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+<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Design</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><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 Documentation" /><link rel="up" href="debug_mode.html" title="Chapter 30. Debug Mode" /><link rel="prev" href="bk01pt12ch30s03.html" title="Using" /><link rel="next" href="parallel_mode.html" title="Chapter 31. Parallel Mode" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Design</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt12ch30s03.html">Prev</a> </td><th width="60%" align="center">Chapter 30. Debug Mode</th><td width="20%" align="right"> <a accesskey="n" href="parallel_mode.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.debug_mode.design"></a>Design</h2></div></div></div><p>
+ </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.debug_mode.design.goals"></a>Goals</h3></div></div></div><p>
+ </p><p> The libstdc++ debug mode replaces unsafe (but efficient) standard
+ containers and iterators with semantically equivalent safe standard
+ containers and iterators to aid in debugging user programs. The
+ following goals directed the design of the libstdc++ debug mode:</p><div class="itemizedlist"><ul type="disc"><li><p><span class="emphasis"><em>Correctness</em></span>: the libstdc++ debug mode must not change
+ the semantics of the standard library for all cases specified in
+ the ANSI/ISO C++ standard. The essence of this constraint is that
+ any valid C++ program should behave in the same manner regardless
+ of whether it is compiled with debug mode or release mode. In
+ particular, entities that are defined in namespace std in release
+ mode should remain defined in namespace std in debug mode, so that
+ legal specializations of namespace std entities will remain
+ valid. A program that is not valid C++ (e.g., invokes undefined
+ behavior) is not required to behave similarly, although the debug
+ mode will abort with a diagnostic when it detects undefined
+ behavior.</p></li><li><p><span class="emphasis"><em>Performance</em></span>: the additional of the libstdc++ debug mode
+ must not affect the performance of the library when it is compiled
+ in release mode. Performance of the libstdc++ debug mode is
+ secondary (and, in fact, will be worse than the release
+ mode).</p></li><li><p><span class="emphasis"><em>Usability</em></span>: the libstdc++ debug mode should be easy to
+ use. It should be easily incorporated into the user's development
+ environment (e.g., by requiring only a single new compiler switch)
+ and should produce reasonable diagnostics when it detects a
+ problem with the user program. Usability also involves detection
+ of errors when using the debug mode incorrectly, e.g., by linking
+ a release-compiled object against a debug-compiled object if in
+ fact the resulting program will not run correctly.</p></li><li><p><span class="emphasis"><em>Minimize recompilation</em></span>: While it is expected that
+ users recompile at least part of their program to use debug
+ mode, the amount of recompilation affects the
+ detect-compile-debug turnaround time. This indirectly affects the
+ usefulness of the debug mode, because debugging some applications
+ may require rebuilding a large amount of code, which may not be
+ feasible when the suspect code may be very localized. There are
+ several levels of conformance to this requirement, each with its
+ own usability and implementation characteristics. In general, the
+ higher-numbered conformance levels are more usable (i.e., require
+ less recompilation) but are more complicated to implement than
+ the lower-numbered conformance levels.
+ </p><div class="orderedlist"><ol type="1"><li><p><span class="emphasis"><em>Full recompilation</em></span>: The user must recompile his or
+ her entire application and all C++ libraries it depends on,
+ including the C++ standard library that ships with the
+ compiler. This must be done even if only a small part of the
+ program can use debugging features.</p></li><li><p><span class="emphasis"><em>Full user recompilation</em></span>: The user must recompile
+ his or her entire application and all C++ libraries it depends
+ on, but not the C++ standard library itself. This must be done
+ even if only a small part of the program can use debugging
+ features. This can be achieved given a full recompilation
+ system by compiling two versions of the standard library when
+ the compiler is installed and linking against the appropriate
+ one, e.g., a multilibs approach.</p></li><li><p><span class="emphasis"><em>Partial recompilation</em></span>: The user must recompile the
+ parts of his or her application and the C++ libraries it
+ depends on that will use the debugging facilities
+ directly. This means that any code that uses the debuggable
+ standard containers would need to be recompiled, but code
+ that does not use them (but may, for instance, use IOStreams)
+ would not have to be recompiled.</p></li><li><p><span class="emphasis"><em>Per-use recompilation</em></span>: The user must recompile the
+ parts of his or her application and the C++ libraries it
+ depends on where debugging should occur, and any other code
+ that interacts with those containers. This means that a set of
+ translation units that accesses a particular standard
+ container instance may either be compiled in release mode (no
+ checking) or debug mode (full checking), but must all be
+ compiled in the same way; a translation unit that does not see
+ that standard container instance need not be recompiled. This
+ also means that a translation unit <span class="emphasis"><em>A</em></span> that contains a
+ particular instantiation
+ (say, <code class="code">std::vector<int></code>) compiled in release
+ mode can be linked against a translation unit <span class="emphasis"><em>B</em></span> that
+ contains the same instantiation compiled in debug mode (a
+ feature not present with partial recompilation). While this
+ behavior is technically a violation of the One Definition
+ Rule, this ability tends to be very important in
+ practice. The libstdc++ debug mode supports this level of
+ recompilation. </p></li><li><p><span class="emphasis"><em>Per-unit recompilation</em></span>: The user must only
+ recompile the translation units where checking should occur,
+ regardless of where debuggable standard containers are
+ used. This has also been dubbed "<code class="code">-g</code> mode",
+ because the <code class="code">-g</code> compiler switch works in this way,
+ emitting debugging information at a per--translation-unit
+ granularity. We believe that this level of recompilation is in
+ fact not possible if we intend to supply safe iterators, leave
+ the program semantics unchanged, and not regress in
+ performance under release mode because we cannot associate
+ extra information with an iterator (to form a safe iterator)
+ without either reserving that space in release mode
+ (performance regression) or allocating extra memory associated
+ with each iterator with <code class="code">new</code> (changes the program
+ semantics).</p></li></ol></div><p>
+ </p></li></ul></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.debug_mode.design.methods"></a>Methods</h3></div></div></div><p>
+ </p><p>This section provides an overall view of the design of the
+ libstdc++ debug mode and details the relationship between design
+ decisions and the stated design goals.</p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.wrappers"></a>The Wrapper Model</h4></div></div></div><p>The libstdc++ debug mode uses a wrapper model where the debugging
+ versions of library components (e.g., iterators and containers) form
+ a layer on top of the release versions of the library
+ components. The debugging components first verify that the operation
+ is correct (aborting with a diagnostic if an error is found) and
+ will then forward to the underlying release-mode container that will
+ perform the actual work. This design decision ensures that we cannot
+ regress release-mode performance (because the release-mode
+ containers are left untouched) and partially enables <a class="ulink" href="#mixing" target="_top">mixing debug and release code</a> at link time,
+ although that will not be discussed at this time.</p><p>Two types of wrappers are used in the implementation of the debug
+ mode: container wrappers and iterator wrappers. The two types of
+ wrappers interact to maintain relationships between iterators and
+ their associated containers, which are necessary to detect certain
+ types of standard library usage errors such as dereferencing
+ past-the-end iterators or inserting into a container using an
+ iterator from a different container.</p><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="debug_mode.design.methods.safe_iter"></a>Safe Iterators</h5></div></div></div><p>Iterator wrappers provide a debugging layer over any iterator that
+ is attached to a particular container, and will manage the
+ information detailing the iterator's state (singular,
+ dereferenceable, etc.) and tracking the container to which the
+ iterator is attached. Because iterators have a well-defined, common
+ interface the iterator wrapper is implemented with the iterator
+ adaptor class template <code class="code">__gnu_debug::_Safe_iterator</code>,
+ which takes two template parameters:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="code">Iterator</code>: The underlying iterator type, which must
+ be either the <code class="code">iterator</code> or <code class="code">const_iterator</code>
+ typedef from the sequence type this iterator can reference.</p></li><li><p><code class="code">Sequence</code>: The type of sequence that this iterator
+ references. This sequence must be a safe sequence (discussed below)
+ whose <code class="code">iterator</code> or <code class="code">const_iterator</code> typedef
+ is the type of the safe iterator.</p></li></ul></div></div><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="debug_mode.design.methods.safe_seq"></a>Safe Sequences (Containers)</h5></div></div></div><p>Container wrappers provide a debugging layer over a particular
+ container type. Because containers vary greatly in the member
+ functions they support and the semantics of those member functions
+ (especially in the area of iterator invalidation), container
+ wrappers are tailored to the container they reference, e.g., the
+ debugging version of <code class="code">std::list</code> duplicates the entire
+ interface of <code class="code">std::list</code>, adding additional semantic
+ checks and then forwarding operations to the
+ real <code class="code">std::list</code> (a public base class of the debugging
+ version) as appropriate. However, all safe containers inherit from
+ the class template <code class="code">__gnu_debug::_Safe_sequence</code>,
+ instantiated with the type of the safe container itself (an instance
+ of the curiously recurring template pattern).</p><p>The iterators of a container wrapper will be
+ <a class="ulink" href="#safe_iterator" target="_top">safe iterators</a> that reference sequences
+ of this type and wrap the iterators provided by the release-mode
+ base class. The debugging container will use only the safe
+ iterators within its own interface (therefore requiring the user to
+ use safe iterators, although this does not change correct user
+ code) and will communicate with the release-mode base class with
+ only the underlying, unsafe, release-mode iterators that the base
+ class exports.</p><p> The debugging version of <code class="code">std::list</code> will have the
+ following basic structure:</p><pre class="programlisting">
+template<typename _Tp, typename _Allocator = allocator<_Tp>
+ class debug-list :
+ public release-list<_Tp, _Allocator>,
+ public __gnu_debug::_Safe_sequence<debug-list<_Tp, _Allocator> >
+ {
+ typedef release-list<_Tp, _Allocator> _Base;
+ typedef debug-list<_Tp, _Allocator> _Self;
+
+ public:
+ typedef __gnu_debug::_Safe_iterator<typename _Base::iterator, _Self> iterator;
+ typedef __gnu_debug::_Safe_iterator<typename _Base::const_iterator, _Self> const_iterator;
+
+ // duplicate std::list interface with debugging semantics
+ };
+</pre></div></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.precond"></a>Precondition Checking</h4></div></div></div><p>The debug mode operates primarily by checking the preconditions of
+ all standard library operations that it supports. Preconditions that
+ are always checked (regardless of whether or not we are in debug
+ mode) are checked via the <code class="code">__check_xxx</code> macros defined
+ and documented in the source
+ file <code class="code">include/debug/debug.h</code>. Preconditions that may or
+ may not be checked, depending on the debug-mode
+ macro <code class="code">_GLIBCXX_DEBUG</code>, are checked via
+ the <code class="code">__requires_xxx</code> macros defined and documented in the
+ same source file. Preconditions are validated using any additional
+ information available at run-time, e.g., the containers that are
+ associated with a particular iterator, the position of the iterator
+ within those containers, the distance between two iterators that may
+ form a valid range, etc. In the absence of suitable information,
+ e.g., an input iterator that is not a safe iterator, these
+ precondition checks will silently succeed.</p><p>The majority of precondition checks use the aforementioned macros,
+ which have the secondary benefit of having prewritten debug
+ messages that use information about the current status of the
+ objects involved (e.g., whether an iterator is singular or what
+ sequence it is attached to) along with some static information
+ (e.g., the names of the function parameters corresponding to the
+ objects involved). When not using these macros, the debug mode uses
+ either the debug-mode assertion
+ macro <code class="code">_GLIBCXX_DEBUG_ASSERT</code> , its pedantic
+ cousin <code class="code">_GLIBCXX_DEBUG_PEDASSERT</code>, or the assertion
+ check macro that supports more advance formulation of error
+ messages, <code class="code">_GLIBCXX_DEBUG_VERIFY</code>. These macros are
+ documented more thoroughly in the debug mode source code.</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.coexistence"></a>Release- and debug-mode coexistence</h4></div></div></div><p>The libstdc++ debug mode is the first debug mode we know of that
+ is able to provide the "Per-use recompilation" (4) guarantee, that
+ allows release-compiled and debug-compiled code to be linked and
+ executed together without causing unpredictable behavior. This
+ guarantee minimizes the recompilation that users are required to
+ perform, shortening the detect-compile-debug bug hunting cycle
+ and making the debug mode easier to incorporate into development
+ environments by minimizing dependencies.</p><p>Achieving link- and run-time coexistence is not a trivial
+ implementation task. To achieve this goal we required a small
+ extension to the GNU C++ compiler (described in the GCC Manual for
+ C++ Extensions, see <a class="ulink" href="http://gcc.gnu.org/onlinedocs/gcc/Strong-Using.html" target="_top">strong
+ using</a>), and a complex organization of debug- and
+ release-modes. The end result is that we have achieved per-use
+ recompilation but have had to give up some checking of the
+ <code class="code">std::basic_string</code> class template (namely, safe
+ iterators).
+</p><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.compile"></a>Compile-time coexistence of release- and debug-mode components</h5></div></div></div><p>Both the release-mode components and the debug-mode
+ components need to exist within a single translation unit so that
+ the debug versions can wrap the release versions. However, only one
+ of these components should be user-visible at any particular
+ time with the standard name, e.g., <code class="code">std::list</code>. </p><p>In release mode, we define only the release-mode version of the
+ component with its standard name and do not include the debugging
+ component at all. The release mode version is defined within the
+ namespace <code class="code">std</code>. Minus the namespace associations, this
+ method leaves the behavior of release mode completely unchanged from
+ its behavior prior to the introduction of the libstdc++ debug
+ mode. Here's an example of what this ends up looking like, in
+ C++.</p><pre class="programlisting">
+namespace std
+{
+ template<typename _Tp, typename _Alloc = allocator<_Tp> >
+ class list
+ {
+ // ...
+ };
+} // namespace std
+</pre><p>In debug mode we include the release-mode container (which is now
+defined in in the namespace <code class="code">__norm</code>) and also the
+debug-mode container. The debug-mode container is defined within the
+namespace <code class="code">__debug</code>, which is associated with namespace
+<code class="code">std</code> via the GNU namespace association extension. This
+method allows the debug and release versions of the same component to
+coexist at compile-time and link-time without causing an unreasonable
+maintenance burden, while minimizing confusion. Again, this boils down
+to C++ code as follows:</p><pre class="programlisting">
+namespace std
+{
+ namespace __norm
+ {
+ template<typename _Tp, typename _Alloc = allocator<_Tp> >
+ class list
+ {
+ // ...
+ };
+ } // namespace __gnu_norm
+
+ namespace __debug
+ {
+ template<typename _Tp, typename _Alloc = allocator<_Tp> >
+ class list
+ : public __norm::list<_Tp, _Alloc>,
+ public __gnu_debug::_Safe_sequence<list<_Tp, _Alloc> >
+ {
+ // ...
+ };
+ } // namespace __norm
+
+ using namespace __debug __attribute__ ((strong));
+}
+</pre></div><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.link"></a>Link- and run-time coexistence of release- and
+ debug-mode components</h5></div></div></div><p>Because each component has a distinct and separate release and
+debug implementation, there are are no issues with link-time
+coexistence: the separate namespaces result in different mangled
+names, and thus unique linkage.</p><p>However, components that are defined and used within the C++
+standard library itself face additional constraints. For instance,
+some of the member functions of <code class="code"> std::moneypunct</code> return
+<code class="code">std::basic_string</code>. Normally, this is not a problem, but
+with a mixed mode standard library that could be using either
+debug-mode or release-mode <code class="code"> basic_string</code> objects, things
+get more complicated. As the return value of a function is not
+encoded into the mangled name, there is no way to specify a
+release-mode or a debug-mode string. In practice, this results in
+runtime errors. A simplified example of this problem is as follows.
+</p><p> Take this translation unit, compiled in debug-mode: </p><pre class="programlisting">
+// -D_GLIBCXX_DEBUG
+#include <string>
+
+std::string test02();
+
+std::string test01()
+{
+ return test02();
+}
+
+int main()
+{
+ test01();
+ return 0;
+}
+</pre><p> ... and linked to this translation unit, compiled in release mode:</p><pre class="programlisting">
+#include <string>
+
+std::string
+test02()
+{
+ return std::string("toast");
+}
+</pre><p> For this reason we cannot easily provide safe iterators for
+ the <code class="code">std::basic_string</code> class template, as it is present
+ throughout the C++ standard library. For instance, locale facets
+ define typedefs that include <code class="code">basic_string</code>: in a mixed
+ debug/release program, should that typedef be based on the
+ debug-mode <code class="code">basic_string</code> or the
+ release-mode <code class="code">basic_string</code>? While the answer could be
+ "both", and the difference hidden via renaming a la the
+ debug/release containers, we must note two things about locale
+ facets:</p><div class="orderedlist"><ol type="1"><li><p>They exist as shared state: one can create a facet in one
+ translation unit and access the facet via the same type name in a
+ different translation unit. This means that we cannot have two
+ different versions of locale facets, because the types would not be
+ the same across debug/release-mode translation unit barriers.</p></li><li><p>They have virtual functions returning strings: these functions
+ mangle in the same way regardless of the mangling of their return
+ types (see above), and their precise signatures can be relied upon
+ by users because they may be overridden in derived classes.</p></li></ol></div><p>With the design of libstdc++ debug mode, we cannot effectively hide
+ the differences between debug and release-mode strings from the
+ user. Failure to hide the differences may result in unpredictable
+ behavior, and for this reason we have opted to only
+ perform <code class="code">basic_string</code> changes that do not require ABI
+ changes. The effect on users is expected to be minimal, as there are
+ simple alternatives (e.g., <code class="code">__gnu_debug::basic_string</code>),
+ and the usability benefit we gain from the ability to mix debug- and
+ release-compiled translation units is enormous.</p></div><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.alt"></a>Alternatives for Coexistence</h5></div></div></div><p>The coexistence scheme above was chosen over many alternatives,
+ including language-only solutions and solutions that also required
+ extensions to the C++ front end. The following is a partial list of
+ solutions, with justifications for our rejection of each.</p><div class="itemizedlist"><ul type="disc"><li><p><span class="emphasis"><em>Completely separate debug/release libraries</em></span>: This is by
+ far the simplest implementation option, where we do not allow any
+ coexistence of debug- and release-compiled translation units in a
+ program. This solution has an extreme negative affect on usability,
+ because it is quite likely that some libraries an application
+ depends on cannot be recompiled easily. This would not meet
+ our <span class="emphasis"><em>usability</em></span> or <span class="emphasis"><em>minimize recompilation</em></span> criteria
+ well.</p></li><li><p><span class="emphasis"><em>Add a <code class="code">Debug</code> boolean template parameter</em></span>:
+ Partial specialization could be used to select the debug
+ implementation when <code class="code">Debug == true</code>, and the state
+ of <code class="code">_GLIBCXX_DEBUG</code> could decide whether the
+ default <code class="code">Debug</code> argument is <code class="code">true</code>
+ or <code class="code">false</code>. This option would break conformance with the
+ C++ standard in both debug <span class="emphasis"><em>and</em></span> release modes. This would
+ not meet our <span class="emphasis"><em>correctness</em></span> criteria. </p></li><li><p><span class="emphasis"><em>Packaging a debug flag in the allocators</em></span>: We could
+ reuse the <code class="code">Allocator</code> template parameter of containers
+ by adding a sentinel wrapper <code class="code">debug<></code> that
+ signals the user's intention to use debugging, and pick up
+ the <code class="code">debug<></code> allocator wrapper in a partial
+ specialization. However, this has two drawbacks: first, there is a
+ conformance issue because the default allocator would not be the
+ standard-specified <code class="code">std::allocator<T></code>. Secondly
+ (and more importantly), users that specify allocators instead of
+ implicitly using the default allocator would not get debugging
+ containers. Thus this solution fails the <span class="emphasis"><em>correctness</em></span>
+ criteria.</p></li><li><p><span class="emphasis"><em>Define debug containers in another namespace, and employ
+ a <code class="code">using</code> declaration (or directive)</em></span>: This is an
+ enticing option, because it would eliminate the need for
+ the <code class="code">link_name</code> extension by aliasing the
+ templates. However, there is no true template aliasing mechanism
+ is C++, because both <code class="code">using</code> directives and using
+ declarations disallow specialization. This method fails
+ the <span class="emphasis"><em>correctness</em></span> criteria.</p></li><li><p><span class="emphasis"><em> Use implementation-specific properties of anonymous
+ namespaces. </em></span>
+ See <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00004.html" target="_top"> this post
+ </a>
+ This method fails the <span class="emphasis"><em>correctness</em></span> criteria.</p></li><li><p><span class="emphasis"><em>Extension: allow reopening on namespaces</em></span>: This would
+ allow the debug mode to effectively alias the
+ namespace <code class="code">std</code> to an internal namespace, such
+ as <code class="code">__gnu_std_debug</code>, so that it is completely
+ separate from the release-mode <code class="code">std</code> namespace. While
+ this will solve some renaming problems and ensure that
+ debug- and release-compiled code cannot be mixed unsafely, it ensures that
+ debug- and release-compiled code cannot be mixed at all. For
+ instance, the program would have two <code class="code">std::cout</code>
+ objects! This solution would fails the <span class="emphasis"><em>minimize
+ recompilation</em></span> requirement, because we would only be able to
+ support option (1) or (2).</p></li><li><p><span class="emphasis"><em>Extension: use link name</em></span>: This option involves
+ complicated re-naming between debug-mode and release-mode
+ components at compile time, and then a g++ extension called <span class="emphasis"><em>
+ link name </em></span> to recover the original names at link time. There
+ are two drawbacks to this approach. One, it's very verbose,
+ relying on macro renaming at compile time and several levels of
+ include ordering. Two, ODR issues remained with container member
+ functions taking no arguments in mixed-mode settings resulting in
+ equivalent link names, <code class="code"> vector::push_back() </code> being
+ one example.
+ See <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00177.html" target="_top">link
+ name</a> </p></li></ul></div><p>Other options may exist for implementing the debug mode, many of
+ which have probably been considered and others that may still be
+ lurking. This list may be expanded over time to include other
+ options that we could have implemented, but in all cases the full
+ ramifications of the approach (as measured against the design goals
+ for a libstdc++ debug mode) should be considered first. The DejaGNU
+ testsuite includes some testcases that check for known problems with
+ some solutions (e.g., the <code class="code">using</code> declaration solution
+ that breaks user specialization), and additional testcases will be
+ added as we are able to identify other typical problem cases. These
+ test cases will serve as a benchmark by which we can compare debug
+ mode implementations.</p></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.debug_mode.design.other"></a>Other Implementations</h3></div></div></div><p>
+ </p><p> There are several existing implementations of debug modes for C++
+ standard library implementations, although none of them directly
+ supports debugging for programs using libstdc++. The existing
+ implementations include:</p><div class="itemizedlist"><ul type="disc"><li><p><a class="ulink" href="http://www.mathcs.sjsu.edu/faculty/horstman/safestl.html" target="_top">SafeSTL</a>:
+ SafeSTL was the original debugging version of the Standard Template
+ Library (STL), implemented by Cay S. Horstmann on top of the
+ Hewlett-Packard STL. Though it inspired much work in this area, it
+ has not been kept up-to-date for use with modern compilers or C++
+ standard library implementations.</p></li><li><p><a class="ulink" href="http://www.stlport.org/" target="_top">STLport</a>: STLport is a free
+ implementation of the C++ standard library derived from the <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">SGI implementation</a>, and
+ ported to many other platforms. It includes a debug mode that uses a
+ wrapper model (that in some way inspired the libstdc++ debug mode
+ design), although at the time of this writing the debug mode is
+ somewhat incomplete and meets only the "Full user recompilation" (2)
+ recompilation guarantee by requiring the user to link against a
+ different library in debug mode vs. release mode.</p></li><li><p><a class="ulink" href="http://www.metrowerks.com/mw/default.htm" target="_top">Metrowerks
+ CodeWarrior</a>: The C++ standard library that ships with Metrowerks
+ CodeWarrior includes a debug mode. It is a full debug-mode
+ implementation (including debugging for CodeWarrior extensions) and
+ is easy to use, although it meets only the "Full recompilation" (1)
+ recompilation guarantee.</p></li></ul></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt12ch30s03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="debug_mode.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="parallel_mode.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Using </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 31. Parallel Mode</td></tr></table></div></body></html>
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