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<title>async_write (6 of 8 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.async_write.overload6"></a><a class="link" href="overload6.html" title="async_write (6 of 8 overloads)">async_write (6
of 8 overloads)</a>
</h4></div></div></div>
<p>
Start an asynchronous operation to write a certain amount of data to a
stream.
</p>
<pre class="programlisting">template<
typename <a class="link" href="../AsyncWriteStream.html" title="Buffer-oriented asynchronous write stream requirements">AsyncWriteStream</a>,
typename Allocator,
typename <a class="link" href="../CompletionCondition.html" title="Completion condition requirements">CompletionCondition</a>,
typename <a class="link" href="../WriteHandler.html" title="Write handler requirements">WriteHandler</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_write(
AsyncWriteStream & s,
basic_streambuf< Allocator > & b,
CompletionCondition completion_condition,
WriteHandler && handler);
</pre>
<p>
This function is used to asynchronously write a certain number of bytes
of data to a stream. The function call always returns immediately. The
asynchronous operation will continue until one of the following conditions
is true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
All of the data in the supplied <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a>
has been written.
</li>
<li class="listitem">
The completion_condition function object returns 0.
</li>
</ul></div>
<p>
This operation is implemented in terms of zero or more calls to the stream's
async_write_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
The program must ensure that the stream performs no other write operations
(such as async_write, the stream's async_write_some function, or any other
composed operations that perform writes) until this operation completes.
</p>
<h6>
<a name="asio.reference.async_write.overload6.h0"></a>
<span><a name="asio.reference.async_write.overload6.parameters"></a></span><a class="link" href="overload6.html#asio.reference.async_write.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 stream to which the data is to be written. The type must support
the AsyncWriteStream concept.
</p></dd>
<dt><span class="term">b</span></dt>
<dd><p>
A <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a>
object from which data will be written. Ownership of the streambuf
is retained by the caller, which must guarantee that it remains valid
until the handler is called.
</p></dd>
<dt><span class="term">completion_condition</span></dt>
<dd>
<p>
The function object to be called to determine whether the write operation
is complete. The signature of the function object must be:
</p>
<pre class="programlisting">std::size_t completion_condition(
// Result of latest async_write_some operation.
const asio::error_code& error,
// Number of bytes transferred so far.
std::size_t bytes_transferred
);
</pre>
<p>
A return value of 0 indicates that the write operation is complete.
A non-zero return value indicates the maximum number of bytes to
be written on the next call to the stream's async_write_some function.
</p>
</dd>
<dt><span class="term">handler</span></dt>
<dd>
<p>
The handler to be called when the write 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(
const asio::error_code& error, // Result of operation.
std::size_t bytes_transferred // Number of bytes written from the
// buffers. If an error occurred,
// this will be less than the sum
// of the buffer sizes.
);
</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>
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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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