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213 lines
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<title>read_until (15 of 24 overloads)</title>
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<a accesskey="p" href="overload14.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../read_until.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../boost_asio.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload16.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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<div class="titlepage"><div><div><h4 class="title">
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<a name="boost_asio.reference.read_until.overload15"></a><a class="link" href="overload15.html" title="read_until (15 of 24 overloads)">read_until
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(15 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">template<
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typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>,
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typename Allocator,
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typename MatchCondition>
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std::size_t read_until(
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SyncReadStream & s,
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boost::asio::basic_streambuf< Allocator > & b,
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MatchCondition match_condition,
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typename constraint< is_match_condition< MatchCondition >::value >::type = 0);
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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" style="list-style-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="boost_asio.reference.read_until.overload15.h0"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload15.parameters"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.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 class="variablelist">
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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">pair<iterator, bool> match_condition(iterator begin, iterator end);
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</pre>
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<p>
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where <code class="computeroutput">iterator</code> represents the type:
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</p>
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<pre class="programlisting">buffers_iterator<basic_streambuf<Allocator>::const_buffers_type>
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</pre>
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<p>
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The iterator parameters <code class="computeroutput">begin</code> and <code class="computeroutput">end</code> define
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the range of bytes to be scanned to determine whether there is a
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match. The <code class="computeroutput">first</code> member of the return value is an iterator
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marking one-past-the-end of the bytes that have been consumed by
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the match function. This iterator is used to calculate the <code class="computeroutput">begin</code>
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parameter for any subsequent invocation of the match condition. The
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<code class="computeroutput">second</code> member of the return value is true if a match
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has been found, false otherwise.
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</p>
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</dd>
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</dl>
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</div>
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<h6>
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<a name="boost_asio.reference.read_until.overload15.h1"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload15.return_value"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.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.
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</p>
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<h6>
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<a name="boost_asio.reference.read_until.overload15.h2"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload15.exceptions"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.exceptions">Exceptions</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 class="variablelist">
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<dt><span class="term">boost::system::system_error</span></dt>
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<dd><p>
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Thrown on failure.
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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="boost_asio.reference.read_until.overload15.h3"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload15.remarks"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.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">is_match_condition</code> type
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trait evaluates to true for function pointers and function objects with
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a <code class="computeroutput">result_type</code> typedef. It must be specialised for other user-defined
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function objects.
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</p>
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<h6>
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<a name="boost_asio.reference.read_until.overload15.h4"></a>
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<span class="phrase"><a name="boost_asio.reference.read_until.overload15.examples"></a></span><a class="link" href="overload15.html#boost_asio.reference.read_until.overload15.examples">Examples</a>
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</h6>
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<p>
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To read data into a streambuf until whitespace is encountered:
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</p>
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<pre class="programlisting">typedef boost::asio::buffers_iterator<
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boost::asio::streambuf::const_buffers_type> iterator;
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std::pair<iterator, bool>
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match_whitespace(iterator begin, iterator end)
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{
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iterator i = begin;
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while (i != end)
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if (std::isspace(*i++))
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return std::make_pair(i, true);
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return std::make_pair(i, false);
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}
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...
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boost::asio::streambuf b;
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boost::asio::read_until(s, b, match_whitespace);
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</pre>
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<p>
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To read data into a streambuf until a matching character is found:
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</p>
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<pre class="programlisting">class match_char
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{
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public:
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explicit match_char(char c) : c_(c) {}
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template <typename Iterator>
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std::pair<Iterator, bool> operator()(
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Iterator begin, Iterator end) const
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{
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Iterator i = begin;
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while (i != end)
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if (c_ == *i++)
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return std::make_pair(i, true);
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return std::make_pair(i, false);
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}
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private:
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char c_;
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};
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namespace asio {
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template <> struct is_match_condition<match_char>
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: public boost::true_type {};
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} // namespace asio
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...
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boost::asio::streambuf b;
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boost::asio::read_until(s, b, match_char('a'));
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</pre>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
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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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</div></td>
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</tr></table>
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