<link rel="home" href="index.html" title="Chapter 1. The Variadic Macro Data Library 1.9">
<link rel="up" href="header/boost/vmd/is_empty_hpp.html" title="Header <boost/vmd/is_empty.hpp>">
<link rel="prev" href="header/boost/vmd/is_empty_hpp.html" title="Header <boost/vmd/is_empty.hpp>">
-<link rel="next" href="header/boost/vmd/is_empty_array_hpp.html" title="Header <boost/vmd/is_empty_array.hpp>">
+<link rel="next" href="BOOST_VMD_IS_EMPTY_NO_OPT.html" title="Macro BOOST_VMD_IS_EMPTY_NO_OPT">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
</tr></table>
<hr>
<div class="spirit-nav">
-<a accesskey="p" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="
header/boost/vmd/is_empty_array_hpp.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="
BOOST_VMD_IS_EMPTY_NO_OPT.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="refentry">
<a name="BOOST_VMD_IS_EMPTY"></a><div class="titlepage"></div>
</span>BOOST_VMD_IS_EMPTY(...)</pre></div>
<div class="refsect1">
-<a name="idm46213760380352"></a><h2>Description</h2>
+<a name="idm45529680794432"></a><h2>Description</h2>
<p>The macro checks to see if the input is empty or not. It returns 1 if the input is empty, else returns 0.</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.</p>
-<p>The macro is not perfect, and can not be so. The problem area is if the input to be checked is a function-like macro name, in which case either a compiler error can result or a false result can occur.</p>
-<p>This macro is a replacement, using variadic macro support, for the undocumented macro BOOST_PP_IS_EMPTY in the Boost PP library. The code is taken from a posting by Paul Mensonides of a variadic version for BOOST_PP_IS_EMPTY, and changed in order to also support VC++.</p>
-<p>.... = variadic input, for VC++8 this must be a single parameter</p>
+<p>For all levels of C++ prior to C++20 the macro is not perfect, and can not be so. The problem area is if the input to be checked is a function-like macro name, in which case either a compiler error can result or a false result can occur.</p>
+<p>For C++20, with its support for the new <span class="bold"><strong>VA_OPT</strong></span> preprocessor construct, the macro will always work correctly no matter what the variadic input, and is therefore 100% reliable.</p>
+<p>This macro is a replacement, using variadic macro support, for the undocumented macro BOOST_PP_IS_EMPTY in the Boost PP library. The code is taken from a posting by Paul Mensonides of a variadic version for BOOST_PP_IS_EMPTY, and changed in order to also support VC++. The code for the C++20 implementation of the macro, using the <span class="bold"><strong>VA_OPT</strong></span> preprocessor construct, is the author's own and reuses code added to the Boost preprocessor library by this author.</p>
+<p>... = variadic input, for VC++8 this must be a single parameter</p>
<p>returns = 1 if the input is empty, 0 if it is not</p>
<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>
</div>
</tr></table>
<hr>
<div class="spirit-nav">
-<a accesskey="p" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="
header/boost/vmd/is_empty_array_hpp.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
+<a accesskey="p" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="header/boost/vmd/is_empty_hpp.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="
BOOST_VMD_IS_EMPTY_NO_OPT.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
projects / platform / upstream / boost.git / blobdiff