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144 lines
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<title>read_until (16 of 24 overloads)</title>
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="asio.reference.read_until.overload16"></a><a class="link" href="overload16.html" title="read_until (16 of 24 overloads)">read_until (16
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of 24 overloads)</a>
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</h4></div></div></div>
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<p>
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Read data into a streambuf until a function object indicates a match.
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</p>
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<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
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<span class="keyword">typename</span> <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a><span class="special">,</span>
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<span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
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<span class="keyword">typename</span> <span class="identifier">MatchCondition</span><span class="special">></span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">read_until</span><span class="special">(</span>
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<span class="identifier">SyncReadStream</span> <span class="special">&</span> <span class="identifier">s</span><span class="special">,</span>
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<span class="identifier">asio</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>
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<span class="identifier">MatchCondition</span> <span class="identifier">match_condition</span><span class="special">,</span>
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<span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span> <span class="special">&</span> <span class="identifier">ec</span><span class="special">,</span>
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<span class="keyword">typename</span> <span class="identifier">constraint</span><span class="special"><</span> <span class="identifier">is_match_condition</span><span class="special"><</span> <span class="identifier">MatchCondition</span> <span class="special">>::</span><span class="identifier">value</span> <span class="special">>::</span><span class="identifier">type</span> <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
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</pre>
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<p>
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This function is used to read data into the specified streambuf until a
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user-defined match condition function object, when applied to the data
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contained in the streambuf, indicates a successful match. The call will
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block until one of the following conditions is true:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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The match condition function object returns a std::pair where the second
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element evaluates to true.
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</li>
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<li class="listitem">
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An error occurred.
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</li>
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</ul></div>
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<p>
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This operation is implemented in terms of zero or more calls to the stream's
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read_some function. If the match condition function object already indicates
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a match, the function returns immediately.
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</p>
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<h6>
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<a name="asio.reference.read_until.overload16.h0"></a>
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<span><a name="asio.reference.read_until.overload16.parameters"></a></span><a class="link" href="overload16.html#asio.reference.read_until.overload16.parameters">Parameters</a>
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</h6>
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<div class="variablelist">
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<p class="title"><b></b></p>
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<dl>
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<dt><span class="term">s</span></dt>
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<dd><p>
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The stream from which the data is to be read. The type must support
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the SyncReadStream concept.
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</p></dd>
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<dt><span class="term">b</span></dt>
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<dd><p>
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A streambuf object into which the data will be read.
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</p></dd>
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<dt><span class="term">match_condition</span></dt>
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<dd>
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<p>
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The function object to be called to determine whether a match exists.
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The signature of the function object must be:
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</p>
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<pre class="programlisting"><span class="identifier">pair</span><span class="special"><</span><span class="identifier">iterator</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span> <span class="identifier">match_condition</span><span class="special">(</span><span class="identifier">iterator</span> <span class="identifier">begin</span><span class="special">,</span> <span class="identifier">iterator</span> <span class="identifier">end</span><span class="special">);</span>
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</pre>
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<p>
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where <code class="computeroutput"><span class="identifier">iterator</span></code> represents
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the type:
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</p>
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<pre class="programlisting"><span class="identifier">buffers_iterator</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="identifier">const_buffers_type</span><span class="special">></span>
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</pre>
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<p>
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The iterator parameters <code class="computeroutput"><span class="identifier">begin</span></code>
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and <code class="computeroutput"><span class="identifier">end</span></code> define the
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range of bytes to be scanned to determine whether there is a match.
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The <code class="computeroutput"><span class="identifier">first</span></code> member
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of the return value is an iterator marking one-past-the-end of the
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bytes that have been consumed by the match function. This iterator
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is used to calculate the <code class="computeroutput"><span class="identifier">begin</span></code>
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parameter for any subsequent invocation of the match condition. The
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<code class="computeroutput"><span class="identifier">second</span></code> member of
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the return value is true if a match has been found, false otherwise.
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</p>
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</dd>
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<dt><span class="term">ec</span></dt>
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<dd><p>
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Set to indicate what error occurred, if any.
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</p></dd>
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</dl>
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</div>
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<h6>
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<a name="asio.reference.read_until.overload16.h1"></a>
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<span><a name="asio.reference.read_until.overload16.return_value"></a></span><a class="link" href="overload16.html#asio.reference.read_until.overload16.return_value">Return
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Value</a>
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</h6>
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<p>
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The number of bytes in the streambuf's get area that have been fully consumed
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by the match function. Returns 0 if an error occurred.
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</p>
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<h6>
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<a name="asio.reference.read_until.overload16.h2"></a>
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<span><a name="asio.reference.read_until.overload16.remarks"></a></span><a class="link" href="overload16.html#asio.reference.read_until.overload16.remarks">Remarks</a>
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</h6>
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<p>
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After a successful read_until operation, the streambuf may contain additional
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data beyond that which matched the function object. An application will
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typically leave that data in the streambuf for a subsequent read_until
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operation to examine.
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</p>
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<p>
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The default implementation of the <code class="computeroutput"><span class="identifier">is_match_condition</span></code>
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type trait evaluates to true for function pointers and function objects
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with a <code class="computeroutput"><span class="identifier">result_type</span></code> typedef.
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It must be specialised for other user-defined function objects.
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</p>
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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</p>
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