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<title>async_write_at (1 of 4 overloads)</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.async_write_at.overload1"></a><a class="link" href="overload1.html" title="async_write_at (1 of 4 overloads)">async_write_at
(1 of 4 overloads)</a>
</h4></div></div></div>
<p>
Start an asynchronous operation to write all of the supplied data at the
specified offset.
</p>
<pre class="programlisting">template<
typename <a class="link" href="../AsyncRandomAccessWriteDevice.html" title="Buffer-oriented asynchronous random-access write device requirements">AsyncRandomAccessWriteDevice</a>,
typename <a class="link" href="../ConstBufferSequence.html" title="Constant buffer sequence requirements">ConstBufferSequence</a>,
typename <a class="link" href="../WriteHandler.html" title="Write handler requirements">WriteHandler</a>>
<a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_write_at(
AsyncRandomAccessWriteDevice & d,
uint64_t offset,
const ConstBufferSequence & buffers,
WriteHandler && handler);
</pre>
<p>
This function is used to asynchronously write a certain number of bytes
of data to a random access device at a specified offset. 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" style="list-style-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">
An error occurred.
</li>
</ul></div>
<p>
This operation is implemented in terms of zero or more calls to the device's
async_write_some_at function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
The program must ensure that the device performs no <span class="emphasis"><em>overlapping</em></span>
write operations (such as async_write_at, the device's async_write_some_at
function, or any other composed operations that perform writes) until this
operation completes. Operations are overlapping if the regions defined
by their offsets, and the numbers of bytes to write, intersect.
</p>
<h6>
<a name="boost_asio.reference.async_write_at.overload1.h0"></a>
<span class="phrase"><a name="boost_asio.reference.async_write_at.overload1.parameters"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_write_at.overload1.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">d</span></dt>
<dd><p>
The device to which the data is to be written. The type must support
the AsyncRandomAccessWriteDevice concept.
</p></dd>
<dt><span class="term">offset</span></dt>
<dd><p>
The offset at which the data will be written.
</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">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(
// Result of operation.
const boost::system::error_code& error,
// Number of bytes written from the buffers. If an error
// occurred, this will be less than the sum of the buffer sizes.
std::size_t bytes_transferred
);
</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">boost::asio::io_context::post()</code>.
</p>
</dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.async_write_at.overload1.h1"></a>
<span class="phrase"><a name="boost_asio.reference.async_write_at.overload1.example"></a></span><a class="link" href="overload1.html#boost_asio.reference.async_write_at.overload1.example">Example</a>
</h6>
<p>
To write a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</code></a>
function as follows:
</p>
<pre class="programlisting">boost::asio::async_write_at(d, 42, boost::asio::buffer(data, size), handler);
</pre>
<p>
See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput">buffer</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>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2018 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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