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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.read.overload8"></a><a class="link" href="overload8.html" title="read (8 of 8 overloads)">read (8 of 8 overloads)</a>
  28 </h4></div></div></div>
  29 <p>
  30           Attempt to read a certain amount of data from a stream before returning.
  31         </p>
  32 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
  33     <span class="keyword">typename</span> <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a><span class="special">,</span>
  34     <span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
  35     <span class="keyword">typename</span> <span class="identifier">CompletionCondition</span><span class="special">&gt;</span>
  36 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">read</span><span class="special">(</span>
  37     <span class="identifier">SyncReadStream</span> <span class="special">&amp;</span> <span class="identifier">s</span><span class="special">,</span>
  38     <span class="identifier">basic_streambuf</span><span class="special">&lt;</span> <span class="identifier">Allocator</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">b</span><span class="special">,</span>
  39     <span class="identifier">CompletionCondition</span> <span class="identifier">completion_condition</span><span class="special">,</span>
  40     <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">&amp;</span> <span class="identifier">ec</span><span class="special">);</span>
  41 </pre>
  42 <p>
  43           This function is used to read a certain number of bytes of data from a
  44           stream. The call will block until one of the following conditions is true:
  45         </p>
  46 <div class="itemizedlist"><ul class="itemizedlist" type="disc">
  47 <li class="listitem">
  48               The supplied buffer is full (that is, it has reached maximum size).
  49             </li>
  50 <li class="listitem">
  51               The completion_condition function object returns 0.
  52             </li>
  53 </ul></div>
  54 <p>
  55           This operation is implemented in terms of zero or more calls to the stream's
  56           read_some function.
  57         </p>
  58 <h6>
  59 <a name="boost_asio.reference.read.overload8.h0"></a>
  60           <span><a name="boost_asio.reference.read.overload8.parameters"></a></span><a class="link" href="overload8.html#boost_asio.reference.read.overload8.parameters">Parameters</a>
  61         </h6>
  62 <div class="variablelist">
  63 <p class="title"><b></b></p>
  64 <dl>
  65 <dt><span class="term">s</span></dt>
  66 <dd><p>
  67                 The stream from which the data is to be read. The type must support
  68                 the SyncReadStream concept.
  69               </p></dd>
  70 <dt><span class="term">b</span></dt>
  71 <dd><p>
  72                 The <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput"><span class="identifier">basic_streambuf</span></code></a> object into
  73                 which the data will be read.
  74               </p></dd>
  75 <dt><span class="term">completion_condition</span></dt>
  76 <dd>
  77 <p>
  78                 The function object to be called to determine whether the read operation
  79                 is complete. The signature of the function object must be:
  80 </p>
  81 <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>
  82   <span class="comment">// Result of latest read_some operation.</span>
  83   <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">&amp;</span> <span class="identifier">error</span><span class="special">,</span>
  84
  85   <span class="comment">// Number of bytes transferred so far.</span>
  86   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
  87 <span class="special">);</span>
  88 </pre>
  89 <p>
  90                 A return value of 0 indicates that the read operation is complete.
  91                 A non-zero return value indicates the maximum number of bytes to
  92                 be read on the next call to the stream's read_some function.
  93               </p>
  94 </dd>
  95 <dt><span class="term">ec</span></dt>
  96 <dd><p>
  97                 Set to indicate what error occurred, if any.
  98               </p></dd>
  99 </dl>
 100 </div>
 101 <h6>
 102 <a name="boost_asio.reference.read.overload8.h1"></a>
 103           <span><a name="boost_asio.reference.read.overload8.return_value"></a></span><a class="link" href="overload8.html#boost_asio.reference.read.overload8.return_value">Return
 104           Value</a>
 105         </h6>
 106 <p>
 107           The number of bytes read. If an error occurs, returns the total number
 108           of bytes successfully transferred prior to the error.
 109         </p>
 110 </div>
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 112 <td align="left"></td>
 113 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2012 Christopher M. Kohlhoff<p>
 114         Distributed under the Boost Software License, Version 1.0. (See accompanying
 115         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>)
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