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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_asio.reference.async_connect.overload4"></a><a class="link" href="overload4.html" title="async_connect (4 of 4 overloads)">async_connect |
| (4 of 4 overloads)</a> |
| </h4></div></div></div> |
| <p> |
| Asynchronously establishes a socket connection by trying each endpoint |
| in a sequence. |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> |
| <span class="keyword">typename</span> <a class="link" href="../Protocol.html" title="Protocol requirements">Protocol</a><span class="special">,</span> |
| <span class="keyword">typename</span> <a class="link" href="../SocketService.html" title="Socket service requirements">SocketService</a><span class="special">,</span> |
| <span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> |
| <span class="keyword">typename</span> <span class="identifier">ConnectCondition</span><span class="special">,</span> |
| <span class="keyword">typename</span> <a class="link" href="../ComposedConnectHandler.html" title="Composed connect handler requirements">ComposedConnectHandler</a><span class="special">></span> |
| <span class="keyword">void</span> <span class="identifier">async_connect</span><span class="special">(</span> |
| <span class="identifier">basic_socket</span><span class="special"><</span> <span class="identifier">Protocol</span><span class="special">,</span> <span class="identifier">SocketService</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span> |
| <span class="identifier">Iterator</span> <span class="identifier">begin</span><span class="special">,</span> |
| <span class="identifier">Iterator</span> <span class="identifier">end</span><span class="special">,</span> |
| <span class="identifier">ConnectCondition</span> <span class="identifier">connect_condition</span><span class="special">,</span> |
| <span class="identifier">ComposedConnectHandler</span> <span class="identifier">handler</span><span class="special">);</span> |
| </pre> |
| <p> |
| This function attempts to connect a socket to one of a sequence of endpoints. |
| It does this by repeated calls to the socket's <code class="computeroutput"><span class="identifier">async_connect</span></code> |
| member function, once for each endpoint in the sequence, until a connection |
| is successfully established. |
| </p> |
| <a name="boost_asio.reference.async_connect.overload4.parameters"></a><h6> |
| <a name="boost_asio.reference.async_connect.overload4.parameters-heading"></a> |
| <a class="link" href="overload4.html#boost_asio.reference.async_connect.overload4.parameters">Parameters</a> |
| </h6> |
| <div class="variablelist"> |
| <p class="title"><b></b></p> |
| <dl> |
| <dt><span class="term">s</span></dt> |
| <dd><p> |
| The socket to be connected. If the socket is already open, it will |
| be closed. |
| </p></dd> |
| <dt><span class="term">begin</span></dt> |
| <dd><p> |
| An iterator pointing to the start of a sequence of endpoints. |
| </p></dd> |
| <dt><span class="term">end</span></dt> |
| <dd><p> |
| An iterator pointing to the end of a sequence of endpoints. |
| </p></dd> |
| <dt><span class="term">connect_condition</span></dt> |
| <dd> |
| <p> |
| A function object that is called prior to each connection attempt. |
| The signature of the function object must be: |
| </p> |
| <pre class="programlisting"><span class="identifier">Iterator</span> <span class="identifier">connect_condition</span><span class="special">(</span> |
| <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">&</span> <span class="identifier">ec</span><span class="special">,</span> |
| <span class="identifier">Iterator</span> <span class="identifier">next</span><span class="special">);</span> |
| </pre> |
| <p> |
| The <code class="computeroutput"><span class="identifier">ec</span></code> parameter |
| contains the result from the most recent connect operation. Before |
| the first connection attempt, <code class="computeroutput"><span class="identifier">ec</span></code> |
| is always set to indicate success. The <code class="computeroutput"><span class="identifier">next</span></code> |
| parameter is an iterator pointing to the next endpoint to be tried. |
| The function object should return the next iterator, but is permitted |
| to return a different iterator so that endpoints may be skipped. |
| The implementation guarantees that the function object will never |
| be called with the end iterator. |
| </p> |
| </dd> |
| <dt><span class="term">handler</span></dt> |
| <dd> |
| <p> |
| The handler to be called when the connect operation completes. Copies |
| will be made of the handler as required. The function signature of |
| the handler must be: |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span> |
| <span class="comment">// Result of operation. if the sequence is empty, set to</span> |
| <span class="comment">// boost::asio::error::not_found. Otherwise, contains the</span> |
| <span class="comment">// error from the last connection attempt.</span> |
| <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">&</span> <span class="identifier">error</span><span class="special">,</span> |
| |
| <span class="comment">// On success, an iterator denoting the successfully</span> |
| <span class="comment">// connected endpoint. Otherwise, the end iterator.</span> |
| <span class="identifier">Iterator</span> <span class="identifier">iterator</span> |
| <span class="special">);</span> |
| </pre> |
| <p> |
| Regardless of whether the asynchronous operation completes immediately |
| or not, the handler will not be invoked from within this function. |
| Invocation of the handler will be performed in a manner equivalent |
| to using <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">post</span><span class="special">()</span></code>. |
| </p> |
| </dd> |
| </dl> |
| </div> |
| <a name="boost_asio.reference.async_connect.overload4.example"></a><h6> |
| <a name="boost_asio.reference.async_connect.overload4.example-heading"></a> |
| <a class="link" href="overload4.html#boost_asio.reference.async_connect.overload4.example">Example</a> |
| </h6> |
| <p> |
| The following connect condition function object can be used to output information |
| about the individual connection attempts: |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_connect_condition</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">></span> |
| <span class="identifier">Iterator</span> <span class="keyword">operator</span><span class="special">()(</span> |
| <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">&</span> <span class="identifier">ec</span><span class="special">,</span> |
| <span class="identifier">Iterator</span> <span class="identifier">next</span><span class="special">)</span> |
| <span class="special">{</span> |
| <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"><<</span> <span class="string">"Error: "</span> <span class="special"><<</span> <span class="identifier">ec</span><span class="special">.</span><span class="identifier">message</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Trying: "</span> <span class="special"><<</span> <span class="identifier">next</span><span class="special">-></span><span class="identifier">endpoint</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="identifier">next</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| 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> |
| function as follows: |
| </p> |
| <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> |
| <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> |
| <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> |
| |
| <span class="comment">// ...</span> |
| |
| <span class="identifier">r</span><span class="special">.</span><span class="identifier">async_resolve</span><span class="special">(</span><span class="identifier">q</span><span class="special">,</span> <span class="identifier">resolve_handler</span><span class="special">);</span> |
| |
| <span class="comment">// ...</span> |
| |
| <span class="keyword">void</span> <span class="identifier">resolve_handler</span><span class="special">(</span> |
| <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">&</span> <span class="identifier">ec</span><span class="special">,</span> |
| <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="special">{</span> |
| <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">ec</span><span class="special">)</span> |
| <span class="special">{</span> |
| <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">end</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">async_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">connect_handler</span><span class="special">);</span> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| |
| <span class="comment">// ...</span> |
| |
| <span class="keyword">void</span> <span class="identifier">connect_handler</span><span class="special">(</span> |
| <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">&</span> <span class="identifier">ec</span><span class="special">,</span> |
| <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="special">{</span> |
| <span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="comment">// An error occurred.</span> |
| <span class="special">}</span> |
| <span class="keyword">else</span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Connected to: "</span> <span class="special"><<</span> <span class="identifier">i</span><span class="special">-></span><span class="identifier">endpoint</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| </pre> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2003-2011 Christopher |
| M. Kohlhoff<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>) |
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