doc/html/boost_asio/reference/async_read/overload5.html

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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_asio.reference.async_read.overload5"></a><a class="link" href="overload5.html" title="async_read (5 of 8 overloads)">async_read
  28         (5 of 8 overloads)</a>
  29 </h4></div></div></div>
  30 <p>
  31           Start an asynchronous operation to read a certain amount of data from a
  32           stream.
  33         </p>
  34 <pre class="programlisting">template&lt;
  35     typename <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a>,
  36     typename Allocator,
  37     typename <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a> = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>&gt;
  38 <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_read(
  39     AsyncReadStream &amp; s,
  40     basic_streambuf&lt; Allocator &gt; &amp; b,
  41     ReadHandler &amp;&amp; handler = <a class="link" href="../asynchronous_operations.html#boost_asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a>);
  42 </pre>
  43 <p>
  44           This function is used to asynchronously read a certain number of bytes
  45           of data from a stream. The function call always returns immediately. The
  46           asynchronous operation will continue until one of the following conditions
  47           is true:
  48         </p>
  49 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  50 <li class="listitem">
  51               The supplied buffer is full (that is, it has reached maximum size).
  52             </li>
  53 <li class="listitem">
  54               An error occurred.
  55             </li>
  56 </ul></div>
  57 <p>
  58           This operation is implemented in terms of zero or more calls to the stream's
  59           async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
  60           The program must ensure that the stream performs no other read operations
  61           (such as async_read, the stream's async_read_some function, or any other
  62           composed operations that perform reads) until this operation completes.
  63         </p>
  64 <h6>
  65 <a name="boost_asio.reference.async_read.overload5.h0"></a>
  66           <span class="phrase"><a name="boost_asio.reference.async_read.overload5.parameters"></a></span><a class="link" href="overload5.html#boost_asio.reference.async_read.overload5.parameters">Parameters</a>
  67         </h6>
  68 <div class="variablelist">
  69 <p class="title"><b></b></p>
  70 <dl class="variablelist">
  71 <dt><span class="term">s</span></dt>
  72 <dd><p>
  73                 The stream from which the data is to be read. The type must support
  74                 the AsyncReadStream concept.
  75               </p></dd>
  76 <dt><span class="term">b</span></dt>
  77 <dd><p>
  78                 A <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a>
  79                 object into which the data will be read. Ownership of the streambuf
  80                 is retained by the caller, which must guarantee that it remains valid
  81                 until the handler is called.
  82               </p></dd>
  83 <dt><span class="term">handler</span></dt>
  84 <dd>
  85 <p>
  86                 The handler to be called when the read operation completes. Copies
  87                 will be made of the handler as required. The function signature of
  88                 the handler must be:
  89 </p>
  90 <pre class="programlisting">void handler(
  91   const boost::system::error_code&amp; error, // Result of operation.
  92
  93   std::size_t bytes_transferred           // Number of bytes copied into the
  94                                           // buffers. If an error occurred,
  95                                           // this will be the  number of
  96                                           // bytes successfully transferred
  97                                           // prior to the error.
  98 );
  99 </pre>
 100 <p>
 101                 Regardless of whether the asynchronous operation completes immediately
 102                 or not, the handler will not be invoked from within this function.
 103                 On immediate completion, invocation of the handler will be performed
 104                 in a manner equivalent to using <a class="link" href="../post.html" title="post"><code class="computeroutput">post</code></a>.
 105               </p>
 106 </dd>
 107 </dl>
 108 </div>
 109 <h6>
 110 <a name="boost_asio.reference.async_read.overload5.h1"></a>
 111           <span class="phrase"><a name="boost_asio.reference.async_read.overload5.remarks"></a></span><a class="link" href="overload5.html#boost_asio.reference.async_read.overload5.remarks">Remarks</a>
 112         </h6>
 113 <p>
 114           This overload is equivalent to calling:
 115         </p>
 116 <pre class="programlisting">boost::asio::async_read(
 117     s, b,
 118     boost::asio::transfer_all(),
 119     handler);
 120 </pre>
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