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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 V1.73.2" /><meta name="keywords" content=" ISO C++ , library " /><link rel="start" 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. Extensions</th><td width="20%" align="right"> <a accesskey="n" href="debug_mode.html">Next</a></td></tr></table><hr /></div><div class="chapter" lang="en" xml:lang="en"><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>
4 Also known as concept checking.
5 </p><p>In 1999, SGI added <span class="emphasis"><em>concept checkers</em></span> to their implementation
6 of the STL: code which checked the template parameters of
7 instantiated pieces of the STL, in order to insure that the parameters
8 being used met the requirements of the standard. For example,
9 the Standard requires that types passed as template parameters to
10 <code class="code">vector</code> be “<span class="quote">Assignable</span>” (which means what you think
11 it means). The checking was done during compilation, and none of
12 the code was executed at runtime.
13 </p><p>Unfortunately, the size of the compiler files grew significantly
14 as a result. The checking code itself was cumbersome. And bugs
15 were found in it on more than one occasion.
16 </p><p>The primary author of the checking code, Jeremy Siek, had already
17 started work on a replacement implementation. The new code has been
18 formally reviewed and accepted into
19 <a class="ulink" href="http://www.boost.org/libs/concept_check/concept_check.htm" target="_top">the
20 Boost libraries</a>, and we are pleased to incorporate it into the
22 </p><p>The new version imposes a much smaller space overhead on the generated
23 object file. The checks are also cleaner and easier to read and
25 </p><p>They are off by default for all versions of GCC from 3.0 to 3.4 (the
26 latest release at the time of writing).
27 They can be enabled at configure time with
28 <a class="ulink" href="../configopts.html" target="_top"><code class="literal">--enable-concept-checks</code></a>.
29 You can enable them on a per-translation-unit basis with
30 <code class="code">#define _GLIBCXX_CONCEPT_CHECKS</code> for GCC 3.4 and higher
31 (or with <code class="code">#define _GLIBCPP_CONCEPT_CHECKS</code> for versions
33 </p><p>Please note that the upcoming C++ standard has first-class
34 support for template parameter constraints based on concepts in the core
35 language. This will obviate the need for the library-simulated concept
36 checking described above.
37 </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>