123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119 |
- <html>
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
- <title>Index modifiers</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 1.9">
- <link rel="up" href="../vmd_modifiers.html" title="Macros with modifiers">
- <link rel="prev" href="vmd_modifiers_splitting.html" title="Splitting modifiers">
- <link rel="next" href="vmd_modifiers_single.html" title="Modifiers and the single-element sequence">
- </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="vmd_modifiers_splitting.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../vmd_modifiers.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="vmd_modifiers_single.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="variadic_macro_data.vmd_modifiers.vmd_modifiers_index"></a><a class="link" href="vmd_modifiers_index.html" title="Index modifiers">Index
- modifiers</a>
- </h3></div></div></div>
- <p>
- Index modifiers can be used with the BOOST_VMD_ELEM macro when identifier
- modifiers are being used. Index modifiers take two values:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- BOOST_VMD_RETURN_INDEX, return an index as a number, starting with 0,
- of the particular identifier modifier which matched, as part of the output
- of the BOOST_VMD_ELEM macro. If no particular identifier modifier matches,
- return emptiness as part of the output. The index number is determined
- purely by the order in which identifier modifiers are specified as optional
- parameters to BOOST_VMD_ELEM, whether singly as individual optional parameters
- or as a tuple of identifier modifiers.
- </li>
- <li class="listitem">
- BOOST_VMD_RETURN_NO_INDEX, do not return an index as part of the output.
- This is the default value and need only be used to override the BOOST_VMD_RETURN_INDEX
- value if it is specified.
- </li>
- </ul></div>
- <p>
- The BOOST_VMD_RETURN_INDEX tells the programmer which one of the identifier
- modifiers matched the element's data as an index. Some macro programmers
- find this more useful for the purposes of macro branching logic than branching
- using the actual name of the identifier itself.
- </p>
- <p>
- When the index modifier BOOST_VMD_RETURN_INDEX is specified, and identifier
- modifiers are specified along with the BOOST_VMD_TYPE_IDENTIFIER filter modifier,
- the output of BOOST_VMD_ELEM becomes a tuple of two elements. The first tuple
- element is the element matched and the last tuple element is the index, starting
- with 0, of the identifier modifier which matched. If an element is not matched
- both tuple elements are empty.
- </p>
- <p>
- If the splitting modifier BOOST_VMD_RETURN_AFTER is also specified then the
- output is a tuple of three elements. The first tuple element is the element
- matched, the second tuple element is the rest of the sequence after the matching
- element, and the last tuple element is the numeric index. If an element is
- not matched then all three tuple elements are empty.
- </p>
- <p>
- If identifier modifiers and the BOOST_VMD_TYPE_IDENTIFIER filter modifier
- are not specified as optional parameters, then if BOOST_VMD_RETURN_INDEX
- is specified it is ignored. If the splitting modifier BOOST_VMD_RETURN_ONLY_AFTER
- is specified, if BOOST_VMD_RETURN_INDEX is also specified it is ignored.
- </p>
- <p>
- Let's see how this works:
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">vmd</span><span class="special">/</span><span class="identifier">elem</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="preprocessor">#define</span> <span class="identifier">BOOST_VMD_REGISTER_ANAME</span> <span class="special">(</span><span class="identifier">ANAME</span><span class="special">)</span>
- <span class="preprocessor">#define</span> <span class="identifier">BOOST_VMD_REGISTER_APLACE</span> <span class="special">(</span><span class="identifier">APLACE</span><span class="special">)</span>
- <span class="preprocessor">#define</span> <span class="identifier">BOOST_VMD_REGISTER_ACOUNTRY</span> <span class="special">(</span><span class="identifier">ACOUNTRY</span><span class="special">)</span>
- <span class="preprocessor">#define</span> <span class="identifier">BOOST_VMD_DETECT_ANAME_ANAME</span>
- <span class="preprocessor">#define</span> <span class="identifier">BOOST_VMD_DETECT_APLACE_APLACE</span>
- <span class="preprocessor">#define</span> <span class="identifier">A_SEQUENCE</span> <span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">)</span> <span class="identifier">ANAME</span> <span class="special">(</span><span class="number">1</span><span class="special">)(</span><span class="number">2</span><span class="special">)</span> <span class="number">46</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="char">'ANAME'</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="identifier">emptiness</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_INDEX</span><span class="special">,</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="special">(,)</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_INDEX</span><span class="special">,</span><span class="identifier">ANAME</span><span class="special">,</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="char">'(ANAME,0)'</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_INDEX</span><span class="special">,(</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">,</span><span class="identifier">ANAME</span><span class="special">))</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="char">'(ANAME,2)'</span>
- </pre>
- <p>
- Used with splitting modifiers:
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">vmd</span><span class="special">/</span><span class="identifier">elem</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_INDEX</span><span class="special">,</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_AFTER</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="special">(,,)</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_INDEX</span><span class="special">,</span><span class="identifier">ANAME</span><span class="special">,</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_AFTER</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="char">'(ANAME,(1)(2) 46,0)'</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_INDEX</span><span class="special">,(</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">,</span><span class="identifier">ANAME</span><span class="special">),</span><span class="identifier">BOOST_VMD_RETURN_AFTER</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="char">'(ANAME,(1)(2) 46,2)'</span>
- <span class="identifier">BOOST_VMD_ELEM</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="identifier">A_SEQUENCE</span><span class="special">,</span><span class="identifier">BOOST_VMD_TYPE_IDENTIFIER</span><span class="special">,</span><span class="identifier">BOOST_VMD_RETURN_INDEX</span><span class="special">,(</span><span class="identifier">APLACE</span><span class="special">,</span><span class="identifier">ACOUNTRY</span><span class="special">,</span><span class="identifier">ANAME</span><span class="special">),</span><span class="identifier">BOOST_VMD_RETURN_ONLY_AFTER</span><span class="special">)</span> <span class="identifier">will</span> <span class="keyword">return</span> <span class="char">'(1)(2) 46'</span>
- </pre>
- </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="vmd_modifiers_splitting.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../vmd_modifiers.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="vmd_modifiers_single.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
- </div>
- </body>
- </html>
|