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<a href="../../ex/cpp_3A_3A/_23error.html" class="prev"><span>➤</span> #error</a>
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<h1>Directive #if</h1>
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| 286efd | 2012-03-24 | Henrik Grubbström (Grubba) | |
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<dl class='group--doc'>
<dt class='head--type'><span class='homogen--type'>Directive</span>
<span class='homogen--name'><b>#if</b></span>
</dt>
<dd><p><code class='directive'>#if</code></p></dd>
<dt class='head--doc'>Description</dt>
<dd class='body--doc'><p>The <a class='ms reference' href='../cpp_3A_3A.html'>#if</a> directive can evaluate simple expressions and, if
the expression is evaluates to true, "activate" the code block that
follows. The code block ends when an <a class='ms reference' href='../cpp_3A_3A.html'>#endif</a>, <a class='ms reference' href='../cpp_3A_3A.html'>#else</a>,
<a class='ms reference' href='../cpp_3A_3A.html'>#elseif</a> or <a class='ms reference' href='../cpp_3A_3A.html'>#elif</a> block is encountered at the same
nesting depth.</p>
<p> The <a class='ms reference' href='../cpp_3A_3A.html'>#if</a> expressions may include defines, integer, string
and float constants, <tt>?:</tt>, <tt>||</tt> and <tt>&&</tt> operations,
<tt>~</tt>, <tt>^</tt>, <tt>!</tt>, <tt>|</tt> and <tt>&</tt> operations,
<tt><</tt>, <tt>></tt>, <tt><=</tt>, <tt>>=</tt>, <tt>==</tt> and <tt>!=</tt> operations,
<tt>+</tt>, <tt>-</tt>, <tt>*</tt>, <tt>/</tt>, <tt><<</tt> and <tt>>></tt> operations
and paranthesis.</p>
<p> Strings may also be indexed with the <tt>[]</tt> index operator.
Finally there are three special "functions" available in <a class='ms reference' href='../cpp_3A_3A.html'>#if</a>
expressions; <a class='ms reference' href='../cpp_3A_3A/defined.html'>defined()</a>, <a class='ms reference' href='../cpp_3A_3A/efun.html'>efun()</a> and <a class='ms reference' href='../cpp_3A_3A/constant.html'>constant()</a>.</p>
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<dt class='head--doc'>See also</dt>
<dd class='body--doc'><p><a class='ms reference' href='../cpp_3A_3A.html'>#ifdef</a>, <a class='ms reference' href='../cpp_3A_3A.html'>#ifndef</a>, <a class='ms reference' href='../cpp_3A_3A.html'>#elif</a>, <a class='ms reference' href='../cpp_3A_3A.html'>#else</a>, <a class='ms reference' href='../cpp_3A_3A.html'>#endif</a>,
<a class='ms reference' href='../cpp_3A_3A/defined.html'>defined()</a>, <a class='ms reference' href='../cpp_3A_3A/constant.html'>constant()</a>, <a class='ms reference' href='../cpp_3A_3A/efun.html'>efun()</a></p>
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