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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_asio.reference.async_write_at.overload4"></a><a class="link" href="overload4.html" title="async_write_at (4 of 4 overloads)">async_write_at |
| (4 of 4 overloads)</a> |
| </h4></div></div></div> |
| <p> |
| Start an asynchronous operation to write a certain amount of data at the |
| specified offset. |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> |
| <span class="keyword">typename</span> <a class="link" href="../AsyncRandomAccessWriteDevice.html" title="Buffer-oriented asynchronous random-access write device requirements">AsyncRandomAccessWriteDevice</a><span class="special">,</span> |
| <span class="keyword">typename</span> <span class="identifier">Allocator</span><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> |
| <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.return_type_of_an_initiating_function"><span class="emphasis"><em>void-or-deduced</em></span></a> <span class="identifier">async_write_at</span><span class="special">(</span> |
| <span class="identifier">AsyncRandomAccessWriteDevice</span> <span class="special">&</span> <span class="identifier">d</span><span class="special">,</span> |
| <span class="identifier">uint64_t</span> <span class="identifier">offset</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">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 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 <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 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.overload4.h0"></a> |
| <span class="phrase"><a name="boost_asio.reference.async_write_at.overload4.parameters"></a></span><a class="link" href="overload4.html#boost_asio.reference.async_write_at.overload4.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">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 |
| 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_at 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 device's async_write_some_at 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="comment">// Result of 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 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 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> |
| </div> |
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| <td align="right"><div class="copyright-footer">Copyright © 2003-2015 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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