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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 17. Debug Mode</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"/><meta name="keywords" content=" C++ , library , debug "/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="extensions.html" title="Part III. Extensions"/><link rel="prev" href="ext_compile_checks.html" title="Chapter 16. Compile Time Checks"/><link rel="next" href="bk01pt03ch17s02.html" title="Semantics"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 17. Debug Mode</th></tr><tr><td align="left"><a accesskey="p" href="ext_compile_checks.html">Prev</a> </td><th width="60%" align="center">Part III.
Extensions
</th><td align="right"> <a accesskey="n" href="bk01pt03ch17s02.html">Next</a></td></tr></table><hr/></div><div class="chapter" title="Chapter 17. Debug Mode"><div class="titlepage"><div><div><h1 class="title"><a id="manual.ext.debug_mode"/>Debug Mode</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="debug_mode.html#manual.ext.debug_mode.intro">Intro</a></span></dt><dt><span class="section"><a href="bk01pt03ch17s02.html">Semantics</a></span></dt><dt><span class="section"><a href="bk01pt03ch17s03.html">Using</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch17s03.html#debug_mode.using.mode">Using the Debug Mode</a></span></dt><dt><span class="section"><a href="bk01pt03ch17s03.html#debug_mode.using.specific">Using a Specific Debug Container</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch17s04.html">Design</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch17s04.html#debug_mode.design.goals">Goals</a></span></dt><dt><span class="section"><a href="bk01pt03ch17s04.html#debug_mode.design.methods">Methods</a></span></dt><dt><span class="section"><a href="bk01pt03ch17s04.html#debug_mode.design.other">Other Implementations</a></span></dt></dl></dd></dl></div><div class="section" title="Intro"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.debug_mode.intro"/>Intro</h2></div></div></div><p>
By default, libstdc++ is built with efficiency in mind, and
therefore performs little or no error checking that is not
required by the C++ standard. This means that programs that
incorrectly use the C++ standard library will exhibit behavior
that is not portable and may not even be predictable, because they
tread into implementation-specific or undefined behavior. To
detect some of these errors before they can become problematic,
libstdc++ offers a debug mode that provides additional checking of
library facilities, and will report errors in the use of libstdc++
as soon as they can be detected by emitting a description of the
problem to standard error and aborting the program. This debug
mode is available with GCC 3.4.0 and later versions.
</p><p>
The libstdc++ debug mode performs checking for many areas of the
C++ standard, but the focus is on checking interactions among
standard iterators, containers, and algorithms, including:
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p><span class="emphasis"><em>Safe iterators</em></span>: Iterators keep track of the
container whose elements they reference, so errors such as
incrementing a past-the-end iterator or dereferencing an iterator
that points to a container that has been destructed are diagnosed
immediately.</p></li><li class="listitem"><p><span class="emphasis"><em>Algorithm preconditions</em></span>: Algorithms attempt to
validate their input parameters to detect errors as early as
possible. For instance, the <code class="code">set_intersection</code>
algorithm requires that its iterator
parameters <code class="code">first1</code> and <code class="code">last1</code> form a valid
iterator range, and that the sequence
[<code class="code">first1</code>, <code class="code">last1</code>) is sorted according to
the same predicate that was passed
to <code class="code">set_intersection</code>; the libstdc++ debug mode will
detect an error if the sequence is not sorted or was sorted by a
different predicate.</p></li></ul></div></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="ext_compile_checks.html">Prev</a> </td><td align="center"><a accesskey="u" href="extensions.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch17s02.html">Next</a></td></tr><tr><td align="left" valign="top">Chapter 16. Compile Time Checks </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Semantics</td></tr></table></div></body></html>
