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<title>The GNU Fortran Compiler: Internal representation of LOGICAL variables</title>

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<a name="Internal-representation-of-LOGICAL-variables"></a>
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Next: <a href="Thread_002dsafety-of-the-runtime-library.html#Thread_002dsafety-of-the-runtime-library" accesskey="n" rel="next">Thread-safety of the runtime library</a>, Previous: <a href="KIND-Type-Parameters.html#KIND-Type-Parameters" accesskey="p" rel="prev">KIND Type Parameters</a>, Up: <a href="Compiler-Characteristics.html#Compiler-Characteristics" accesskey="u" rel="up">Compiler Characteristics</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Internal-representation-of-LOGICAL-variables-1"></a>
<h3 class="section">5.2 Internal representation of LOGICAL variables</h3>
<a name="index-logical_002c-variable-representation"></a>

<p>The Fortran standard does not specify how variables of <code>LOGICAL</code>
type are represented, beyond requiring that <code>LOGICAL</code> variables
of default kind have the same storage size as default <code>INTEGER</code>
and <code>REAL</code> variables.  The GNU Fortran internal representation is
as follows.
</p>
<p>A <code>LOGICAL(KIND=N)</code> variable is represented as an
<code>INTEGER(KIND=N)</code> variable, however, with only two permissible
values: <code>1</code> for <code>.TRUE.</code> and <code>0</code> for
<code>.FALSE.</code>.  Any other integer value results in undefined behavior.
</p>
<p>See also <a href="Argument-passing-conventions.html#Argument-passing-conventions">Argument passing conventions</a> and <a href="Interoperability-with-C.html#Interoperability-with-C">Interoperability with C</a>.
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