd>
  71 <dt><span class="term">connect_condition</span></dt>
  72 <dd>
  73 <p>
  74                 A function object that is called prior to each connection attempt.
  75                 The signature of the function object must be:
  76 </p>
  77 <pre class="programlisting"><span class="identifier">Iterator</span> <span class="identifier">connect_condition</span><span class="special">(</span>
  78     <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">ec</span><span class="special">,</span>
  79     <span class="identifier">Iterator</span> <span class="identifier">next</span><span class="special">);</span>
  80 </pre>
  81 <p>
  82                 The <code class="computeroutput"><span class="identifier">ec</span></code> parameter
  83                 contains the result from the most recent connect operation. Before
  84                 the first connection attempt, <code class="computeroutput"><span class="identifier">ec</span></code>
  85                 is always set to indicate success. The <code class="computeroutput"><span class="identifier">next</span></code>
  86                 parameter is an iterator pointing to the next endpoint to be tried.
  87                 The function object should return the next iterator, but is permitted
  88                 to return a different iterator so that endpoints may be skipped.
  89                 The implementation guarantees that the function object will never
  90                 be called with the end iterator.
  91               </p>
  92 </dd>
  93 <dt><span class="term">ec</span></dt>
  94 <dd><p>
  95                 Set to indicate what error occurred, if any. If the sequence is empty,
  96                 set to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">not_found</span></code>. Otherwise, contains
  97                 the error from the last connection attempt.
  98               </p></dd>
  99 </dl>
 100 </div>
 101 <h6>
 102 <a name="boost_asio.reference.connect.overload8.h1"></a>
 103           <span class="phrase"><a name="boost_asio.reference.connect.overload8.return_value"></a></span><a class="link" href="overload8.html#boost_asio.reference.connect.overload8.return_value">Return Value</a>
 104         </h6>
 105 <p>
 106           On success, an iterator denoting the successfully connected endpoint. Otherwise,
 107           the end iterator.
 108         </p>
 109 <h6>
 110 <a name="boost_asio.reference.connect.overload8.h2"></a>
 111           <span class="phrase"><a name="boost_asio.reference.connect.overload8.example"></a></span><a class="link" href="overload8.html#boost_asio.reference.connect.overload8.example">Example</a>
 112         </h6>
 113 <p>
 114           The following connect condition function object can be used to output information
 115           about the individual connection attempts:
 116         </p>
 117 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_connect_condition</span>
 118 <span class="special">{</span>
 119   <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
 120   <span class="identifier">Iterator</span> <span class="keyword">operator</span><span class="special">()(</span>
 121       <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">ec</span><span class="special">,</span>
 122       <span class="identifier">Iterator</span> <span class="identifier">next</span><span class="special">)</span>
 123   <span class="special">{</span>
 124     <span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Error: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">ec</span><span class="special">.</span><span class="identifier">message</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 125     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Trying: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">next</span><span class="special">-&gt;</span><span class="identifier">endpoint</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 126     <span class="keyword">return</span> <span class="identifier">next</span><span class="special">;</span>
 127   <span class="special">}</span>
 128 <span class="special">};</span>
 129 </pre>
 130 <p>
 131           It would be used with the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span></code>
 132           function as follows:
 133         </p>
 134 <pre class="programlisting"><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span> <span class="identifier">r</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span>
 135 <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">query</span> <span class="identifier">q</span><span class="special">(</span><span class="string">"host"</span><span class="special">,</span> <span class="string">"service"</span><span class="special">);</span>
 136 <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">resolve</span><span class="special">(</span><span class="identifier">q</span><span class="special">),</span> <span class="identifier">end</span><span class="special">;</span>
 137 <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span>
 138 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">;</span>
 139 <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">i</span><span class="special">,</span> <span class="identifier">end</span><span class="special">,</span> <span class="identifier">my_connect_condition</span><span class="special">(),</span> <span class="identifier">ec</span><span class="special">);</span>
 140 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span>
 141 <span class="special">{</span>
 142   <span class="comment">// An error occurred.</span>
 143 <span class="special">}</span>
 144 <span class="keyword">else</span>
 145 <span class="special">{</span>
 146   <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Connected to: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">i</span><span class="special">-&gt;</span><span class="identifier">endpoint</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 147 <span class="special">}</span>
 148 </pre>
 149 </div>
 150 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 151 <td align="left"></td>
 152 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2017 Christopher M. Kohlhoff<p>
 153         Distributed under the Boost Software License, Version 1.0. (See accompanying
 154         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 155       </p>
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