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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<title>Bison 3.0.4: Value Type</title>

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<body lang="en">
<a name="Value-Type"></a>
<div class="header">
<p>
Next: <a href="Multiple-Types.html#Multiple-Types" accesskey="n" rel="next">Multiple Types</a>, Up: <a href="Semantics.html#Semantics" accesskey="u" rel="up">Semantics</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Terms.html#Index-of-Terms" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Data-Types-of-Semantic-Values"></a>
<h4 class="subsection">3.4.1 Data Types of Semantic Values</h4>
<a name="index-semantic-value-type"></a>
<a name="index-value-type_002c-semantic"></a>
<a name="index-data-types-of-semantic-values"></a>
<a name="index-default-data-type"></a>

<p>In a simple program it may be sufficient to use the same data type for
the semantic values of all language constructs.  This was true in the
RPN and infix calculator examples (see <a href="RPN-Calc.html#RPN-Calc">Reverse Polish
Notation Calculator</a>).
</p>
<p>Bison normally uses the type <code>int</code> for semantic values if your
program uses the same data type for all language constructs.  To
specify some other type, define the <code>%define</code> variable
<code>api.value.type</code> like this:
</p>
<div class="example">
<pre class="example">%define api.value.type {double}
</pre></div>

<p>or
</p>
<div class="example">
<pre class="example">%define api.value.type {struct semantic_type}
</pre></div>

<p>The value of <code>api.value.type</code> should be a type name that does not
contain parentheses or square brackets.
</p>
<p>Alternatively, instead of relying of Bison&rsquo;s <code>%define</code> support, you may
rely on the C/C++ preprocessor and define <code>YYSTYPE</code> as a macro, like
this:
</p>
<div class="example">
<pre class="example">#define YYSTYPE double
</pre></div>

<p>This macro definition must go in the prologue of the grammar file
(see <a href="Grammar-Outline.html#Grammar-Outline">Outline of a Bison Grammar</a>).  If compatibility
with POSIX Yacc matters to you, use this.  Note however that Bison cannot
know <code>YYSTYPE</code>&rsquo;s value, not even whether it is defined, so there are
services it cannot provide.  Besides this works only for languages that have
a preprocessor.
</p>



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