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"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Concept Checking</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="diagnostics.html" title="Chapter��5.�� Diagnostics" /><link rel="prev" href="diagnostics.html" title="Chapter��5.�� Diagnostics" /><link rel="next" href="utilities.html" title="Chapter��6.�� Utilities" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Concept Checking</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="diagnostics.html">Prev</a>��</td><th width="60%" align="center">Chapter��5.�� 3 Diagnostics 4 5</th><td width="20%" align="right">��<a accesskey="n" href="utilities.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.diagnostics.concept_checking"></a>Concept Checking</h2></div></div></div><p> 6 In 1999, SGI added <span class="quote">���<span class="quote">concept checkers</span>���</span> to their 7 implementation of the STL: code which checked the template 8 parameters of instantiated pieces of the STL, in order to insure 9 that the parameters being used met the requirements of the 10 standard. For example, the Standard requires that types passed as 11 template parameters to <code class="classname">vector</code> be 12 "Assignable" (which means what you think it means). The 13 checking was done during compilation, and none of the code was 14 executed at runtime. 15 </p><p> 16 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> 20 The primary author of the checking code, Jeremy Siek, had already 21 started work on a replacement implementation. The new code was 22 formally reviewed and accepted into 23 <a class="link" href="http://www.boost.org/libs/concept_check/concept_check.htm" target="_top">the 24 Boost libraries</a>, and we are pleased to incorporate it into the 25 GNU C++ library. 26 </p><p> 27 The new version imposes a much smaller space overhead on the generated 28 object file. The checks are also cleaner and easier to read and 29 understand. 30 </p><p> 31 They are off by default for all versions of GCC. 32 They can be enabled at configure time with 33 <a class="link" href="configure.html" title="Configure"><code class="literal">--enable-concept-checks</code></a>. 34 You can enable them on a per-translation-unit basis with 35 <code class="literal">-D_GLIBCXX_CONCEPT_CHECKS</code>. 36 </p><p> 37 Please note that the checks are based on the requirements in the original 38 C++ standard, many of which were relaxed in the C++11 standard and so valid 39 C++11 code may be incorrectly rejected by the concept checks. Additionally, 40 some correct C++03 code might be rejected by the concept checks, 41 for example template argument types may need to be complete when used in 42 a template definition, rather than at the point of instantiation. 43 There are no plans to address these shortcomings. 44 </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="diagnostics.html">Prev</a>��</td><td width="20%" align="center"><a accesskey="u" href="diagnostics.html">Up</a></td><td width="40%" align="right">��<a accesskey="n" href="utilities.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter��5.�� 45 Diagnostics 46 47��</td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top">��Chapter��6.�� 48 Utilities 49 50</td></tr></table></div></body></html>