69 lines
2.7 KiB
HTML
69 lines
2.7 KiB
HTML
<html>
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<head>
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<title>BOOST_PP_CHECK_EMPTY</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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</head>
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<body>
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<div style="margin-left: 0px;"> The <b>BOOST_PP_CHECK_EMPTY</b> variadic macro
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checks to see if its variadic input is empty or not. It expands to 1 if its input
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is empty and expands to 0 if its input is not empty. The macro only exists when
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the compilation is at the C++20 level and the __VA_OPT__ construct is supported.</div>
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<h4>Usage</h4>
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<div class="code"> <b>BOOST_PP_CHECK_EMPTY</b>(<i>...</i>) <a href="../topics/variadic_macros.html#VNotation" target="_self"><sup>(v)</sup></a><br>
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</div>
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<h4>Arguments</h4>
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<dl>
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<dt>...<br>
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</dt>
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<dd> The <i>variadic data</i> to be checked for emptiness. </dd>
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</dl>
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<h4>Remarks</h4>
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<div>
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When the macro invocation BOOST_PP_VARIADIC_HAS_OPT() expands to 1, then this
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macro exists and can be invoked, otherwise this macro does not exist
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and attempting to invoke it will lead to a preprocessor error that the macro
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can not be found. Because of this condition the header file for including
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this macro includes the header file for the BOOST_PP_VARIADIC_HAS_OPT macro.<br>
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It is possible to pass data to this macro which expands to nothing, in which
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case this macro will expand to 1 just as if nothing has been passed.
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</div>
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<h4>See Also</h4>
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<ul>
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<li><a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a></li>
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</ul>
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<h4>Requirements</h4>
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<div> <b>Header:</b> <a href="../headers/facilities/check_empty.html"><boost/preprocessor/facilities/check_empty.hpp></a>
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</div>
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<h4>Sample Code</h4>
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<div>
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<pre>
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#include <<a href="../headers/facilities/check_empty.html">boost/preprocessor/facilities/check_empty.hpp</a>>
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# if <a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a>()
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#define DATA
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#define OBJECT OBJECT2
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#define OBJECT2
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#define FUNC(x) FUNC2(x)
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#define FUNC2(x)
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#define FUNC_GEN(x,y) (1,2,3)
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<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(DATA) // expands to 1
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<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(OBJECT) // expands to 1
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<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(FUNC(1)) // expands to 1
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<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(FUNC) // expands to 0
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<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(FUNC_GEN) // expands to 0
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#endif
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</pre>
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</div>
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<hr size="1">
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<div style="margin-left: 0px;"> <i></i><i><EFBFBD> Copyright Edward Diener 2019</i> </div>
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<div style="margin-left: 0px;">
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<p><small>Distributed under the Boost Software License, Version 1.0.
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(See accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
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or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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</div>
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</body>
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</html>
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