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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.read.overload4"></a><a class="link" href="overload4.html" title="read (4 of 8 overloads)">read (4 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> <a class="link" href="../MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a><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="keyword">const</span> <span class="identifier">MutableBufferSequence</span> <span class="special">&amp;</span> <span class="identifier">buffers</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" style="list-style-type: disc; ">
  47 <li class="listitem">
  48               The supplied buffers are full. That is, the bytes transferred is equal
  49               to the sum of the buffer sizes.
  50             </li>
  51 <li class="listitem">
  52               The completion_condition function object returns 0.
  53             </li>
  54 </ul></div>
  55 <p>
  56           This operation is implemented in terms of zero or more calls to the stream's
  57           read_some function.
  58         </p>
  59 <h6>
  60 <a name="boost_asio.reference.read.overload4.h0"></a>
  61           <span class="phrase"><a name="boost_asio.reference.read.overload4.parameters"></a></span><a class="link" href="overload4.html#boost_asio.reference.read.overload4.parameters">Parameters</a>
  62         </h6>
  63 <div class="variablelist">
  64 <p class="title"><b></b></p>
  65 <dl class="variablelist">
  66 <dt><span class="term">s</span></dt>
  67 <dd><p>
  68                 The stream from which the data is to be read. The type must support
  69                 the SyncReadStream concept.
  70               </p></dd>
  71 <dt><span class="term">buffers</span></dt>
  72 <dd><p>
  73                 One or more buffers into which the data will be read. The sum of
  74                 the buffer sizes indicates the maximum number of bytes to read from
  75                 the stream.
  76               </p></dd>
  77 <dt><span class="term">completion_condition</span></dt>
  78 <dd>
  79 <p>
  80                 The function object to be called to determine whether the read operation
  81                 is complete. The signature of the function object must be:
  82 </p>
  83 <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>
  84   <span class="comment">// Result of latest read_some operation.</span>
  85   <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>
  86
  87   <span class="comment">// Number of bytes transferred so far.</span>
  88   <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span>
  89 <span class="special">);</span>
  90 </pre>
  91 <p>
  92                 A return value of 0 indicates that the read operation is complete.
  93                 A non-zero return value indicates the maximum number of bytes to
  94                 be read on the next call to the stream's read_some function.
  95               </p>
  96 </dd>
  97 <dt><span class="term">ec</span></dt>
  98 <dd><p>
  99                 Set to indicate what error occurred, if any.
 100               </p></dd>
 101 </dl>
 102 </div>
 103 <h6>
 104 <a name="boost_asio.reference.read.overload4.h1"></a>
 105           <span class="phrase"><a name="boost_asio.reference.read.overload4.return_value"></a></span><a class="link" href="overload4.html#boost_asio.reference.read.overload4.return_value">Return
 106           Value</a>
 107         </h6>
 108 <p>
 109           The number of bytes read. If an error occurs, returns the total number
 110           of bytes successfully transferred prior to the error.
 111         </p>
 112 </div>
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 115 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2014 Christopher M. Kohlhoff<p>
 116         Distributed under the Boost Software License, Version 1.0. (See accompanying
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