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| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.karma.reference.operator.plus"></a><a class="link" href="plus.html" title="Plus (+a)">Plus (<code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.karma.reference.operator.plus.description"></a><h6> |
| <a name="id1092330"></a> |
| <a class="link" href="plus.html#spirit.karma.reference.operator.plus.description">Description</a> |
| </h6> |
| <p> |
| The Plus generator is used to repeat the execution of an embedded generator |
| one or more times. It succeeds if the embedded generator has been successfully |
| executed at least once. |
| </p> |
| <a name="spirit.karma.reference.operator.plus.header"></a><h6> |
| <a name="id1092346"></a> |
| <a class="link" href="plus.html#spirit.karma.reference.operator.plus.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/operator/plus.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">karma_plus</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.karma.reference.operator.plus.model_of"></a><h6> |
| <a name="id1092421"></a> |
| <a class="link" href="plus.html#spirit.karma.reference.operator.plus.model_of">Model of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a> |
| </p></blockquote></div> |
| <a name="spirit.karma.reference.operator.plus.expression_semantics"></a><h6> |
| <a name="id1092456"></a> |
| <a class="link" href="plus.html#spirit.karma.reference.operator.plus.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="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</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="special">+</span><span class="identifier">a</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The generator <code class="computeroutput"><span class="identifier">a</span></code> |
| is executed one or more times depending on the availability |
| of an attribute. The execution of <code class="computeroutput"><span class="identifier">a</span></code> |
| stops after the attribute values passed to the plus generator |
| are exhausted. The plus generator succeeds as long as its embedded |
| generator has been successfully executed at least once (unless |
| the underlying output stream reports an error). |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <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> |
| All failing iterations of the embedded generator will consume one element |
| from the supplied attribute. The overall <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code> will succeed as long as at least |
| one invocation of the embedded generator will succeed (unless the underlying |
| output stream reports an error). |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.karma.reference.operator.plus.attributes"></a><h6> |
| <a name="id1092583"></a> |
| <a class="link" href="plus.html#spirit.karma.reference.operator.plus.attributes">Attributes</a> |
| </h6> |
| <p> |
| See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.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="special">+</span><span class="identifier">a</span></code> |
| (unary <code class="computeroutput"><span class="special">+</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="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">a</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">Unused</span></pre> |
| <p> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| The table above uses <code class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> as a placeholder only. The notation |
| of <code class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> |
| stands for <span class="emphasis"><em>any STL container</em></span> holding elements |
| of type <code class="computeroutput"><span class="identifier">A</span></code>. |
| </p></td></tr> |
| </table></div> |
| <p> |
| The Plus generator will execute its embedded generator once for each |
| element in the provided container attribute as long as the embedded generator |
| succeeds. On each iteration it will pass the next consecutive element |
| from the container attribute to the embedded generator. Therefore the |
| number of iterations will not be larger than the number of elements in |
| the container passed as its attribute. An empty container will make the |
| plus generator fail. |
| </p> |
| <p> |
| It is important to note, that the plus generator does not perform any |
| buffering of the output generated by its embedded elements. That means |
| that any failing element generator might have already generated some |
| output, which is <span class="emphasis"><em>not</em></span> rolled back. |
| </p> |
| <div class="tip"><table border="0" summary="Tip"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../images/tip.png"></td> |
| <th align="left">Tip</th> |
| </tr> |
| <tr><td align="left" valign="top"> |
| <p> |
| The simplest way to force a plus generator to behave as if it did buffering |
| is to wrap it into a buffering directive (see <a class="link" href="../directive/buffer.html" title="Temporary Output Buffering (buffer[])"><code class="computeroutput"><span class="identifier">buffer</span></code></a>): |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">buffer</span><span class="special">[+</span><span class="identifier">a</span><span class="special">]</span></pre> |
| <p> |
| </p> |
| <p> |
| which will <span class="emphasis"><em>not</em></span> generate any output in case of |
| a failing generator <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>. The expression: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="special">+(</span><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">])</span></pre> |
| <p> |
| </p> |
| <p> |
| will not generate any partial output from a generator <code class="computeroutput"><span class="identifier">a</span></code> if it fails generating in the middle |
| of its output. The overall expression will still generate the output |
| as produced by all successful invocations of the generator <code class="computeroutput"><span class="identifier">a</span></code>. |
| </p> |
| </td></tr> |
| </table></div> |
| <a name="spirit.karma.reference.operator.plus.complexity"></a><h6> |
| <a name="id1092925"></a> |
| <a class="link" href="plus.html#spirit.karma.reference.operator.plus.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The overall complexity of the plus generator is defined by the complexity |
| of its embedded generator multiplied by the number of executed iterations. |
| The complexity of the plus generator itself is O(N), where N is the |
| number of elements in the container passed as its attribute. |
| </p></blockquote></div> |
| <a name="spirit.karma.reference.operator.plus.example"></a><h6> |
| <a name="id1092945"></a> |
| <a class="link" href="plus.html#spirit.karma.reference.operator.plus.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="../karma_basics.html#spirit.karma.reference.karma_basics.examples">Basics Examples</a> |
| section. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Some includes: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><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">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></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">phoenix_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></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">phoenix_operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span> |
| </pre> |
| <p> |
| </p> |
| <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">karma</span><span class="special">::</span><span class="identifier">double_</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">karma</span><span class="special">::</span><span class="identifier">space</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Basic usage of a plus generator: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v1</span><span class="special">;</span> |
| <span class="identifier">v1</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">1.0</span><span class="special">);</span> |
| <span class="identifier">v1</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">2.0</span><span class="special">);</span> |
| <span class="identifier">v1</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">3.0</span><span class="special">);</span> |
| <span class="identifier">test_generator_attr_delim</span><span class="special">(</span><span class="string">"1.0 2.0 3.0 "</span><span class="special">,</span> <span class="special">+</span><span class="identifier">double_</span><span class="special">,</span> <span class="identifier">space</span><span class="special">,</span> <span class="identifier">v1</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| A more sophisticated use case showing how to leverage the fact that plus |
| is failing for empty containers passed as its attribute: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v2</span><span class="special">;</span> <span class="comment">// empty container |
| </span><span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"empty"</span><span class="special">,</span> <span class="special">+</span><span class="identifier">double_</span> <span class="special">|</span> <span class="string">"empty"</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| </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> |
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