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<title>Attributes of Primitive Components</title>
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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.
      </p>
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