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<title>async_connect (1 of 6 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.async_connect.overload1"></a><a class="link" href="overload1.html" title="async_connect (1 of 6 overloads)">async_connect
(1 of 6 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">&lt;</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="../Executor1.html" title="Executor requirements">Executor</a><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../EndpointSequence.html" title="Endpoint sequence requirements">EndpointSequence</a><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../RangeConnectToken.html" title="Range connect token requirements">RangeConnectToken</a> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">&gt;</span>
<a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> <span class="identifier">async_connect</span><span class="special">(</span>
<span class="identifier">basic_socket</span><span class="special">&lt;</span> <span class="identifier">Protocol</span><span class="special">,</span> <span class="identifier">Executor</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">s</span><span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">EndpointSequence</span> <span class="special">&amp;</span> <span class="identifier">endpoints</span><span class="special">,</span>
<span class="identifier">RangeConnectToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">constraint</span><span class="special">&lt;</span> <span class="identifier">is_endpoint_sequence</span><span class="special">&lt;</span> <span class="identifier">EndpointSequence</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;::</span><span class="identifier">type</span> <span class="special">=</span> <span class="number">0</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. It is an initiating function for an <a class="link" href="../../overview/model/async_ops.html" title="Asynchronous Operations">asynchronous operation</a>,
and always returns immediately.
</p>
<h6>
<a name="asio.reference.async_connect.overload1.h0"></a>
<span><a name="asio.reference.async_connect.overload1.parameters"></a></span><a class="link" href="overload1.html#asio.reference.async_connect.overload1.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">endpoints</span></dt>
<dd><p>
A sequence of endpoints.
</p></dd>
<dt><span class="term">token</span></dt>
<dd>
<p>
The <a class="link" href="../../overview/model/completion_tokens.html" title="Completion Tokens">completion
token</a> that will be used to produce a completion handler, which
will be called when the connect completes. Potential completion tokens
include <a class="link" href="../use_future.html" title="use_future"><code class="computeroutput"><span class="identifier">use_future</span></code></a>,
<a class="link" href="../use_awaitable.html" title="use_awaitable"><code class="computeroutput"><span class="identifier">use_awaitable</span></code></a>,
<a class="link" href="../yield_context.html" title="yield_context"><code class="computeroutput"><span class="identifier">yield_context</span></code></a>,
or a function object with the correct completion signature. The function
signature of the completion 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">// 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">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">error</span><span class="special">,</span>
<span class="comment">// On success, the successfully connected endpoint.</span>
<span class="comment">// Otherwise, a default-constructed endpoint.</span>
<span class="keyword">const</span> <span class="keyword">typename</span> <span class="identifier">Protocol</span><span class="special">::</span><span class="identifier">endpoint</span><span class="special">&amp;</span> <span class="identifier">endpoint</span>
<span class="special">);</span>
</pre>
<p>
Regardless of whether the asynchronous operation completes immediately
or not, the completion handler will not be invoked from within this
function. On immediate completion, invocation of the handler will
be performed in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput"><span class="identifier">post</span></code></a>.
</p>
</dd>
</dl>
</div>
<h6>
<a name="asio.reference.async_connect.overload1.h1"></a>
<span><a name="asio.reference.async_connect.overload1.completion_signature"></a></span><a class="link" href="overload1.html#asio.reference.async_connect.overload1.completion_signature">Completion
Signature</a>
</h6>
<pre class="programlisting"><span class="keyword">void</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Protocol</span><span class="special">::</span><span class="identifier">endpoint</span><span class="special">)</span>
</pre>
<h6>
<a name="asio.reference.async_connect.overload1.h2"></a>
<span><a name="asio.reference.async_connect.overload1.example"></a></span><a class="link" href="overload1.html#asio.reference.async_connect.overload1.example">Example</a>
</h6>
<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">my_context</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">my_context</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">asio</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>
<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">results_type</span> <span class="identifier">results</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">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">results</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">asio</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>
<span class="keyword">const</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">endpoint</span><span class="special">&amp;</span> <span class="identifier">endpoint</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// ...</span>
<span class="special">}</span>
</pre>
<h6>
<a name="asio.reference.async_connect.overload1.h3"></a>
<span><a name="asio.reference.async_connect.overload1.per_operation_cancellation"></a></span><a class="link" href="overload1.html#asio.reference.async_connect.overload1.per_operation_cancellation">Per-Operation
Cancellation</a>
</h6>
<p>
This asynchronous operation supports cancellation for the following <a class="link" href="../cancellation_type.html" title="cancellation_type"><code class="computeroutput"><span class="identifier">cancellation_type</span></code></a>
values:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
<code class="computeroutput"><span class="identifier">cancellation_type</span><span class="special">::</span><span class="identifier">terminal</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">cancellation_type</span><span class="special">::</span><span class="identifier">partial</span></code>
</li>
</ul></div>
<p>
if they are also supported by the socket's <code class="computeroutput"><span class="identifier">async_connect</span></code>
operation.
</p>
</div>
<div class="copyright-footer">Copyright © 2003-2023 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>)
</p>
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