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<h2><span class="refentrytitle">Macro BOOST_VMD_ASSERT_IS_EMPTY</span></h2>
<p>BOOST_VMD_ASSERT_IS_EMPTY — Asserts that the input is empty. </p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="header/boost/vmd/assert_is_empty_hpp.html" title="Header &lt;boost/vmd/assert_is_empty.hpp&gt;">boost/vmd/assert_is_empty.hpp</a>&gt;
</span>BOOST_VMD_ASSERT_IS_EMPTY(...)</pre></div>
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<a name="idm45711066571744"></a><h2>Description</h2>
<p>The macro checks to see if the input is empty or not. If it is not empty, it forces a compiler error.</p>
<p>The macro is a variadic macro taking any input. For the VC++8 compiler (VS2005) the macro takes a single parameter of input to check and not variadic data.</p>
<p>The macro normally checks for emptiness only in debug mode. However an end-user can force the macro to check or not check by defining the macro BOOST_VMD_ASSERT_DATA to 1 or 0 respectively.</p>
<p>.... = variadic input, for VC++8 this must be a single parameter.</p>
<pre class="programlisting"><span class="identifier">returns</span> <span class="special">=</span> <span class="identifier">Normally</span> <span class="identifier">the</span> <span class="identifier">macro</span> <span class="identifier">returns</span> <span class="identifier">nothing</span><span class="special">.</span>
<span class="identifier">If</span> <span class="identifier">the</span> <span class="identifier">input</span> <span class="identifier">is</span> <span class="identifier">empty</span><span class="special">,</span> <span class="identifier">nothing</span> <span class="identifier">is</span> <span class="identifier">output</span><span class="special">.</span>
<span class="identifier">For</span> <span class="identifier">VC</span><span class="special">++</span><span class="special">,</span> <span class="identifier">because</span> <span class="identifier">there</span> <span class="identifier">is</span> <span class="identifier">no</span> <span class="identifier">sure</span> <span class="identifier">way</span> <span class="identifier">of</span> <span class="identifier">forcing</span>
<span class="identifier">a</span> <span class="identifier">compiler</span> <span class="identifier">error</span> <span class="identifier">from</span> <span class="identifier">within</span> <span class="identifier">a</span> <span class="identifier">macro</span> <span class="identifier">without</span> <span class="identifier">producing</span>
<span class="identifier">output</span><span class="special">,</span> <span class="keyword">if</span> <span class="identifier">the</span> <span class="identifier">input</span> <span class="identifier">is</span> <span class="identifier">not</span> <span class="identifier">empty</span> <span class="identifier">the</span>
<span class="identifier">macro</span> <span class="identifier">forces</span> <span class="identifier">a</span> <span class="identifier">compiler</span> <span class="identifier">error</span> <span class="identifier">by</span> <span class="identifier">outputting</span> <span class="identifier">invalid</span> <span class="identifier">C</span><span class="special">++</span><span class="special">.</span>
<span class="identifier">For</span> <span class="identifier">all</span> <span class="identifier">other</span> <span class="identifier">compilers</span> <span class="identifier">a</span> <span class="identifier">compiler</span> <span class="identifier">error</span> <span class="identifier">is</span> <span class="identifier">forced</span>
<span class="identifier">without</span> <span class="identifier">producing</span> <span class="identifier">output</span> <span class="keyword">if</span> <span class="identifier">the</span> <span class="identifier">input</span> <span class="identifier">is</span> <span class="identifier">not</span> <span class="identifier">empty</span><span class="special">.</span>
</pre>
<p>It is recommended to append BOOST_PP_EMPTY() to whatever input is being tested in order to avoid possible warning messages from some compilers about no parameters being passed to the macro when the input is truly empty. </p>
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