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<title>async_write (2 of 4 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.async_write.overload2"></a><a class="link" href="overload2.html" title="async_write (2 of 4 overloads)">async_write
(2 of 4 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> <a class="link" href="../ConstBufferSequence.html" title="Constant buffer sequence requirements">ConstBufferSequence</a><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">CompletionCondition</span><span class="special">,</span>
<span class="keyword">typename</span> <a class="link" href="../WriteHandler.html" title="Write handler requirements">WriteHandler</a><span class="special">></span>
<span class="keyword">void</span> <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="keyword">const</span> <span class="identifier">ConstBufferSequence</span> <span class="special">&</span> <span class="identifier">buffers</span><span class="special">,</span>
<span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">,</span>
<span class="identifier">WriteHandler</span> <span class="identifier">handler</span><span class="special">);</span>
</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 buffers has been written. That is,
the bytes transferred is equal to the sum of the buffer sizes.
</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="bold"><strong>composed
operation</strong></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="boost_asio.reference.async_write.overload2.h0"></a>
<span><a name="boost_asio.reference.async_write.overload2.parameters"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_write.overload2.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">buffers</span></dt>
<dd><p>
One or more buffers containing the data to be written. Although the
buffers object may be copied as necessary, ownership of the underlying
memory blocks is retained by the caller, which must guarantee that
they remain 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"><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">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">// 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">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"><span class="keyword">void</span> <span class="identifier">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">error</span><span class="special">,</span> <span class="comment">// Result of operation.</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span> <span class="comment">// Number of bytes written from the</span>
<span class="comment">// buffers. If an error occurred,</span>
<span class="comment">// this will be less than the sum</span>
<span class="comment">// of the buffer sizes.</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>
<h6>
<a name="boost_asio.reference.async_write.overload2.h1"></a>
<span><a name="boost_asio.reference.async_write.overload2.example"></a></span><a class="link" href="overload2.html#boost_asio.reference.async_write.overload2.example">Example</a>
</h6>
<p>
To write a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a> function as follows:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">s</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">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">size</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">transfer_at_least</span><span class="special">(</span><span class="number">32</span><span class="special">),</span>
<span class="identifier">handler</span><span class="special">);</span>
</pre>
<p>
See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span class="identifier">buffer</span></code></a>
documentation for information on writing multiple buffers in one go, and
how to use it with arrays, boost::array or std::vector.
</p>
</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 © 2003-2012 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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