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| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.operator.expect"></a><a class="link" href="expect.html" title="Expectation (a > b)">Expectation |
| (<code class="computeroutput"><span class="identifier">a</span> <span class="special">></span> |
| <span class="identifier">b</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.qi.reference.operator.expect.description"></a><h6> |
| <a name="id924046"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.description">Description</a> |
| </h6> |
| <p> |
| Like the <a class="link" href="sequence.html" title="Sequence (a >> b)">Sequence</a>, |
| the expectation operator, <code class="computeroutput"><span class="identifier">a</span> |
| <span class="special">></span> <span class="identifier">b</span></code>, |
| parses two or more operands (<code class="computeroutput"><span class="identifier">a</span></code>, |
| <code class="computeroutput"><span class="identifier">b</span></code>, ... etc.), in sequence: |
| </p> |
| <pre class="programlisting"><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span> <span class="special">></span> <span class="special">...</span> |
| </pre> |
| <p> |
| However, while the plain <a class="link" href="sequence.html" title="Sequence (a >> b)">Sequence</a> |
| simply returns a no-match (returns <code class="computeroutput"><span class="keyword">false</span></code>) |
| when one of the elements fail, the expectation: <code class="computeroutput"><span class="special">></span></code> |
| operator throws an <a class="link" href="expect.html#spirit.qi.reference.operator.expect.expectation_failure"><code class="computeroutput"><span class="identifier">expectation_failure</span></code></a><code class="computeroutput"><span class="special"><</span><span class="identifier">Iter</span><span class="special">></span></code> when the second or succeeding operands |
| (all operands except the first) fail to match. |
| </p> |
| <a name="spirit.qi.reference.operator.expect.header"></a><h6> |
| <a name="id928987"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/operator/expect.hpp> |
| </span><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_expect</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. |
| </p> |
| <a name="spirit.qi.reference.operator.expect.model_of"></a><h6> |
| <a name="id929062"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.model_of">Model of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../parser_concepts/naryparser.html" title="NaryParser"><code class="computeroutput"><span class="identifier">NaryParser</span></code></a> |
| </p></blockquote></div> |
| <div class="variablelist"> |
| <p class="title"><b>Notation</b></p> |
| <dl> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">b</span></code></span></dt> |
| <dd><p> |
| A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Iter</span></code></span></dt> |
| <dd><p> |
| A <a href="http://www.sgi.com/tech/stl/ForwardIterator.html" target="_top"><code class="computeroutput"><span class="identifier">ForwardIterator</span></code></a> type |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.qi.reference.operator.expect.expectation_failure"></a><h6> |
| <a name="id929164"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.expectation_failure">Expectation |
| Failure</a> |
| </h6> |
| <p> |
| When any operand, except the first, fail to match an <code class="computeroutput"><span class="identifier">expectation_failure</span><span class="special"><</span><span class="identifier">Iter</span><span class="special">></span></code> is thrown: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iter</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">expectation_failure</span> <span class="special">:</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span> |
| <span class="special">{</span> |
| <span class="identifier">Iter</span> <span class="identifier">first</span><span class="special">;</span> <span class="comment">// [first, last) iterator pointing |
| </span> <span class="identifier">Iter</span> <span class="identifier">last</span><span class="special">;</span> <span class="comment">// to the error position in the input. |
| </span> <code class="computeroutput"><span class="identifier">info</span></code> <span class="identifier">what_</span><span class="special">;</span> <span class="comment">// Information about the nature of the error. |
| </span><span class="special">};</span> |
| </pre> |
| <a name="spirit.qi.reference.operator.expect.expression_semantics"></a><h6> |
| <a name="id929317"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.expression_semantics">Expression |
| Semantics</a> |
| </h6> |
| <p> |
| Semantics of an expression is defined only where it differs from, or |
| is not defined in <a class="link" href="../parser_concepts/naryparser.html" title="NaryParser"><code class="computeroutput"><span class="identifier">NaryParser</span></code></a>. |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody><tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">a</span> <span class="special">></span> |
| <span class="identifier">b</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Match <code class="computeroutput"><span class="identifier">a</span></code> followed |
| by <code class="computeroutput"><span class="identifier">b</span></code>. If <code class="computeroutput"><span class="identifier">a</span></code> fails, no-match. If <code class="computeroutput"><span class="identifier">b</span></code> fails, throw an <code class="computeroutput"><span class="identifier">expectation_failure</span><span class="special"><</span><span class="identifier">Iter</span><span class="special">></span></code> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.operator.expect.attributes"></a><h6> |
| <a name="id929462"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.attributes">Attributes</a> |
| </h6> |
| <p> |
| See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound |
| Attribute Notation</a>. |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Attribute |
| </p> |
| </th> |
| </tr></thead> |
| <tbody><tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">a</span> <span class="special">></span> |
| <span class="identifier">b</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| |
| </p> |
| <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">tuple</span><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">></span> |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">A</span> |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">B</span> |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">Unused</span> |
| |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">>,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> |
| <span class="identifier">a</span><span class="special">:</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">>,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">></span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></pre> |
| <p> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.operator.expect.complexity"></a><h6> |
| <a name="id930146"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The overall complexity of the expectation parser is defined by the |
| sum of the complexities of its elements. The complexity of the expectation |
| operator itself is O(N), where N is the number of elements in the sequence. |
| </p></blockquote></div> |
| <a name="spirit.qi.reference.operator.expect.example"></a><h6> |
| <a name="id930167"></a> |
| <a class="link" href="expect.html#spirit.qi.reference.operator.expect.example">Example</a> |
| </h6> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> |
| section. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Some using declarations: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">expectation_failure</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| The code below uses an expectation operator to throw an <a class="link" href="expect.html#spirit.qi.reference.operator.expect.expectation_failure"><code class="computeroutput"><span class="identifier">expectation_failure</span></code></a> with a deliberate |
| parsing error when <code class="computeroutput"><span class="string">"o"</span></code> |
| is expected and <code class="computeroutput"><span class="string">"i"</span></code> |
| is what is found in the input. The <code class="computeroutput"><span class="keyword">catch</span></code> |
| block prints the information related to the error. Note: This is low |
| level code that demonstrates the <span class="emphasis"><em>bare-metal</em></span>. Typically, |
| you use an Error Handler to deal with the error. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">try</span> |
| <span class="special">{</span> |
| <span class="identifier">test_parser</span><span class="special">(</span><span class="string">"xi"</span><span class="special">,</span> <span class="identifier">char_</span><span class="special">(</span><span class="char">'x'</span><span class="special">)</span> <span class="special">></span> <span class="identifier">char_</span><span class="special">(</span><span class="char">'o'</span><span class="special">));</span> <span class="comment">// should throw an exception |
| </span><span class="special">}</span> |
| <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">expectation_failure</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"expected: "</span><span class="special">;</span> <span class="identifier">print_info</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">what_</span><span class="special">);</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"got: \""</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">last</span><span class="special">)</span> <span class="special"><<</span> <span class="char">'"'</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
| <p> |
| The code above will print: |
| </p> |
| <pre class="programlisting">expected: tag: literal-char, value: o |
| got: "i" |
| </pre> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2001-2010 Joel de Guzman, Hartmut Kaiser<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>) |
| </p> |
| </div></td> |
| </tr></table> |
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