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- <div class="titlepage"><div><div><h3 class="title">
- <a name="spirit_x3.abstracts.primitive_attributes"></a><a class="link" href="primitive_attributes.html" title="Attributes of Primitive Components">Attributes
- of Primitive Components</a>
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- <p>
- Parsers in <a href="http://boost-spirit.com" target="_top">Spirit</a> are fully
- attributed. <span class="emphasis"><em>Spirit.X3</em></span> parsers always <span class="emphasis"><em>expose</em></span>
- an attribute specific to their type. This is called <span class="emphasis"><em>synthesized
- attribute</em></span> as it is returned from a successful match representing
- the matched input sequence. For instance, numeric parsers, such as <code class="computeroutput"><span class="identifier">int_</span></code> or <code class="computeroutput"><span class="identifier">double_</span></code>,
- return the <code class="computeroutput"><span class="keyword">int</span></code> or <code class="computeroutput"><span class="keyword">double</span></code> value converted from the matched input
- sequence. Other primitive parser components have other intuitive attribute
- types, such as for instance <code class="computeroutput"><span class="identifier">int_</span></code>
- which has <code class="computeroutput"><span class="keyword">int</span></code>, or <code class="computeroutput"><span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span></code> which has <code class="computeroutput"><span class="keyword">char</span></code>.
- Primitive parsers apply the normal C++ convertibility rules: you can use
- any C++ type to receive the parsed value as long as the attribute type of
- the parser is convertible to the type provided. The following example shows
- how a synthesized parser attribute (the <code class="computeroutput"><span class="keyword">int</span></code>
- value) is extracted by calling the API function <code class="computeroutput"><span class="identifier">x3</span><span class="special">::</span><span class="identifier">parse</span></code>:
- </p>
- <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">value</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"123"</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">iterator</span> <span class="identifier">strbegin</span> <span class="special">=</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span>
- <span class="identifier">x3</span><span class="special">::</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">strbegin</span><span class="special">,</span> <span class="identifier">str</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">int_</span><span class="special">,</span> <span class="identifier">value</span><span class="special">);</span> <span class="comment">// value == 123</span>
- </pre>
- <p>
- For a full list of available parser primitives and their attribute types
- please see the sections X3 Parsers.
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