1 |
424 |
jeremybenn |
<?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>
|