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<title>async_connect (6 of 6 overloads)</title>
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<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.async_connect.overload6"></a><a class="link" href="overload6.html" title="async_connect (6 of 6 overloads)">async_connect
(6 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">template<
typename <a class="link" href="../Protocol.html" title="Protocol requirements">Protocol</a>,
typename <a class="link" href="../Executor1.html" title="Executor requirements">Executor</a>,
typename Iterator,
typename <a class="link" href="../ConnectCondition.html" title="Connect condition requirements">ConnectCondition</a>,
typename <a class="link" href="../IteratorConnectHandler.html" title="Iterator connect handler requirements">IteratorConnectHandler</a> = <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>>
<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> async_connect(
basic_socket< Protocol, Executor > & s,
Iterator begin,
Iterator end,
ConnectCondition connect_condition,
IteratorConnectHandler && handler = <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>);
</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">async_connect</code>
member function, once for each endpoint in the sequence, until a connection
is successfully established.
</p>
<h6>
<a name="asio.reference.async_connect.overload6.h0"></a>
<span><a name="asio.reference.async_connect.overload6.parameters"></a></span><a class="link" href="overload6.html#asio.reference.async_connect.overload6.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">bool connect_condition(
const asio::error_code& ec,
const typename Protocol::endpoint& next);
</pre>
<p>
The <code class="computeroutput">ec</code> parameter contains the result from the most recent
connect operation. Before the first connection attempt, <code class="computeroutput">ec</code>
is always set to indicate success. The <code class="computeroutput">next</code> parameter
is the next endpoint to be tried. The function object should return
true if the next endpoint should be tried, and false if it should
be skipped.
</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">void handler(
// Result of operation. if the sequence is empty, set to
// asio::error::not_found. Otherwise, contains the
// error from the last connection attempt.
const asio::error_code& error,
// On success, an iterator denoting the successfully
// connected endpoint. Otherwise, the end iterator.
Iterator iterator
);
</pre>
<p>
Regardless of whether the asynchronous operation completes immediately
or not, the 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">post</code></a>.
</p>
</dd>
</dl>
</div>
<h6>
<a name="asio.reference.async_connect.overload6.h1"></a>
<span><a name="asio.reference.async_connect.overload6.example"></a></span><a class="link" href="overload6.html#asio.reference.async_connect.overload6.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">struct my_connect_condition
{
bool operator()(
const asio::error_code& ec,
const::tcp::endpoint& next)
{
if (ec) std::cout << "Error: " << ec.message() << std::endl;
std::cout << "Trying: " << next << std::endl;
return true;
}
};
</pre>
<p>
It would be used with the <code class="computeroutput">asio::connect</code> function as follows:
</p>
<pre class="programlisting">tcp::resolver r(my_context);
tcp::resolver::query q("host", "service");
tcp::socket s(my_context);
// ...
r.async_resolve(q, resolve_handler);
// ...
void resolve_handler(
const asio::error_code& ec,
tcp::resolver::iterator i)
{
if (!ec)
{
tcp::resolver::iterator end;
asio::async_connect(s, i, end,
my_connect_condition(),
connect_handler);
}
}
// ...
void connect_handler(
const asio::error_code& ec,
tcp::resolver::iterator i)
{
if (ec)
{
// An error occurred.
}
else
{
std::cout << "Connected to: " << i->endpoint() << std::endl;
}
}
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2020 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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