1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Miscellaneous Notes</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../variant.html" title="Chapter 45. Boost.Variant"> 10<link rel="prev" href="design.html" title="Design Overview"> 11<link rel="next" href="refs.html" title="References"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="design.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../variant.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="refs.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="variant.misc"></a>Miscellaneous Notes</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="misc.html#variant.versus-any">Boost.Variant vs. Boost.Any</a></span></dt> 31<dt><span class="section"><a href="misc.html#id-1.3.46.7.3">Portability</a></span></dt> 32<dt><span class="section"><a href="misc.html#variant.troubleshooting">Troubleshooting</a></span></dt> 33<dt><span class="section"><a href="misc.html#variant.ack">Acknowledgments</a></span></dt> 34</dl></div> 35<div class="section"> 36<div class="titlepage"><div><div><h3 class="title"> 37<a name="variant.versus-any"></a>Boost.Variant vs. Boost.Any</h3></div></div></div> 38<p>As a discriminated union container, the Variant library shares many 39 of the same features of the <a class="link" href="../any.html" title="Chapter 4. Boost.Any">Any</a> library. 40 However, since neither library wholly encapsulates the features of the 41 other, one library cannot be generally recommended for use over the 42 other.</p> 43<p>That said, Boost.Variant has several advantages over Boost.Any, 44 such as: 45 46 </p> 47<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 48<li class="listitem">Boost.Variant guarantees the type of its content is one of a 49 finite, user-specified set of types.</li> 50<li class="listitem">Boost.Variant provides <span class="emphasis"><em>compile-time</em></span> 51 checked visitation of its content. (By contrast, the current version 52 of Boost.Any provides no visitation mechanism at all; but even if it 53 did, it would need to be checked at run-time.)</li> 54<li class="listitem">Boost.Variant enables generic visitation of its content. 55 (Even if Boost.Any did provide a visitation mechanism, it would enable 56 visitation only of explicitly-specified types.)</li> 57<li class="listitem">Boost.Variant offers an efficient, stack-based storage scheme 58 (avoiding the overhead of dynamic allocation).</li> 59</ul></div> 60<p> 61 62 </p> 63<p>Of course, Boost.Any has several advantages over Boost.Variant, 64 such as: 65 66 </p> 67<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 68<li class="listitem">Boost.Any, as its name implies, allows virtually any type for 69 its content, providing great flexibility.</li> 70<li class="listitem">Boost.Any provides the no-throw guarantee of exception safety 71 for its swap operation.</li> 72<li class="listitem">Boost.Any makes little use of template metaprogramming 73 techniques (avoiding potentially hard-to-read error messages and 74 significant compile-time processor and memory demands).</li> 75</ul></div> 76<p> 77 78 </p> 79</div> 80<div class="section"> 81<div class="titlepage"><div><div><h3 class="title"> 82<a name="id-1.3.46.7.3"></a>Portability</h3></div></div></div> 83<p>The library aims for 100% ANSI/ISO C++ conformance. However, this is 84 strictly impossible due to the inherently non-portable nature of the 85 Type Traits library's 86 <code class="computeroutput">type_with_alignment</code> facility. In 87 practice though, no compilers or platforms have been discovered where this 88 reliance on undefined behavior has been an issue.</p> 89<p>Additionally, significant effort has been expended to ensure proper 90 functioning despite various compiler bugs and other conformance problems. 91 To date the library testsuite has 92 been compiled and tested successfully on at least the following compilers 93 for basic and advanced functionality: 94 95 </p> 96<div class="informaltable"><table class="table"> 97<colgroup> 98<col> 99<col> 100<col> 101<col> 102<col> 103</colgroup> 104<thead><tr> 105<th> </th> 106<th>Basic</th> 107<th> 108 <code class="computeroutput">variant<T&></code> 109 </th> 110<th> 111 <a class="link" href="tutorial.html#variant.tutorial.over-sequence" title="Using a type sequence to specify bounded types"> 112 <code class="computeroutput">make_variant_over</code> 113 </a> 114 </th> 115<th> 116 <a class="link" href="tutorial.html#variant.tutorial.recursive.recursive-variant" title="Recursive types with make_recursive_variant"> 117 <code class="computeroutput">make_recursive_variant</code> 118 </a> 119 </th> 120</tr></thead> 121<tbody> 122<tr> 123<td>Borland C++ 5.5.1 and 5.6.4</td> 124<td>X</td> 125<td>X</td> 126<td> </td> 127<td> </td> 128</tr> 129<tr> 130<td>Comeau C++ 4.3.0</td> 131<td>X</td> 132<td>X</td> 133<td>X</td> 134<td>X</td> 135</tr> 136<tr> 137<td>GNU GCC 3.3.1</td> 138<td>X</td> 139<td>X</td> 140<td>X</td> 141<td>X</td> 142</tr> 143<tr> 144<td>GNU GCC 2.95.3</td> 145<td>X</td> 146<td>X</td> 147<td> </td> 148<td>X</td> 149</tr> 150<tr> 151<td>Intel C++ 7.0</td> 152<td>X</td> 153<td> </td> 154<td>X</td> 155<td>X</td> 156</tr> 157<tr> 158<td>Metrowerks CodeWarrior 8.3</td> 159<td>X</td> 160<td> </td> 161<td>X</td> 162<td>X</td> 163</tr> 164<tr> 165<td>Microsoft Visual C++ 7.1</td> 166<td>X</td> 167<td>X</td> 168<td>X</td> 169<td>X</td> 170</tr> 171<tr> 172<td>Microsoft Visual C++ 6 SP5 and 7</td> 173<td>X</td> 174<td> </td> 175<td> </td> 176<td> </td> 177</tr> 178</tbody> 179</table></div> 180<p> 181 182 </p> 183<p>Finally, the current state of the testsuite in CVS may be found on the 184 <a href="http://boost.sourceforge.net/regression-logs" target="_top">Test Summary</a> 185 page. Please note, however, that this page reports on day-to-day changes 186 to inter-release code found in the Boost CVS and thus likely does not 187 match the state of code found in Boost releases.</p> 188</div> 189<div class="section"> 190<div class="titlepage"><div><div><h3 class="title"> 191<a name="variant.troubleshooting"></a>Troubleshooting</h3></div></div></div> 192<div class="toc"><dl class="toc"> 193<dt><span class="section"><a href="misc.html#variant.troubleshooting.template-depth">"Template instantiation depth exceeds maximum"</a></span></dt> 194<dt><span class="section"><a href="misc.html#variant.troubleshooting.compiler-memory">"Internal heap limit reached"</a></span></dt> 195</dl></div> 196<p>Due to the heavy use of templates in the implementation of 197 <code class="computeroutput">variant</code>, it is not uncommon when compiling to encounter 198 problems related to template instantiaton depth, compiler memory, etc. This 199 section attempts to provide advice to common problems experienced on several 200 popular compilers.</p> 201<p>(This section is still in progress, with additional advice/feedback 202 welcome. Please post to the Boost-Users list with any useful experiences you 203 may have.)</p> 204<div class="section"> 205<div class="titlepage"><div><div><h4 class="title"> 206<a name="variant.troubleshooting.template-depth"></a>"Template instantiation depth exceeds maximum"</h4></div></div></div> 207<div class="toc"><dl class="toc"><dt><span class="section"><a href="misc.html#variant.troubleshooting.template-depth.gcc">GNU GCC</a></span></dt></dl></div> 208<div class="section"> 209<div class="titlepage"><div><div><h5 class="title"> 210<a name="variant.troubleshooting.template-depth.gcc"></a>GNU GCC</h5></div></div></div> 211<p>The compiler option 212 <code class="computeroutput">-ftemplate-depth-<span class="emphasis"><em>NN</em></span></code> can increase the 213 maximum allowed instantiation depth. (Try 214 <code class="computeroutput">-ftemplate-depth-50</code>.)</p> 215</div> 216</div> 217<div class="section"> 218<div class="titlepage"><div><div><h4 class="title"> 219<a name="variant.troubleshooting.compiler-memory"></a>"Internal heap limit reached"</h4></div></div></div> 220<div class="toc"><dl class="toc"><dt><span class="section"><a href="misc.html#variant.troubleshooting.compiler-memory.msvc">Microsoft Visual C++</a></span></dt></dl></div> 221<div class="section"> 222<div class="titlepage"><div><div><h5 class="title"> 223<a name="variant.troubleshooting.compiler-memory.msvc"></a>Microsoft Visual C++</h5></div></div></div> 224<p>The compiler option <code class="computeroutput">/Zm<span class="emphasis"><em>NNN</em></span></code> can 225 increase the memory allocation limit. The <code class="computeroutput">NNN</code> is a 226 scaling percentage (i.e., <code class="computeroutput">100</code> denotes the default limit). 227 (Try <code class="computeroutput">/Zm200</code>.)</p> 228</div> 229</div> 230</div> 231<div class="section"> 232<div class="titlepage"><div><div><h3 class="title"> 233<a name="variant.ack"></a>Acknowledgments</h3></div></div></div> 234<p>Eric Friedman and Itay Maman designed the initial submission; Eric was 235 the primary implementer.</p> 236<p>Eric is also the library maintainer and has expanded upon the initial 237 submission -- adding 238 <code class="computeroutput"><a class="link" href="../boost/make_recursive_variant.html" title="Class template make_recursive_variant">make_recursive_variant</a></code>, 239 <code class="computeroutput"><a class="link" href="../boost/make_variant_over.html" title="Class template make_variant_over">make_variant_over</a></code>, support for 240 reference content, etc.</p> 241<p>Andrei Alexandrescu's work in 242 [<a class="link" href="refs.html#variant.refs.ale01a">Ale01a</a>] 243and 244 [<a class="link" href="refs.html#variant.refs.ale02">Ale02</a>] 245inspired the library's design.</p> 246<p>Jeff Garland was the formal review manager.</p> 247<p>Douglas Gregor, 248Dave Abrahams, 249Anthony Williams, 250Fernando Cacciola, 251Joel de Guzman, 252Dirk Schreib, 253Brad King, 254Giovanni Bajo, 255Eugene Gladyshev, 256and others provided helpful feedback and suggestions to refine the semantics, 257interface, and implementation of the library.</p> 258</div> 259</div> 260<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 261<td align="left"></td> 262<td align="right"><div class="copyright-footer">Copyright © 2002, 2003 Eric Friedman, Itay Maman<br>Copyright © 2014-2020 Antony Polukhin<p>Distributed under the Boost Software License, Version 1.0. 263 (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at 264 <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 265 </p> 266</div></td> 267</tr></table> 268<hr> 269<div class="spirit-nav"> 270<a accesskey="p" href="design.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../variant.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="refs.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 271</div> 272</body> 273</html> 274
