1<html> 2<head> 3 <title>BOOST_PP_CHECK_EMPTY</title> 4 <link rel="stylesheet" type="text/css" href="../styles.css"> 5</head> 6<body> 7<div style="margin-left: 0px;"> The <b>BOOST_PP_CHECK_EMPTY</b> variadic macro 8checks to see if its variadic input is empty or not. It expands to 1 if its input 9is empty and expands to 0 if its input is not empty. The macro only exists when 10the compilation is at the C++20 level and the __VA_OPT__ construct is supported.</div> 11<h4>Usage</h4> 12<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> 13 </div> 14<h4>Arguments</h4> 15<dl> 16 <dt>...<br> 17</dt> 18 <dd> The <i>variadic data</i> to be checked for emptiness. </dd> 19</dl> 20<h4>Remarks</h4> 21<div> 22When the macro invocation BOOST_PP_VARIADIC_HAS_OPT() expands to 1, then this 23macro exists and can be invoked, otherwise this macro does not exist 24and attempting to invoke it will lead to a preprocessor error that the macro 25can not be found. Because of this condition the header file for including 26this macro includes the header file for the BOOST_PP_VARIADIC_HAS_OPT macro.<br> 27It is possible to pass data to this macro which expands to nothing, in which 28case this macro will expand to 1 just as if nothing has been passed. 29</div> 30<h4>See Also</h4> 31<ul> 32 <li><a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a></li> 33</ul> 34<h4>Requirements</h4> 35<div> <b>Header:</b> <a href="../headers/facilities/check_empty.html"><boost/preprocessor/facilities/check_empty.hpp></a> 36</div> 37<h4>Sample Code</h4> 38<div> 39<pre> 40#include <<a href="../headers/facilities/check_empty.html">boost/preprocessor/facilities/check_empty.hpp</a>> 41 42# if <a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a>() 43 44#define DATA 45#define OBJECT OBJECT2 46#define OBJECT2 47#define FUNC(x) FUNC2(x) 48#define FUNC2(x) 49#define FUNC_GEN(x,y) (1,2,3) 50 51<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(DATA) // expands to 1 52<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(OBJECT) // expands to 1 53<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(FUNC(1)) // expands to 1 54<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(FUNC) // expands to 0 55<a href="check_empty.html">BOOST_PP_CHECK_EMPTY</a>(FUNC_GEN) // expands to 0 56 57#endif 58</pre> 59</div> 60<hr size="1"> 61<div style="margin-left: 0px;"> <i></i><i>� Copyright Edward Diener 2019</i> </div> 62<div style="margin-left: 0px;"> 63<p><small>Distributed under the Boost Software License, Version 1.0. 64(See accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> 65or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p> 66</div> 67</body> 68</html> 69