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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"><span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <a class="link" href="../AsyncWriteStream.html" title="Buffer-oriented asynchronous write stream requirements">AsyncWriteStream</a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../CompletionCondition.html" title="Completion condition requirements">CompletionCondition</a><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../WriteToken.html" title="Write token requirements">WriteToken</a><span class="special">></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_write</span><span class="special">(</span>
<span class="identifier">AsyncWriteStream</span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span>
<span class="identifier">basic_streambuf</span><span class="special"><</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">b</span><span class="special">,</span>
<span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">,</span>
<span class="identifier">WriteToken</span> <span class="special">&&</span> <span class="identifier">token</span><span class="special">);</span>
</pre>
<p>
This function is used to asynchronously write a certain number of bytes
of data to a stream. 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. 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"><span class="identifier">basic_streambuf</span></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"><span class="identifier">basic_streambuf</span></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 completion 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"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">completion_condition</span><span class="special">(</span>
<span class="comment">// Result of latest async_write_some operation.</span>
<span class="keyword">const</span> <span class="identifier">asio</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">// Number of bytes transferred so far.</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
<span class="special">);</span>
</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">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 write 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.</span>
<span class="keyword">const</span> <span class="identifier">asio</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">// Number of bytes written from the buffers. If an error</span>
<span class="comment">// occurred, this will be less than the sum of the buffer sizes.</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</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_write.overload6.h1"></a>
<span><a name="asio.reference.async_write.overload6.completion_signature"></a></span><a class="link" href="overload6.html#asio.reference.async_write.overload6.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="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">)</span>
</pre>
<h6>
<a name="asio.reference.async_write.overload6.h2"></a>
<span><a name="asio.reference.async_write.overload6.per_operation_cancellation"></a></span><a class="link" href="overload6.html#asio.reference.async_write.overload6.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 <code class="computeroutput"><span class="identifier">AsyncWriteStream</span></code>
type's <code class="computeroutput"><span class="identifier">async_write_some</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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