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| <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Backwards Compatibility</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.77.1" /><meta name="keywords" content="ISO C++, backwards" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="appendix_porting.html" title="Appendix B. Porting and Maintenance" /><link rel="prev" href="api.html" title="API Evolution and Deprecation History" /><link rel="next" href="appendix_free.html" title="Appendix C. Free Software Needs Free Documentation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Backwards Compatibility</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="api.html">Prev</a> </td><th width="60%" align="center">Appendix B. |
| Porting and Maintenance |
| |
| </th><td width="20%" align="right"> <a accesskey="n" href="appendix_free.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.appendix.porting.backwards"></a>Backwards Compatibility</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.first"></a>First</h3></div></div></div><p>The first generation GNU C++ library was called libg++. It was a |
| separate GNU project, although reliably paired with GCC. Rumors imply |
| that it had a working relationship with at least two kinds of |
| dinosaur. |
| </p><p>Some background: libg++ was designed and created when there was no |
| ISO standard to provide guidance. Classes like linked lists are now |
| provided for by <code class="classname">list<T></code> and do not need to be |
| created by <code class="function">genclass</code>. (For that matter, templates exist |
| now and are well-supported, whereas genclass (mostly) predates them.) |
| </p><p>There are other classes in libg++ that are not specified in the |
| ISO Standard (e.g., statistical analysis). While there are a lot of |
| really useful things that are used by a lot of people, the Standards |
| Committee couldn't include everything, and so a lot of those |
| <span class="quote">“<span class="quote">obvious</span>”</span> classes didn't get included. |
| </p><p>Known Issues include many of the limitations of its immediate ancestor.</p><p>Portability notes and known implementation limitations are as follows.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.first.ios_base"></a>No <code class="code">ios_base</code></h4></div></div></div><p> At least some older implementations don't have <code class="code">std::ios_base</code>, so you should use <code class="code">std::ios::badbit</code>, <code class="code">std::ios::failbit</code> and <code class="code">std::ios::eofbit</code> and <code class="code">std::ios::goodbit</code>. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.first.cout_cin"></a>No <code class="code">cout</code> in <code class="filename"><ostream.h></code>, no <code class="code">cin</code> in <code class="filename"><istream.h></code></h4></div></div></div><p> |
| In earlier versions of the standard, |
| <code class="filename"><fstream.h></code>, |
| <code class="filename"><ostream.h></code> |
| and <code class="filename"><istream.h></code> |
| used to define |
| <code class="code">cout</code>, <code class="code">cin</code> and so on. ISO C++ specifies that one needs to include |
| <code class="filename"><iostream></code> |
| explicitly to get the required definitions. |
| </p><p> Some include adjustment may be required.</p><p>This project is no longer maintained or supported, and the sources |
| archived. For the desperate, |
| the <a class="link" href="http://gcc.gnu.org/extensions.html" target="_top">GCC extensions |
| page</a> describes where to find the last libg++ source. The code is |
| considered replaced and rewritten. |
| </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.second"></a>Second</h3></div></div></div><p> |
| The second generation GNU C++ library was called libstdc++, or |
| libstdc++-v2. It spans the time between libg++ and pre-ISO C++ |
| standardization and is usually associated with the following GCC |
| releases: egcs 1.x, gcc 2.95, and gcc 2.96. |
| </p><p> |
| The STL portions of this library are based on SGI/HP STL release 3.11. |
| </p><p> |
| This project is no longer maintained or supported, and the sources |
| archived. The code is considered replaced and rewritten. |
| </p><p> |
| Portability notes and known implementation limitations are as follows. |
| </p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.std"></a>Namespace <code class="code">std::</code> not supported</h4></div></div></div><p> |
| Some care is required to support C++ compiler and or library |
| implementation that do not have the standard library in |
| <code class="code">namespace std</code>. |
| </p><p> |
| The following sections list some possible solutions to support compilers |
| that cannot ignore <code class="code">std::</code>-qualified names. |
| </p><p> |
| First, see if the compiler has a flag for this. Namespace |
| back-portability-issues are generally not a problem for g++ |
| compilers that do not have libstdc++ in <code class="code">std::</code>, as the |
| compilers use <code class="option">-fno-honor-std</code> (ignore |
| <code class="code">std::</code>, <code class="code">:: = std::</code>) by default. That is, |
| the responsibility for enabling or disabling <code class="code">std::</code> is |
| on the user; the maintainer does not have to care about it. This |
| probably applies to some other compilers as well. |
| </p><p> |
| Second, experiment with a variety of pre-processor tricks. |
| </p><p> |
| By defining <code class="code">std</code> as a macro, fully-qualified namespace |
| calls become global. Volia. |
| </p><pre class="programlisting"> |
| #ifdef WICKEDLY_OLD_COMPILER |
| # define std |
| #endif |
| </pre><p> |
| Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help. |
| </p><p> |
| Another pre-processor based approach is to define a macro |
| <code class="code">NAMESPACE_STD</code>, which is defined to either |
| <span class="quote">“<span class="quote"> </span>”</span> or <span class="quote">“<span class="quote">std</span>”</span> based on a compile-type |
| test. On GNU systems, this can be done with autotools by means of |
| an autoconf test (see below) for <code class="code">HAVE_NAMESPACE_STD</code>, |
| then using that to set a value for the <code class="code">NAMESPACE_STD</code> |
| macro. At that point, one is able to use |
| <code class="code">NAMESPACE_STD::string</code>, which will evaluate to |
| <code class="code">std::string</code> or <code class="code">::string</code> (i.e., in the |
| global namespace on systems that do not put <code class="code">string</code> in |
| <code class="code">std::</code>). |
| </p><pre class="programlisting"> |
| dnl @synopsis AC_CXX_NAMESPACE_STD |
| dnl |
| dnl If the compiler supports namespace std, define |
| dnl HAVE_NAMESPACE_STD. |
| dnl |
| dnl @category Cxx |
| dnl @author Todd Veldhuizen |
| dnl @author Luc Maisonobe <luc@spaceroots.org> |
| dnl @version 2004-02-04 |
| dnl @license AllPermissive |
| AC_DEFUN([AC_CXX_NAMESPACE_STD], [ |
| AC_CACHE_CHECK(if g++ supports namespace std, |
| ac_cv_cxx_have_std_namespace, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([#include <iostream> |
| std::istream& is = std::cin;],, |
| ac_cv_cxx_have_std_namespace=yes, ac_cv_cxx_have_std_namespace=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_have_std_namespace" = yes; then |
| AC_DEFINE(HAVE_NAMESPACE_STD,,[Define if g++ supports namespace std. ]) |
| fi |
| ]) |
| </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.iterators"></a>Illegal iterator usage</h4></div></div></div><p> |
| The following illustrate implementation-allowed illegal iterator |
| use, and then correct use. |
| </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> |
| you cannot do <code class="code">ostream::operator<<(iterator)</code> |
| to print the address of the iterator => use |
| <code class="code">operator<< &*iterator</code> instead |
| </p></li><li class="listitem"><p> |
| you cannot clear an iterator's reference (<code class="code">iterator = |
| 0</code>) => use <code class="code">iterator = iterator_type();</code> |
| </p></li><li class="listitem"><p> |
| <code class="code">if (iterator)</code> won't work any more => use |
| <code class="code">if (iterator != iterator_type())</code> |
| </p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.isspace"></a><code class="code">isspace</code> from <code class="filename"><cctype></code> is a macro |
| </h4></div></div></div><p> |
| Glibc 2.0.x and 2.1.x define <code class="filename"><ctype.h></code> functionality as macros |
| (isspace, isalpha etc.). |
| </p><p> |
| This implementations of libstdc++, however, keep these functions |
| as macros, and so it is not back-portable to use fully qualified |
| names. For example: |
| </p><pre class="programlisting"> |
| #include <cctype> |
| int main() { std::isspace('X'); } |
| </pre><p> |
| Results in something like this: |
| </p><pre class="programlisting"> |
| std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int) _ISspace ) ; |
| </pre><p> |
| A solution is to modify a header-file so that the compiler tells |
| <code class="filename"><ctype.h></code> to define functions |
| instead of macros: |
| </p><pre class="programlisting"> |
| // This keeps isalnum, et al from being propagated as macros. |
| #if __linux__ |
| # define __NO_CTYPE 1 |
| #endif |
| </pre><p> |
| Then, include <code class="filename"><ctype.h></code> |
| </p><p> |
| Another problem arises if you put a <code class="code">using namespace |
| std;</code> declaration at the top, and include |
| <code class="filename"><ctype.h></code>. This will |
| result in ambiguities between the definitions in the global namespace |
| (<code class="filename"><ctype.h></code>) and the |
| definitions in namespace <code class="code">std::</code> |
| (<code class="code"><cctype></code>). |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.at"></a>No <code class="code">vector::at</code>, <code class="code">deque::at</code>, <code class="code">string::at</code></h4></div></div></div><p> |
| One solution is to add an autoconf-test for this: |
| </p><pre class="programlisting"> |
| AC_MSG_CHECKING(for container::at) |
| AC_TRY_COMPILE( |
| [ |
| #include <vector> |
| #include <deque> |
| #include <string> |
| |
| using namespace std; |
| ], |
| [ |
| deque<int> test_deque(3); |
| test_deque.at(2); |
| vector<int> test_vector(2); |
| test_vector.at(1); |
| string test_string(<span class="quote">“<span class="quote">test_string</span>”</span>); |
| test_string.at(3); |
| ], |
| [AC_MSG_RESULT(yes) |
| AC_DEFINE(HAVE_CONTAINER_AT)], |
| [AC_MSG_RESULT(no)]) |
| </pre><p> |
| If you are using other (non-GNU) compilers it might be a good idea |
| to check for <code class="code">string::at</code> separately. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.eof"></a>No <code class="code">std::char_traits<char>::eof</code></h4></div></div></div><p> |
| Use some kind of autoconf test, plus this: |
| </p><pre class="programlisting"> |
| #ifdef HAVE_CHAR_TRAITS |
| #define CPP_EOF std::char_traits<char>::eof() |
| #else |
| #define CPP_EOF EOF |
| #endif |
| </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.stringclear"></a>No <code class="code">string::clear</code></h4></div></div></div><p> |
| There are two functions for deleting the contents of a string: |
| <code class="code">clear</code> and <code class="code">erase</code> (the latter returns the |
| string). |
| </p><pre class="programlisting"> |
| void |
| clear() { _M_mutate(0, this->size(), 0); } |
| </pre><pre class="programlisting"> |
| basic_string& |
| erase(size_type __pos = 0, size_type __n = npos) |
| { |
| return this->replace(_M_check(__pos), _M_fold(__pos, __n), |
| _M_data(), _M_data()); |
| } |
| </pre><p> |
| Unfortunately, <code class="code">clear</code> is not implemented in this |
| version, so you should use <code class="code">erase</code> (which is probably |
| faster than <code class="code">operator=(charT*)</code>). |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.ostreamform_istreamscan"></a> |
| Removal of <code class="code">ostream::form</code> and <code class="code">istream::scan</code> |
| extensions |
| </h4></div></div></div><p> |
| These are no longer supported. Please use stringstreams instead. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.stringstreams"></a>No <code class="code">basic_stringbuf</code>, <code class="code">basic_stringstream</code></h4></div></div></div><p> |
| Although the ISO standard <code class="code">i/ostringstream</code>-classes are |
| provided, (<code class="filename"><sstream></code>), for |
| compatibility with older implementations the pre-ISO |
| <code class="code">i/ostrstream</code> (<code class="filename"><strstream></code>) interface is also provided, |
| with these caveats: |
| </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> |
| <code class="code">strstream</code> is considered to be deprecated |
| </p></li><li class="listitem"><p> |
| <code class="code">strstream</code> is limited to <code class="code">char</code> |
| </p></li><li class="listitem"><p> |
| with <code class="code">ostringstream</code> you don't have to take care of |
| terminating the string or freeing its memory |
| </p></li><li class="listitem"><p> |
| <code class="code">istringstream</code> can be re-filled (clear(); |
| str(input);) |
| </p></li></ul></div><p> |
| You can then use output-stringstreams like this: |
| </p><pre class="programlisting"> |
| #ifdef HAVE_SSTREAM |
| # include <sstream> |
| #else |
| # include <strstream> |
| #endif |
| |
| #ifdef HAVE_SSTREAM |
| std::ostringstream oss; |
| #else |
| std::ostrstream oss; |
| #endif |
| |
| oss << <span class="quote">“<span class="quote">Name=</span>”</span> << m_name << <span class="quote">“<span class="quote">, number=</span>”</span> << m_number << std::endl; |
| ... |
| #ifndef HAVE_SSTREAM |
| oss << std::ends; // terminate the char*-string |
| #endif |
| |
| // str() returns char* for ostrstream and a string for ostringstream |
| // this also causes ostrstream to think that the buffer's memory |
| // is yours |
| m_label.set_text(oss.str()); |
| #ifndef HAVE_SSTREAM |
| // let the ostrstream take care of freeing the memory |
| oss.freeze(false); |
| #endif |
| </pre><p> |
| Input-stringstreams can be used similarly: |
| </p><pre class="programlisting"> |
| std::string input; |
| ... |
| #ifdef HAVE_SSTREAM |
| std::istringstream iss(input); |
| #else |
| std::istrstream iss(input.c_str()); |
| #endif |
| |
| int i; |
| iss >> i; |
| </pre><p> One (the only?) restriction is that an istrstream cannot be re-filled: |
| </p><pre class="programlisting"> |
| std::istringstream iss(numerator); |
| iss >> m_num; |
| // this is not possible with istrstream |
| iss.clear(); |
| iss.str(denominator); |
| iss >> m_den; |
| </pre><p> |
| If you don't care about speed, you can put these conversions in |
| a template-function: |
| </p><pre class="programlisting"> |
| template <class X> |
| void fromString(const string& input, X& any) |
| { |
| #ifdef HAVE_SSTREAM |
| std::istringstream iss(input); |
| #else |
| std::istrstream iss(input.c_str()); |
| #endif |
| X temp; |
| iss >> temp; |
| if (iss.fail()) |
| throw runtime_error(..) |
| any = temp; |
| } |
| </pre><p> |
| Another example of using stringstreams is in <a class="link" href="strings.html#strings.string.shrink" title="Shrink to Fit">this howto</a>. |
| </p><p> There is additional information in the libstdc++-v2 info files, in |
| particular <span class="quote">“<span class="quote">info iostream</span>”</span>. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.wchar"></a>Little or no wide character support</h4></div></div></div><p> |
| Classes <code class="classname">wstring</code> and |
| <code class="classname">char_traits<wchar_t></code> are |
| not supported. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.iostream_templates"></a>No templatized iostreams</h4></div></div></div><p> |
| Classes <code class="classname">wfilebuf</code> and |
| <code class="classname">wstringstream</code> are not supported. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.thread_safety"></a>Thread safety issues</h4></div></div></div><p> |
| Earlier GCC releases had a somewhat different approach to |
| threading configuration and proper compilation. Before GCC 3.0, |
| configuration of the threading model was dictated by compiler |
| command-line options and macros (both of which were somewhat |
| thread-implementation and port-specific). There were no |
| guarantees related to being able to link code compiled with one |
| set of options and macro setting with another set. |
| </p><p> |
| For GCC 3.0, configuration of the threading model used with |
| libraries and user-code is performed when GCC is configured and |
| built using the --enable-threads and --disable-threads options. |
| The ABI is stable for symbol name-mangling and limited functional |
| compatibility exists between code compiled under different |
| threading models. |
| </p><p> |
| The libstdc++ library has been designed so that it can be used in |
| multithreaded applications (with libstdc++-v2 this was only true |
| of the STL parts.) The first problem is finding a |
| <span class="emphasis"><em>fast</em></span> method of implementation portable to |
| all platforms. Due to historical reasons, some of the library is |
| written against per-CPU-architecture spinlocks and other parts |
| against the gthr.h abstraction layer which is provided by gcc. A |
| minor problem that pops up every so often is different |
| interpretations of what "thread-safe" means for a |
| library (not a general program). We currently use the <a class="link" href="http://www.sgi.com/tech/stl/thread_safety.html" target="_top">same |
| definition that SGI</a> uses for their STL subset. However, |
| the exception for read-only containers only applies to the STL |
| components. This definition is widely-used and something similar |
| will be used in the next version of the C++ standard library. |
| </p><p> |
| Here is a small link farm to threads (no pun) in the mail |
| archives that discuss the threading problem. Each link is to the |
| first relevant message in the thread; from there you can use |
| "Thread Next" to move down the thread. This farm is in |
| latest-to-oldest order. |
| </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> |
| Our threading expert Loren gives a breakdown of <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-10/msg00024.html" target="_top">the |
| six situations involving threads</a> for the 3.0 |
| release series. |
| </p></li><li class="listitem"><p> |
| <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00384.html" target="_top"> |
| This message</a> inspired a recent updating of issues with |
| threading and the SGI STL library. It also contains some |
| example POSIX-multithreaded STL code. |
| </p></li></ul></div><p> |
| (A large selection of links to older messages has been removed; |
| many of the messages from 1999 were lost in a disk crash, and the |
| few people with access to the backup tapes have been too swamped |
| with work to restore them. Many of the points have been |
| superseded anyhow.) |
| </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.third"></a>Third</h3></div></div></div><p> The third generation GNU C++ library is called libstdc++, or |
| libstdc++-v3. |
| </p><p>The subset commonly known as the Standard Template Library |
| (chapters 23 through 25, mostly) is adapted from the final release |
| of the SGI STL (version 3.3), with extensive changes. |
| </p><p>A more formal description of the V3 goals can be found in the |
| official <a class="link" href="source_design_notes.html" title="Design Notes">design document</a>. |
| </p><p>Portability notes and known implementation limitations are as follows.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.headers"></a>Pre-ISO headers moved to backwards or removed</h4></div></div></div><p> The pre-ISO C++ headers |
| (<code class="filename"><iostream.h></code>, |
| <code class="filename"><defalloc.h></code> etc.) are |
| available, unlike previous libstdc++ versions, but inclusion |
| generates a warning that you are using deprecated headers. |
| </p><p>This compatibility layer is constructed by including the |
| standard C++ headers, and injecting any items in |
| <code class="code">std::</code> into the global namespace. |
| </p><p>For those of you new to ISO C++ (welcome, time travelers!), no, |
| that isn't a typo. Yes, the headers really have new names. |
| Marshall Cline's C++ FAQ Lite has a good explanation in <a class="link" href="http://www.parashift.com/c++-faq-lite/coding-standards.html#faq-27.4" target="_top">item |
| [27.4]</a>. |
| </p><p> Some include adjustment may be required. What follows is an |
| autoconf test that defines <code class="code">PRE_STDCXX_HEADERS</code> when they |
| exist.</p><pre class="programlisting"> |
| # AC_HEADER_PRE_STDCXX |
| AC_DEFUN([AC_HEADER_PRE_STDCXX], [ |
| AC_CACHE_CHECK(for pre-ISO C++ include files, |
| ac_cv_cxx_pre_stdcxx, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -Wno-deprecated" |
| |
| # Omit defalloc.h, as compilation with newer compilers is problematic. |
| AC_TRY_COMPILE([ |
| #include <new.h> |
| #include <iterator.h> |
| #include <alloc.h> |
| #include <set.h> |
| #include <hashtable.h> |
| #include <hash_set.h> |
| #include <fstream.h> |
| #include <tempbuf.h> |
| #include <istream.h> |
| #include <bvector.h> |
| #include <stack.h> |
| #include <rope.h> |
| #include <complex.h> |
| #include <ostream.h> |
| #include <heap.h> |
| #include <iostream.h> |
| #include <function.h> |
| #include <multimap.h> |
| #include <pair.h> |
| #include <stream.h> |
| #include <iomanip.h> |
| #include <slist.h> |
| #include <tree.h> |
| #include <vector.h> |
| #include <deque.h> |
| #include <multiset.h> |
| #include <list.h> |
| #include <map.h> |
| #include <algobase.h> |
| #include <hash_map.h> |
| #include <algo.h> |
| #include <queue.h> |
| #include <streambuf.h> |
| ],, |
| ac_cv_cxx_pre_stdcxx=yes, ac_cv_cxx_pre_stdcxx=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_pre_stdcxx" = yes; then |
| AC_DEFINE(PRE_STDCXX_HEADERS,,[Define if pre-ISO C++ header files are present. ]) |
| fi |
| ]) |
| </pre><p>Porting between pre-ISO headers and ISO headers is simple: headers |
| like <code class="filename"><vector.h></code> can be replaced with <code class="filename"><vector></code> and a using |
| directive <code class="code">using namespace std;</code> can be put at the global |
| scope. This should be enough to get this code compiling, assuming the |
| other usage is correct. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.hash"></a>Extension headers hash_map, hash_set moved to ext or backwards</h4></div></div></div><p>At this time most of the features of the SGI STL extension have been |
| replaced by standardized libraries. |
| In particular, the <code class="classname">unordered_map</code> and |
| <code class="classname">unordered_set</code> containers of TR1 and C++ 2011 |
| are suitable replacements for the non-standard |
| <code class="classname">hash_map</code> and <code class="classname">hash_set</code> |
| containers in the SGI STL. |
| </p><p> Header files <code class="filename"><hash_map></code> and <code class="filename"><hash_set></code> moved |
| to <code class="filename"><ext/hash_map></code> and <code class="filename"><ext/hash_set></code>, |
| respectively. At the same time, all types in these files are enclosed |
| in <code class="code">namespace __gnu_cxx</code>. Later versions deprecate |
| these files, and suggest using TR1's <code class="filename"><unordered_map></code> |
| and <code class="filename"><unordered_set></code> instead. |
| </p><p>The extensions are no longer in the global or <code class="code">std</code> |
| namespaces, instead they are declared in the <code class="code">__gnu_cxx</code> |
| namespace. For maximum portability, consider defining a namespace |
| alias to use to talk about extensions, e.g.: |
| </p><pre class="programlisting"> |
| #ifdef __GNUC__ |
| #if __GNUC__ < 3 |
| #include <hash_map.h> |
| namespace extension { using ::hash_map; }; // inherit globals |
| #else |
| #include <backward/hash_map> |
| #if __GNUC__ == 3 && __GNUC_MINOR__ == 0 |
| namespace extension = std; // GCC 3.0 |
| #else |
| namespace extension = ::__gnu_cxx; // GCC 3.1 and later |
| #endif |
| #endif |
| #else // ... there are other compilers, right? |
| namespace extension = std; |
| #endif |
| |
| extension::hash_map<int,int> my_map; |
| </pre><p>This is a bit cleaner than defining typedefs for all the |
| instantiations you might need. |
| </p><p>The following autoconf tests check for working HP/SGI hash containers. |
| </p><pre class="programlisting"> |
| # AC_HEADER_EXT_HASH_MAP |
| AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [ |
| AC_CACHE_CHECK(for ext/hash_map, |
| ac_cv_cxx_ext_hash_map, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -Werror" |
| AC_TRY_COMPILE([#include <ext/hash_map>], [using __gnu_cxx::hash_map;], |
| ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_ext_hash_map" = yes; then |
| AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ]) |
| fi |
| ]) |
| </pre><pre class="programlisting"> |
| # AC_HEADER_EXT_HASH_SET |
| AC_DEFUN([AC_HEADER_EXT_HASH_SET], [ |
| AC_CACHE_CHECK(for ext/hash_set, |
| ac_cv_cxx_ext_hash_set, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -Werror" |
| AC_TRY_COMPILE([#include <ext/hash_set>], [using __gnu_cxx::hash_set;], |
| ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_ext_hash_set" = yes; then |
| AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ]) |
| fi |
| ]) |
| </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.nocreate_noreplace"></a>No <code class="code">ios::nocreate/ios::noreplace</code>. |
| </h4></div></div></div><p> The existence of <code class="code">ios::nocreate</code> being used for |
| input-streams has been confirmed, most probably because the author |
| thought it would be more correct to specify nocreate explicitly. So |
| it can be left out for input-streams. |
| </p><p>For output streams, <span class="quote">“<span class="quote">nocreate</span>”</span> is probably the default, |
| unless you specify <code class="code">std::ios::trunc</code> ? To be safe, you can |
| open the file for reading, check if it has been opened, and then |
| decide whether you want to create/replace or not. To my knowledge, |
| even older implementations support <code class="code">app</code>, <code class="code">ate</code> |
| and <code class="code">trunc</code> (except for <code class="code">app</code> ?). |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.streamattach"></a> |
| No <code class="code">stream::attach(int fd)</code> |
| </h4></div></div></div><p> |
| Phil Edwards writes: It was considered and rejected for the ISO |
| standard. Not all environments use file descriptors. Of those |
| that do, not all of them use integers to represent them. |
| </p><p> |
| For a portable solution (among systems which use |
| file descriptors), you need to implement a subclass of |
| <code class="code">std::streambuf</code> (or |
| <code class="code">std::basic_streambuf<..></code>) which opens a file |
| given a descriptor, and then pass an instance of this to the |
| stream-constructor. |
| </p><p> |
| An extension is available that implements this. |
| <code class="filename"><ext/stdio_filebuf.h></code> contains a derived class called |
| <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00074.html" target="_top"><code class="code">__gnu_cxx::stdio_filebuf</code></a>. |
| This class can be constructed from a C <code class="code">FILE*</code> or a file |
| descriptor, and provides the <code class="code">fd()</code> function. |
| </p><p> |
| For another example of this, refer to |
| <a class="link" href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a> |
| by Nicolai Josuttis. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx98"></a> |
| Support for C++98 dialect. |
| </h4></div></div></div><p>Check for complete library coverage of the C++1998/2003 standard. |
| </p><pre class="programlisting"> |
| # AC_HEADER_STDCXX_98 |
| AC_DEFUN([AC_HEADER_STDCXX_98], [ |
| AC_CACHE_CHECK(for ISO C++ 98 include files, |
| ac_cv_cxx_stdcxx_98, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([ |
| #include <cassert> |
| #include <cctype> |
| #include <cerrno> |
| #include <cfloat> |
| #include <ciso646> |
| #include <climits> |
| #include <clocale> |
| #include <cmath> |
| #include <csetjmp> |
| #include <csignal> |
| #include <cstdarg> |
| #include <cstddef> |
| #include <cstdio> |
| #include <cstdlib> |
| #include <cstring> |
| #include <ctime> |
| |
| #include <algorithm> |
| #include <bitset> |
| #include <complex> |
| #include <deque> |
| #include <exception> |
| #include <fstream> |
| #include <functional> |
| #include <iomanip> |
| #include <ios> |
| #include <iosfwd> |
| #include <iostream> |
| #include <istream> |
| #include <iterator> |
| #include <limits> |
| #include <list> |
| #include <locale> |
| #include <map> |
| #include <memory> |
| #include <new> |
| #include <numeric> |
| #include <ostream> |
| #include <queue> |
| #include <set> |
| #include <sstream> |
| #include <stack> |
| #include <stdexcept> |
| #include <streambuf> |
| #include <string> |
| #include <typeinfo> |
| #include <utility> |
| #include <valarray> |
| #include <vector> |
| ],, |
| ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_stdcxx_98" = yes; then |
| AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ]) |
| fi |
| ]) |
| </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_tr1"></a> |
| Support for C++TR1 dialect. |
| </h4></div></div></div><p>Check for library coverage of the TR1 standard. |
| </p><pre class="programlisting"> |
| # AC_HEADER_STDCXX_TR1 |
| AC_DEFUN([AC_HEADER_STDCXX_TR1], [ |
| AC_CACHE_CHECK(for ISO C++ TR1 include files, |
| ac_cv_cxx_stdcxx_tr1, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([ |
| #include <tr1/array> |
| #include <tr1/ccomplex> |
| #include <tr1/cctype> |
| #include <tr1/cfenv> |
| #include <tr1/cfloat> |
| #include <tr1/cinttypes> |
| #include <tr1/climits> |
| #include <tr1/cmath> |
| #include <tr1/complex> |
| #include <tr1/cstdarg> |
| #include <tr1/cstdbool> |
| #include <tr1/cstdint> |
| #include <tr1/cstdio> |
| #include <tr1/cstdlib> |
| #include <tr1/ctgmath> |
| #include <tr1/ctime> |
| #include <tr1/cwchar> |
| #include <tr1/cwctype> |
| #include <tr1/functional> |
| #include <tr1/memory> |
| #include <tr1/random> |
| #include <tr1/regex> |
| #include <tr1/tuple> |
| #include <tr1/type_traits> |
| #include <tr1/unordered_set> |
| #include <tr1/unordered_map> |
| #include <tr1/utility> |
| ],, |
| ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_stdcxx_tr1" = yes; then |
| AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ]) |
| fi |
| ]) |
| </pre><p>An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>. |
| </p><pre class="programlisting"> |
| # AC_HEADER_TR1_UNORDERED_MAP |
| AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [ |
| AC_CACHE_CHECK(for tr1/unordered_map, |
| ac_cv_cxx_tr1_unordered_map, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;], |
| ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_tr1_unordered_map" = yes; then |
| AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ]) |
| fi |
| ]) |
| </pre><pre class="programlisting"> |
| # AC_HEADER_TR1_UNORDERED_SET |
| AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [ |
| AC_CACHE_CHECK(for tr1/unordered_set, |
| ac_cv_cxx_tr1_unordered_set, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([#include <tr1/unordered_set>], [using std::tr1::unordered_set;], |
| ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no) |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_tr1_unordered_set" = yes; then |
| AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ]) |
| fi |
| ]) |
| </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx11"></a> |
| Support for C++11 dialect. |
| </h4></div></div></div><p>Check for baseline language coverage in the compiler for the C++11 standard. |
| </p><pre class="programlisting"> |
| # AC_COMPILE_STDCXX_11 |
| AC_DEFUN([AC_COMPILE_STDCXX_11], [ |
| AC_CACHE_CHECK(if g++ supports C++11 features without additional flags, |
| ac_cv_cxx_compile_cxx11_native, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| AC_TRY_COMPILE([ |
| template <typename T> |
| struct check final |
| { |
| static constexpr T value{ __cplusplus }; |
| }; |
| |
| typedef check<check<bool>> right_angle_brackets; |
| |
| int a; |
| decltype(a) b; |
| |
| typedef check<int> check_type; |
| check_type c{}; |
| check_type&& cr = static_cast<check_type&&>(c); |
| |
| static_assert(check_type::value == 201103L, "C++11 compiler");],, |
| ac_cv_cxx_compile_cxx11_native=yes, ac_cv_cxx_compile_cxx11_native=no) |
| AC_LANG_RESTORE |
| ]) |
| |
| AC_CACHE_CHECK(if g++ supports C++11 features with -std=c++11, |
| ac_cv_cxx_compile_cxx11_cxx, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=c++11" |
| AC_TRY_COMPILE([ |
| template <typename T> |
| struct check final |
| { |
| static constexpr T value{ __cplusplus }; |
| }; |
| |
| typedef check<check<bool>> right_angle_brackets; |
| |
| int a; |
| decltype(a) b; |
| |
| typedef check<int> check_type; |
| check_type c{}; |
| check_type&& cr = static_cast<check_type&&>(c); |
| |
| static_assert(check_type::value == 201103L, "C++11 compiler");],, |
| ac_cv_cxx_compile_cxx11_cxx=yes, ac_cv_cxx_compile_cxx11_cxx=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| |
| AC_CACHE_CHECK(if g++ supports C++11 features with -std=gnu++11, |
| ac_cv_cxx_compile_cxx11_gxx, |
| [AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| AC_TRY_COMPILE([ |
| template <typename T> |
| struct check final |
| { |
| static constexpr T value{ __cplusplus }; |
| }; |
| |
| typedef check<check<bool>> right_angle_brackets; |
| |
| int a; |
| decltype(a) b; |
| |
| typedef check<int> check_type; |
| check_type c{}; |
| check_type&& cr = static_cast<check_type&&>(c); |
| |
| static_assert(check_type::value == 201103L, "C++11 compiler");],, |
| ac_cv_cxx_compile_cxx11_gxx=yes, ac_cv_cxx_compile_cxx11_gxx=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| |
| if test "$ac_cv_cxx_compile_cxx11_native" = yes || |
| test "$ac_cv_cxx_compile_cxx11_cxx" = yes || |
| test "$ac_cv_cxx_compile_cxx11_gxx" = yes; then |
| AC_DEFINE(HAVE_STDCXX_11,,[Define if g++ supports C++11 features. ]) |
| fi |
| ]) |
| </pre><p>Check for library coverage of the C++2011 standard. |
| (Some library headers are commented out in this check, they are |
| not currently provided by libstdc++). |
| </p><pre class="programlisting"> |
| # AC_HEADER_STDCXX_11 |
| AC_DEFUN([AC_HEADER_STDCXX_11], [ |
| AC_CACHE_CHECK(for ISO C++11 include files, |
| ac_cv_cxx_stdcxx_11, |
| [AC_REQUIRE([AC_COMPILE_STDCXX_11]) |
| AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| |
| AC_TRY_COMPILE([ |
| #include <cassert> |
| #include <ccomplex> |
| #include <cctype> |
| #include <cerrno> |
| #include <cfenv> |
| #include <cfloat> |
| #include <cinttypes> |
| #include <ciso646> |
| #include <climits> |
| #include <clocale> |
| #include <cmath> |
| #include <csetjmp> |
| #include <csignal> |
| #include <cstdalign> |
| #include <cstdarg> |
| #include <cstdbool> |
| #include <cstddef> |
| #include <cstdint> |
| #include <cstdio> |
| #include <cstdlib> |
| #include <cstring> |
| #include <ctgmath> |
| #include <ctime> |
| // #include <cuchar> |
| #include <cwchar> |
| #include <cwctype> |
| |
| #include <algorithm> |
| #include <array> |
| #include <atomic> |
| #include <bitset> |
| #include <chrono> |
| // #include <codecvt> |
| #include <complex> |
| #include <condition_variable> |
| #include <deque> |
| #include <exception> |
| #include <forward_list> |
| #include <fstream> |
| #include <functional> |
| #include <future> |
| #include <initializer_list> |
| #include <iomanip> |
| #include <ios> |
| #include <iosfwd> |
| #include <iostream> |
| #include <istream> |
| #include <iterator> |
| #include <limits> |
| #include <list> |
| #include <locale> |
| #include <map> |
| #include <memory> |
| #include <mutex> |
| #include <new> |
| #include <numeric> |
| #include <ostream> |
| #include <queue> |
| #include <random> |
| #include <ratio> |
| #include <regex> |
| #include <scoped_allocator> |
| #include <set> |
| #include <sstream> |
| #include <stack> |
| #include <stdexcept> |
| #include <streambuf> |
| #include <string> |
| #include <system_error> |
| #include <thread> |
| #include <tuple> |
| #include <typeindex> |
| #include <typeinfo> |
| #include <type_traits> |
| #include <unordered_map> |
| #include <unordered_set> |
| #include <utility> |
| #include <valarray> |
| #include <vector> |
| ],, |
| ac_cv_cxx_stdcxx_11=yes, ac_cv_cxx_stdcxx_11=no) |
| AC_LANG_RESTORE |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| ]) |
| if test "$ac_cv_cxx_stdcxx_11" = yes; then |
| AC_DEFINE(STDCXX_11_HEADERS,,[Define if ISO C++11 header files are present. ]) |
| fi |
| ]) |
| </pre><p>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For |
| <code class="filename"><unordered_map></code> |
| </p><pre class="programlisting"> |
| # AC_HEADER_UNORDERED_MAP |
| AC_DEFUN([AC_HEADER_UNORDERED_MAP], [ |
| AC_CACHE_CHECK(for unordered_map, |
| ac_cv_cxx_unordered_map, |
| [AC_REQUIRE([AC_COMPILE_STDCXX_11]) |
| AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| AC_TRY_COMPILE([#include <unordered_map>], [using std::unordered_map;], |
| ac_cv_cxx_unordered_map=yes, ac_cv_cxx_unordered_map=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_unordered_map" = yes; then |
| AC_DEFINE(HAVE_UNORDERED_MAP,,[Define if unordered_map is present. ]) |
| fi |
| ]) |
| </pre><pre class="programlisting"> |
| # AC_HEADER_UNORDERED_SET |
| AC_DEFUN([AC_HEADER_UNORDERED_SET], [ |
| AC_CACHE_CHECK(for unordered_set, |
| ac_cv_cxx_unordered_set, |
| [AC_REQUIRE([AC_COMPILE_STDCXX_11]) |
| AC_LANG_SAVE |
| AC_LANG_CPLUSPLUS |
| ac_save_CXXFLAGS="$CXXFLAGS" |
| CXXFLAGS="$CXXFLAGS -std=gnu++11" |
| AC_TRY_COMPILE([#include <unordered_set>], [using std::unordered_set;], |
| ac_cv_cxx_unordered_set=yes, ac_cv_cxx_unordered_set=no) |
| CXXFLAGS="$ac_save_CXXFLAGS" |
| AC_LANG_RESTORE |
| ]) |
| if test "$ac_cv_cxx_unordered_set" = yes; then |
| AC_DEFINE(HAVE_UNORDERED_SET,,[Define if unordered_set is present. ]) |
| fi |
| ]) |
| </pre><p> |
| Some C++11 features first appeared in GCC 4.3 and could be enabled by |
| <code class="option">-std=c++0x</code> and <code class="option">-std=gnu++0x</code> for GCC |
| releases which pre-date the 2011 standard. Those C++11 features and GCC's |
| support for them were still changing until the 2011 standard was finished, |
| but the autoconf checks above could be extended to test for incomplete |
| C++11 support with <code class="option">-std=c++0x</code> and |
| <code class="option">-std=gnu++0x</code>. |
| </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.iterator_type"></a> |
| <code class="code">Container::iterator_type</code> is not necessarily <code class="code">Container::value_type*</code> |
| </h4></div></div></div><p> |
| This is a change in behavior from older versions. Now, most |
| <span class="type">iterator_type</span> typedefs in container classes are POD |
| objects, not <span class="type">value_type</span> pointers. |
| </p></div></div><div class="bibliography"><div class="titlepage"><div><div><h3 class="title"><a id="backwards.biblio"></a>Bibliography</h3></div></div></div><div class="biblioentry"><a id="idp23415104"></a><p><span class="title"><em> |
| <a class="link" href="http://www.kegel.com/gcc/gcc4.html" target="_top"> |
| Migrating to GCC 4.1 |
| </a> |
| </em>. </span><span class="author"><span class="firstname">Dan</span> <span class="surname">Kegel</span>. </span></p></div><div class="biblioentry"><a id="idp23417888"></a><p><span class="title"><em> |
| <a class="link" href="http://lists.debian.org/debian-gcc/2006/03/msg00405.html" target="_top"> |
| Building the Whole Debian Archive with GCC 4.1: A Summary |
| </a> |
| </em>. </span><span class="author"><span class="firstname">Martin</span> <span class="surname">Michlmayr</span>. </span></p></div><div class="biblioentry"><a id="idp23420736"></a><p><span class="title"><em> |
| <a class="link" href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html" target="_top"> |
| Migration guide for GCC-3.2 |
| </a> |
| </em>. </span></p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="api.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendix_porting.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="appendix_free.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">API Evolution and Deprecation History </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Appendix C. |
| Free Software Needs Free Documentation |
| |
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