ext_compile_checks.html revision 1.1
1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter��29.��Compile Time Checks</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="extensions.html" title="Part��XII.�� Extensions" /><link rel="prev" href="bk01pt12pr03.html" title="" /><link rel="next" href="debug_mode.html" title="Chapter��30.��Debug Mode" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter��29.��Compile Time Checks</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt12pr03.html">Prev</a>��</td><th width="60%" align="center">Part��XII.�� 4 Extensions 5 6</th><td width="20%" align="right">��<a accesskey="n" href="debug_mode.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter��29.��Compile Time Checks"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.compile_checks"></a>Chapter��29.��Compile Time Checks</h2></div></div></div><p> 7 Also known as concept checking. 8 </p><p>In 1999, SGI added <span class="emphasis"><em>concept checkers</em></span> to their implementation 9 of the STL: code which checked the template parameters of 10 instantiated pieces of the STL, in order to insure that the parameters 11 being used met the requirements of the standard. For example, 12 the Standard requires that types passed as template parameters to 13 <code class="code">vector</code> be <span class="quote">���<span class="quote">Assignable</span>���</span> (which means what you think 14 it means). The checking was done during compilation, and none of 15 the code was executed at runtime. 16 </p><p>Unfortunately, the size of the compiler files grew significantly 17 as a result. The checking code itself was cumbersome. And bugs 18 were found in it on more than one occasion. 19 </p><p>The primary author of the checking code, Jeremy Siek, had already 20 started work on a replacement implementation. The new code has been 21 formally reviewed and accepted into 22 <a class="ulink" href="http://www.boost.org/libs/concept_check/concept_check.htm" target="_top">the 23 Boost libraries</a>, and we are pleased to incorporate it into the 24 GNU C++ library. 25 </p><p>The new version imposes a much smaller space overhead on the generated 26 object file. The checks are also cleaner and easier to read and 27 understand. 28 </p><p>They are off by default for all versions of GCC from 3.0 to 3.4 (the 29 latest release at the time of writing). 30 They can be enabled at configure time with 31 <a class="link" href="configure.html" title="Configure"><code class="literal">--enable-concept-checks</code></a>. 32 You can enable them on a per-translation-unit basis with 33 <code class="code">#define _GLIBCXX_CONCEPT_CHECKS</code> for GCC 3.4 and higher 34 (or with <code class="code">#define _GLIBCPP_CONCEPT_CHECKS</code> for versions 35 3.1, 3.2 and 3.3). 36 </p><p>Please note that the upcoming C++ standard has first-class 37 support for template parameter constraints based on concepts in the core 38 language. This will obviate the need for the library-simulated concept 39 checking described above. 40 </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt12pr03.html">Prev</a>��</td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right">��<a accesskey="n" href="debug_mode.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">��</td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top">��Chapter��30.��Debug Mode</td></tr></table></div></body></html> 41