diff options
Diffstat (limited to 'libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html')
| -rw-r--r-- | libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html b/libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html new file mode 100644 index 000000000..8fa7981de --- /dev/null +++ b/libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html @@ -0,0 +1,55 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Semantics</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><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="debug_mode.html" title="Chapter 17. Debug Mode"/><link rel="prev" href="debug_mode.html" title="Chapter 17. Debug Mode"/><link rel="next" href="bk01pt03ch17s03.html" title="Using"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Semantics</th></tr><tr><td align="left"><a accesskey="p" href="debug_mode.html">Prev</a> </td><th width="60%" align="center">Chapter 17. Debug Mode</th><td align="right"> <a accesskey="n" href="bk01pt03ch17s03.html">Next</a></td></tr></table><hr/></div><div class="section" title="Semantics"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.debug_mode.semantics"/>Semantics</h2></div></div></div><p> + </p><p>A program that uses the C++ standard library correctly + will maintain the same semantics under debug mode as it had with + the normal (release) library. All functional and exception-handling + guarantees made by the normal library also hold for the debug mode + library, with one exception: performance guarantees made by the + normal library may not hold in the debug mode library. For + instance, erasing an element in a <code class="code">std::list</code> is a + constant-time operation in normal library, but in debug mode it is + linear in the number of iterators that reference that particular + list. So while your (correct) program won't change its results, it + is likely to execute more slowly.</p><p>libstdc++ includes many extensions to the C++ standard library. In + some cases the extensions are obvious, such as the hashed + associative containers, whereas other extensions give predictable + results to behavior that would otherwise be undefined, such as + throwing an exception when a <code class="code">std::basic_string</code> is + constructed from a NULL character pointer. This latter category also + includes implementation-defined and unspecified semantics, such as + the growth rate of a vector. Use of these extensions is not + considered incorrect, so code that relies on them will not be + rejected by debug mode. However, use of these extensions may affect + the portability of code to other implementations of the C++ standard + library, and is therefore somewhat hazardous. For this reason, the + libstdc++ debug mode offers a "pedantic" mode (similar to + GCC's <code class="code">-pedantic</code> compiler flag) that attempts to emulate + the semantics guaranteed by the C++ standard. For + instance, constructing a <code class="code">std::basic_string</code> with a NULL + character pointer would result in an exception under normal mode or + non-pedantic debug mode (this is a libstdc++ extension), whereas + under pedantic debug mode libstdc++ would signal an error. To enable + the pedantic debug mode, compile your program with + both <code class="code">-D_GLIBCXX_DEBUG</code> + and <code class="code">-D_GLIBCXX_DEBUG_PEDANTIC</code> . + (N.B. In GCC 3.4.x and 4.0.0, due to a bug, + <code class="code">-D_GLIBXX_DEBUG_PEDANTIC</code> was also needed. The problem has + been fixed in GCC 4.0.1 and later versions.) </p><p>The following library components provide extra debugging + capabilities in debug mode:</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p><code class="code">std::basic_string</code> (no safe iterators and see note below)</p></li><li class="listitem"><p><code class="code">std::bitset</code></p></li><li class="listitem"><p><code class="code">std::deque</code></p></li><li class="listitem"><p><code class="code">std::list</code></p></li><li class="listitem"><p><code class="code">std::map</code></p></li><li class="listitem"><p><code class="code">std::multimap</code></p></li><li class="listitem"><p><code class="code">std::multiset</code></p></li><li class="listitem"><p><code class="code">std::set</code></p></li><li class="listitem"><p><code class="code">std::vector</code></p></li><li class="listitem"><p><code class="code">std::unordered_map</code></p></li><li class="listitem"><p><code class="code">std::unordered_multimap</code></p></li><li class="listitem"><p><code class="code">std::unordered_set</code></p></li><li class="listitem"><p><code class="code">std::unordered_multiset</code></p></li></ul></div><p>N.B. although there are precondition checks for some string operations, +e.g. <code class="code">operator[]</code>, +they will not always be run when using the <code class="code">char</code> and +<code class="code">wchar_t</code> specialisations (<code class="code">std::string</code> and +<code class="code">std::wstring</code>). This is because libstdc++ uses GCC's +<code class="code">extern template</code> extension to provide explicit instantiations +of <code class="code">std::string</code> and <code class="code">std::wstring</code>, and those +explicit instantiations don't include the debug-mode checks. If the +containing functions are inlined then the checks will run, so compiling +with <code class="code">-O1</code> might be enough to enable them. Alternatively +<code class="code">-D_GLIBCXX_EXTERN_TEMPLATE=0</code> will suppress the declarations +of the explicit instantiations and cause the functions to be instantiated +with the debug-mode checks included, but this is unsupported and not +guaranteed to work. For full debug-mode support you can use the +<code class="code">__gnu_debug::basic_string</code> debugging container directly, +which always works correctly. +</p></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="debug_mode.html">Prev</a> </td><td align="center"><a accesskey="u" href="debug_mode.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch17s03.html">Next</a></td></tr><tr><td align="left" valign="top">Chapter 17. Debug Mode </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Using</td></tr></table></div></body></html> |