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<div class="section" title="buffer">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.buffer"></a><a class="link" href="buffer.html" title="buffer"> buffer</a>
</h3></div></div></div>
<p>
<a class="indexterm" name="id894283"></a>
The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span></code> function is used to create a buffer
object to represent raw memory, an array of POD elements, a vector of POD
elements, or a std::string.
</p>
<pre class="programlisting"><span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload1.html" title="buffer (1 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">mutable_buffer</span> <span class="special">&</span> <span class="identifier">b</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload1.html" title="buffer (1 of 22 overloads)">more...</a></em></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload2.html" title="buffer (2 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">mutable_buffer</span> <span class="special">&</span> <span class="identifier">b</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload2.html" title="buffer (2 of 22 overloads)">more...</a></em></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload3.html" title="buffer (3 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">const_buffer</span> <span class="special">&</span> <span class="identifier">b</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload3.html" title="buffer (3 of 22 overloads)">more...</a></em></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload4.html" title="buffer (4 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">const_buffer</span> <span class="special">&</span> <span class="identifier">b</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload4.html" title="buffer (4 of 22 overloads)">more...</a></em></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload5.html" title="buffer (5 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">void</span> <span class="special">*</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload5.html" title="buffer (5 of 22 overloads)">more...</a></em></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload6.html" title="buffer (6 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload6.html" title="buffer (6 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload7.html" title="buffer (7 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">PodType</span> <span class="special">(&</span><span class="identifier">data</span><span class="special">)[</span><span class="identifier">N</span><span class="special">]);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload7.html" title="buffer (7 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload8.html" title="buffer (8 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">PodType</span> <span class="special">(&</span><span class="identifier">data</span><span class="special">)[</span><span class="identifier">N</span><span class="special">],</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload8.html" title="buffer (8 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload9.html" title="buffer (9 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">PodType</span> <span class="special">(&</span><span class="identifier">data</span><span class="special">)[</span><span class="identifier">N</span><span class="special">]);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload9.html" title="buffer (9 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload10.html" title="buffer (10 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">PodType</span> <span class="special">(&</span><span class="identifier">data</span><span class="special">)[</span><span class="identifier">N</span><span class="special">],</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload10.html" title="buffer (10 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload11.html" title="buffer (11 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload11.html" title="buffer (11 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload12.html" title="buffer (12 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload12.html" title="buffer (12 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload13.html" title="buffer (13 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span> <span class="keyword">const</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload13.html" title="buffer (13 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload14.html" title="buffer (14 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span> <span class="keyword">const</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload14.html" title="buffer (14 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload15.html" title="buffer (15 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload15.html" title="buffer (15 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload16.html" title="buffer (16 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">N</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload16.html" title="buffer (16 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload17.html" title="buffer (17 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload17.html" title="buffer (17 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">></span>
<span class="identifier">mutable_buffers_1</span> <a class="link" href="buffer/overload18.html" title="buffer (18 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload18.html" title="buffer (18 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload19.html" title="buffer (19 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload19.html" title="buffer (19 of 22 overloads)">more...</a></em></span>
<span class="keyword">template</span><span class="special"><</span>
<span class="keyword">typename</span> <span class="identifier">PodType</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload20.html" title="buffer (20 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">PodType</span><span class="special">,</span> <span class="identifier">Allocator</span> <span class="special">></span> <span class="special">&</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload20.html" title="buffer (20 of 22 overloads)">more...</a></em></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload21.html" title="buffer (21 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&</span> <span class="identifier">data</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload21.html" title="buffer (21 of 22 overloads)">more...</a></em></span>
<span class="identifier">const_buffers_1</span> <a class="link" href="buffer/overload22.html" title="buffer (22 of 22 overloads)">buffer</a><span class="special">(</span>
<span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&</span> <span class="identifier">data</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size_in_bytes</span><span class="special">);</span>
<span class="emphasis"><em>» <a class="link" href="buffer/overload22.html" title="buffer (22 of 22 overloads)">more...</a></em></span>
</pre>
<p>
A buffer object represents a contiguous region of memory as a 2-tuple consisting
of a pointer and size in bytes. A tuple of the form <code class="computeroutput"><span class="special">{</span><span class="keyword">void</span><span class="special">*,</span> <span class="identifier">size_t</span><span class="special">}</span></code> specifies a mutable (modifiable) region
of memory. Similarly, a tuple of the form <code class="computeroutput"><span class="special">{</span><span class="keyword">const</span> <span class="keyword">void</span><span class="special">*,</span> <span class="identifier">size_t</span><span class="special">}</span></code> specifies a const (non-modifiable) region
of memory. These two forms correspond to the classes <a class="link" href="mutable_buffer.html" title="mutable_buffer"><code class="computeroutput"><span class="identifier">mutable_buffer</span></code></a> and <a class="link" href="const_buffer.html" title="const_buffer"><code class="computeroutput"><span class="identifier">const_buffer</span></code></a>, respectively. To mirror
C++'s conversion rules, a <a class="link" href="mutable_buffer.html" title="mutable_buffer"><code class="computeroutput"><span class="identifier">mutable_buffer</span></code></a> is implicitly convertible
to a <a class="link" href="const_buffer.html" title="const_buffer"><code class="computeroutput"><span class="identifier">const_buffer</span></code></a>,
and the opposite conversion is not permitted.
</p>
<p>
The simplest use case involves reading or writing a single buffer of a specified
size:
</p>
<pre class="programlisting"><span class="identifier">sock</span><span class="special">.</span><span class="identifier">send</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>
</pre>
<p>
In the above example, the return value of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span></code>
meets the requirements of the ConstBufferSequence concept so that it may
be directly passed to the socket's write function. A buffer created for modifiable
memory also meets the requirements of the MutableBufferSequence concept.
</p>
<p>
An individual buffer may be created from a builtin array, std::vector or
boost::array of POD elements. This helps prevent buffer overruns by automatically
determining the size of the buffer:
</p>
<pre class="programlisting"><span class="keyword">char</span> <span class="identifier">d1</span><span class="special">[</span><span class="number">128</span><span class="special">];</span>
<span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span> <span class="special">=</span> <span class="identifier">sock</span><span class="special">.</span><span class="identifier">receive</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">d1</span><span class="special">));</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">d2</span><span class="special">(</span><span class="number">128</span><span class="special">);</span>
<span class="identifier">bytes_transferred</span> <span class="special">=</span> <span class="identifier">sock</span><span class="special">.</span><span class="identifier">receive</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">d2</span><span class="special">));</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="number">128</span><span class="special">></span> <span class="identifier">d3</span><span class="special">;</span>
<span class="identifier">bytes_transferred</span> <span class="special">=</span> <span class="identifier">sock</span><span class="special">.</span><span class="identifier">receive</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">d3</span><span class="special">));</span>
</pre>
<p>
In all three cases above, the buffers created are exactly 128 bytes long.
Note that a vector is <span class="bold"><strong>never</strong></span> automatically
resized when creating or using a buffer. The buffer size is determined using
the vector's <code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>
member function, and not its capacity.
</p>
<a name="boost_asio.reference.buffer.accessing_buffer_contents"></a><h5>
<a name="id897469"></a>
<a class="link" href="buffer.html#boost_asio.reference.buffer.accessing_buffer_contents">Accessing
Buffer Contents</a>
</h5>
<p>
The contents of a buffer may be accessed using the boost::asio::buffer_size
and boost::asio::buffer_cast functions:
</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">mutable_buffer</span> <span class="identifier">b1</span> <span class="special">=</span> <span class="special">...;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">s1</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_size</span><span class="special">(</span><span class="identifier">b1</span><span class="special">);</span>
<span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">p1</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_cast</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">*>(</span><span class="identifier">b1</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">const_buffer</span> <span class="identifier">b2</span> <span class="special">=</span> <span class="special">...;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">s2</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_size</span><span class="special">(</span><span class="identifier">b2</span><span class="special">);</span>
<span class="keyword">const</span> <span class="keyword">void</span><span class="special">*</span> <span class="identifier">p2</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_cast</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">void</span><span class="special">*>(</span><span class="identifier">b2</span><span class="special">);</span>
</pre>
<p>
The boost::asio::buffer_cast function permits violations of type safety,
so uses of it in application code should be carefully considered.
</p>
<a name="boost_asio.reference.buffer.buffer_invalidation"></a><h5>
<a name="id897866"></a>
<a class="link" href="buffer.html#boost_asio.reference.buffer.buffer_invalidation">Buffer Invalidation</a>
</h5>
<p>
A buffer object does not have any ownership of the memory it refers to. It
is the responsibility of the application to ensure the memory region remains
valid until it is no longer required for an I/O operation. When the memory
is no longer available, the buffer is said to have been invalidated.
</p>
<p>
For the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span></code> overloads that accept an argument
of type std::vector, the buffer objects returned are invalidated by any vector
operation that also invalidates all references, pointers and iterators referring
to the elements in the sequence (C++ Std, 23.2.4)
</p>
<p>
For the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span></code> overloads that accept an argument
of type std::string, the buffer objects returned are invalidated according
to the rules defined for invalidation of references, pointers and iterators
referring to elements of the sequence (C++ Std, 21.3).
</p>
<a name="boost_asio.reference.buffer.buffer_arithmetic"></a><h5>
<a name="id897963"></a>
<a class="link" href="buffer.html#boost_asio.reference.buffer.buffer_arithmetic">Buffer Arithmetic</a>
</h5>
<p>
Buffer objects may be manipulated using simple arithmetic in a safe way which
helps prevent buffer overruns. Consider an array initialised as follows:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="number">6</span><span class="special">></span> <span class="identifier">a</span> <span class="special">=</span> <span class="special">{</span> <span class="char">'a'</span><span class="special">,</span> <span class="char">'b'</span><span class="special">,</span> <span class="char">'c'</span><span class="special">,</span> <span class="char">'d'</span><span class="special">,</span> <span class="char">'e'</span> <span class="special">};</span>
</pre>
<p>
A buffer object <code class="computeroutput"><span class="identifier">b1</span></code> created
using:
</p>
<pre class="programlisting"><span class="identifier">b1</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">a</span><span class="special">);</span>
</pre>
<p>
represents the entire array, <code class="computeroutput"><span class="special">{</span> <span class="char">'a'</span><span class="special">,</span> <span class="char">'b'</span><span class="special">,</span> <span class="char">'c'</span><span class="special">,</span>
<span class="char">'d'</span><span class="special">,</span> <span class="char">'e'</span> <span class="special">}</span></code>. An optional
second argument to the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span></code>
function may be used to limit the size, in bytes, of the buffer:
</p>
<pre class="programlisting"><span class="identifier">b2</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">a</span><span class="special">,</span> <span class="number">3</span><span class="special">);</span>
</pre>
<p>
such that <code class="computeroutput"><span class="identifier">b2</span></code> represents the
data <code class="computeroutput"><span class="special">{</span> <span class="char">'a'</span><span class="special">,</span> <span class="char">'b'</span><span class="special">,</span>
<span class="char">'c'</span> <span class="special">}</span></code>.
Even if the size argument exceeds the actual size of the array, the size
of the buffer object created will be limited to the array size.
</p>
<p>
An offset may be applied to an existing buffer to create a new one:
</p>
<pre class="programlisting"><span class="identifier">b3</span> <span class="special">=</span> <span class="identifier">b1</span> <span class="special">+</span> <span class="number">2</span><span class="special">;</span>
</pre>
<p>
where <code class="computeroutput"><span class="identifier">b3</span></code> will set to represent
<code class="computeroutput"><span class="special">{</span> <span class="char">'c'</span><span class="special">,</span> <span class="char">'d'</span><span class="special">,</span>
<span class="char">'e'</span> <span class="special">}</span></code>.
If the offset exceeds the size of the existing buffer, the newly created
buffer will be empty.
</p>
<p>
Both an offset and size may be specified to create a buffer that corresponds
to a specific range of bytes within an existing buffer:
</p>
<pre class="programlisting"><span class="identifier">b4</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">b1</span> <span class="special">+</span> <span class="number">1</span><span class="special">,</span> <span class="number">3</span><span class="special">);</span>
</pre>
<p>
so that <code class="computeroutput"><span class="identifier">b4</span></code> will refer to
the bytes <code class="computeroutput"><span class="special">{</span> <span class="char">'b'</span><span class="special">,</span> <span class="char">'c'</span><span class="special">,</span>
<span class="char">'d'</span> <span class="special">}</span></code>.
</p>
<a name="boost_asio.reference.buffer.buffers_and_scatter_gather_i_o"></a><h5>
<a name="id898609"></a>
<a class="link" href="buffer.html#boost_asio.reference.buffer.buffers_and_scatter_gather_i_o">Buffers
and Scatter-Gather I/O</a>
</h5>
<p>
To read or write using multiple buffers (i.e. scatter-gather I/O), multiple
buffer objects may be assigned into a container that supports the MutableBufferSequence
(for read) or ConstBufferSequence (for write) concepts:
</p>
<pre class="programlisting"><span class="keyword">char</span> <span class="identifier">d1</span><span class="special">[</span><span class="number">128</span><span class="special">];</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">d2</span><span class="special">(</span><span class="number">128</span><span class="special">);</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="number">128</span><span class="special">></span> <span class="identifier">d3</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="identifier">mutable_buffer</span><span class="special">,</span> <span class="number">3</span><span class="special">></span> <span class="identifier">bufs1</span> <span class="special">=</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">d1</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">d2</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">d3</span><span class="special">)</span> <span class="special">};</span>
<span class="identifier">bytes_transferred</span> <span class="special">=</span> <span class="identifier">sock</span><span class="special">.</span><span class="identifier">receive</span><span class="special">(</span><span class="identifier">bufs1</span><span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">const_buffer</span><span class="special">></span> <span class="identifier">bufs2</span><span class="special">;</span>
<span class="identifier">bufs2</span><span class="special">.</span><span class="identifier">push_back</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">d1</span><span class="special">));</span>
<span class="identifier">bufs2</span><span class="special">.</span><span class="identifier">push_back</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">d2</span><span class="special">));</span>
<span class="identifier">bufs2</span><span class="special">.</span><span class="identifier">push_back</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">d3</span><span class="special">));</span>
<span class="identifier">bytes_transferred</span> <span class="special">=</span> <span class="identifier">sock</span><span class="special">.</span><span class="identifier">send</span><span class="special">(</span><span class="identifier">bufs2</span><span class="special">);</span>
</pre>
<a name="boost_asio.reference.buffer.requirements"></a><h5>
<a name="id899204"></a>
<a class="link" href="buffer.html#boost_asio.reference.buffer.requirements">Requirements</a>
</h5>
<p>
<span class="bold"><strong>Header: </strong></span><code class="literal">boost/asio/buffer.hpp</code>
</p>
<p>
<span class="bold"><strong>Convenience header: </strong></span><code class="literal">boost/asio.hpp</code>
</p>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 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>
</div></td>
</tr></table>
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