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  26 <div class="titlepage"><div><div><h6 class="title">
  27 <a name="beast.ref.boost__beast__basic_stream.async_connect.overload3"></a><a class="link" href="overload3.html" title="basic_stream::async_connect (3 of 5 overloads)">basic_stream::async_connect
  28           (3 of 5 overloads)</a>
  29 </h6></div></div></div>
  30 <p>
  31             Establishes a connection by trying each endpoint in a sequence asynchronously.
  32           </p>
  33 <h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h0"></a>
  34             <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.synopsis"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.synopsis">Synopsis</a>
  35           </h7><pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
  36     <span class="keyword">class</span> <a href="../../../../../../../../doc/html/boost_asio/reference/EndpointSequence.html" target="_top"><span class="emphasis"><em>EndpointSequence</em></span></a><span class="special">,</span>
  37     <span class="keyword">class</span> <a href="../../../../../../../../doc/html/boost_asio/reference/ConnectCondition.html" target="_top"><span class="emphasis"><em>ConnectCondition</em></span></a><span class="special">,</span>
  38     <span class="keyword">class</span> <a href="../../../../../../../../doc/html/boost_asio/reference/RangeConnectHandler.html" target="_top"><span class="emphasis"><em>RangeConnectHandler</em></span></a> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">default_completion_token_t</span><span class="special">&lt;</span><span class="identifier">executor_type</span><span class="special">&gt;&gt;</span>
  39 <a href="../../../../../../../../doc/html/boost_asio/reference/asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type" target="_top"><span class="emphasis"><em>DEDUCED</em></span></a>
  40 <span class="identifier">async_connect</span><span class="special">(</span>
  41     <span class="identifier">EndpointSequence</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">endpoints</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">RangeConnectHandler</span><span class="special">&amp;&amp;</span> <span class="identifier">handler</span> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="identifier">executor_type</span> <span class="special">&gt;{});</span>
  44 </pre>
  45 <h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h1"></a>
  46             <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.description"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.description">Description</a>
  47           </h7><p>
  48             This function attempts to connect the stream to one of a sequence of
  49             endpoints by trying each endpoint until a connection is successfully
  50             established. The underlying socket is automatically opened if needed.
  51             An automatically opened socket is not returned to the closed state upon
  52             failure. The algorithm, known as a <span class="emphasis"><em>composed asynchronous operation</em></span>,
  53             is implemented in terms of calls to the underlying socket's <code class="computeroutput"><span class="identifier">async_connect</span></code> function. If the timeout
  54             timer expires while the operation is outstanding, the current connection
  55             attempt will be canceled and the completion handler will be invoked with
  56             the error <a class="link" href="../../boost__beast__error.html" title="error"><code class="computeroutput"><span class="identifier">timeout</span></code></a>.
  57           </p>
  58 <h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h2"></a>
  59             <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.parameters"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.parameters">Parameters</a>
  60           </h7><div class="informaltable"><table class="table">
  61 <colgroup>
  62 <col>
  63 <col>
  64 </colgroup>
  65 <thead><tr>
  66 <th>
  67                     <p>
  68                       Name
  69                     </p>
  70                   </th>
  71 <th>
  72                     <p>
  73                       Description
  74                     </p>
  75                   </th>
  76 </tr></thead>
  77 <tbody>
  78 <tr>
  79 <td>
  80                     <p>
  81                       <code class="computeroutput"><span class="identifier">endpoints</span></code>
  82                     </p>
  83                   </td>
  84 <td>
  85                     <p>
  86                       A sequence of endpoints. This this object must meet the requirements
  87                       of <span class="emphasis"><em>EndpointSequence</em></span>.
  88                     </p>
  89                   </td>
  90 </tr>
  91 <tr>
  92 <td>
  93                     <p>
  94                       <code class="computeroutput"><span class="identifier">connect_condition</span></code>
  95                     </p>
  96                   </td>
  97 <td>
  98                     <p>
  99                       A function object that is called prior to each connection attempt.
 100                       The signature of the function object must be:
 101                     </p>
 102 <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">bool</span> <span class="identifier">connect_condition</span><span class="special">(</span>
 103     <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">ec</span><span class="special">,</span>
 104     <span class="keyword">typename</span> <span class="identifier">Protocol</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">next</span><span class="special">);</span>
 105 </pre>
 106                     <p>
 107                       The <code class="computeroutput"><span class="identifier">ec</span></code> parameter
 108                       contains the result from the most recent connect operation.
 109                       Before the first connection attempt, <code class="computeroutput"><span class="identifier">ec</span></code>
 110                       is always set to indicate success. The <code class="computeroutput"><span class="identifier">next</span></code>
 111                       parameter is the next endpoint to be tried. The function object
 112                       should return true if the next endpoint should be tried, and
 113                       false if it should be skipped.
 114                     </p>
 115                   </td>
 116 </tr>
 117 <tr>
 118 <td>
 119                     <p>
 120                       <code class="computeroutput"><span class="identifier">handler</span></code>
 121                     </p>
 122                   </td>
 123 <td>
 124                     <p>
 125                       The completion handler to invoke when the operation completes.
 126                       The implementation takes ownership of the handler by performing
 127                       a decay-copy. The equivalent function signature of the handler
 128                       must be:
 129                     </p>
 130 <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
 131     <span class="comment">// Result of operation. if the sequence is empty, set to</span>
 132     <span class="comment">// net::error::not_found. Otherwise, contains the</span>
 133     <span class="comment">// error from the last connection attempt.</span>
 134     <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">error</span><span class="special">,</span>
 135
 136     <span class="comment">// On success, the successfully connected endpoint.</span>
 137     <span class="comment">// Otherwise, a default-constructed endpoint.</span>
 138     <span class="keyword">typename</span> <span class="identifier">Protocol</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">endpoint</span>
 139 <span class="special">);</span>
 140 </pre>
 141                     <p>
 142                       Regardless of whether the asynchronous operation completes
 143                       immediately or not, the handler will not be invoked from within
 144                       this function. Invocation of the handler will be performed
 145                       in a manner equivalent to using <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span></code>.
 146                     </p>
 147                   </td>
 148 </tr>
 149 </tbody>
 150 </table></div>
 151 <h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h3"></a>
 152             <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.example"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.example">Example</a>
 153           </h7><p>
 154             The following connect condition function object can be used to output
 155             information about the individual connection attempts:
 156           </p>
 157 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_connect_condition</span>
 158 <span class="special">{</span>
 159     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span>
 160         <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">ec</span><span class="special">,</span>
 161         <span class="identifier">net</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">next</span><span class="special">)</span>
 162     <span class="special">{</span>
 163         <span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span>
 164             <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>
 165         <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">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 166         <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span>
 167     <span class="special">}</span>
 168 <span class="special">};</span>
 169 </pre>
 170 </div>
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