58 lines
4.8 KiB
HTML
58 lines
4.8 KiB
HTML
<html>
|
||
<head>
|
||
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
|
||
<title>Macro BOOST_VMD_IS_EMPTY</title>
|
||
<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
|
||
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
|
||
<link rel="home" href="index.html" title="Chapter 1. The Variadic Macro Data Library 1.10">
|
||
<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="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>
|
||
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td>
|
||
<td align="center"><a href="../../../../index.html">Home</a></td>
|
||
<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td>
|
||
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
|
||
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
|
||
<td align="center"><a href="../../../../more/index.htm">More</a></td>
|
||
</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="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>
|
||
<div class="refnamediv">
|
||
<h2><span class="refentrytitle">Macro BOOST_VMD_IS_EMPTY</span></h2>
|
||
<p>BOOST_VMD_IS_EMPTY — Tests whether its input is empty or not. </p>
|
||
</div>
|
||
<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: <<a class="link" href="header/boost/vmd/is_empty_hpp.html" title="Header <boost/vmd/is_empty.hpp>">boost/vmd/is_empty.hpp</a>>
|
||
|
||
</span>BOOST_VMD_IS_EMPTY(...)</pre></div>
|
||
<div class="refsect1">
|
||
<a name="idm45711064926192"></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>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>
|
||
</div>
|
||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||
<td align="left"></td>
|
||
<td align="right"><div class="copyright-footer">Copyright © 2010-2017 Tropic Software
|
||
East Inc</div></td>
|
||
</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="BOOST_VMD_IS_EMPTY_NO_OPT.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
|
||
</div>
|
||
</body>
|
||
</html>
|