1<?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"><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 V1.78.1" /><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.�� 3 Porting and Maintenance 4 5</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 6separate GNU project, although reliably paired with GCC. Rumors imply 7that it had a working relationship with at least two kinds of 8dinosaur. 9</p><p>Some background: libg++ was designed and created when there was no 10ISO standard to provide guidance. Classes like linked lists are now 11provided for by <code class="classname">list<T></code> and do not need to be 12created by <code class="function">genclass</code>. (For that matter, templates exist 13now and are well-supported, whereas genclass (mostly) predates them.) 14</p><p>There are other classes in libg++ that are not specified in the 15ISO Standard (e.g., statistical analysis). While there are a lot of 16really useful things that are used by a lot of people, the Standards 17Committee couldn't include everything, and so a lot of those 18<span class="quote">���<span class="quote">obvious</span>���</span> classes didn't get included. 19</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>. 20</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> 21 In earlier versions of the standard, 22 <code class="filename"><fstream.h></code>, 23 <code class="filename"><ostream.h></code> 24 and <code class="filename"><istream.h></code> 25 used to define 26 <code class="code">cout</code>, <code class="code">cin</code> and so on. ISO C++ specifies that one needs to include 27 <code class="filename"><iostream></code> 28 explicitly to get the required definitions. 29 </p><p> Some include adjustment may be required.</p><p>This project is no longer maintained or supported, and the sources 30archived. For the desperate, 31the <a class="link" href="http://gcc.gnu.org/extensions.html" target="_top">GCC extensions 32page</a> describes where to find the last libg++ source. The code is 33considered replaced and rewritten. 34</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> 35 The second generation GNU C++ library was called libstdc++, or 36 libstdc++-v2. It spans the time between libg++ and pre-ISO C++ 37 standardization and is usually associated with the following GCC 38 releases: egcs 1.x, gcc 2.95, and gcc 2.96. 39</p><p> 40 The STL portions of this library are based on SGI/HP STL release 3.11. 41</p><p> 42 This project is no longer maintained or supported, and the sources 43 archived. The code is considered replaced and rewritten. 44</p><p> 45 Portability notes and known implementation limitations are as follows. 46</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> 47 Some care is required to support C++ compiler and or library 48 implementation that do not have the standard library in 49 <code class="code">namespace std</code>. 50 </p><p> 51 The following sections list some possible solutions to support compilers 52 that cannot ignore <code class="code">std::</code>-qualified names. 53 </p><p> 54 First, see if the compiler has a flag for this. Namespace 55 back-portability-issues are generally not a problem for g++ 56 compilers that do not have libstdc++ in <code class="code">std::</code>, as the 57 compilers use <code class="option">-fno-honor-std</code> (ignore 58 <code class="code">std::</code>, <code class="code">:: = std::</code>) by default. That is, 59 the responsibility for enabling or disabling <code class="code">std::</code> is 60 on the user; the maintainer does not have to care about it. This 61 probably applies to some other compilers as well. 62 </p><p> 63 Second, experiment with a variety of pre-processor tricks. 64 </p><p> 65 By defining <code class="code">std</code> as a macro, fully-qualified namespace 66 calls become global. Volia. 67 </p><pre class="programlisting"> 68#ifdef WICKEDLY_OLD_COMPILER 69# define std 70#endif 71</pre><p> 72 Thanks to Juergen Heinzl who posted this solution on gnu.gcc.help. 73 </p><p> 74 Another pre-processor based approach is to define a macro 75 <code class="code">NAMESPACE_STD</code>, which is defined to either 76 <span class="quote">���<span class="quote"> </span>���</span> or <span class="quote">���<span class="quote">std</span>���</span> based on a compile-type 77 test. On GNU systems, this can be done with autotools by means of 78 an autoconf test (see below) for <code class="code">HAVE_NAMESPACE_STD</code>, 79 then using that to set a value for the <code class="code">NAMESPACE_STD</code> 80 macro. At that point, one is able to use 81 <code class="code">NAMESPACE_STD::string</code>, which will evaluate to 82 <code class="code">std::string</code> or <code class="code">::string</code> (i.e., in the 83 global namespace on systems that do not put <code class="code">string</code> in 84 <code class="code">std::</code>). 85 </p><pre class="programlisting"> 86dnl @synopsis AC_CXX_NAMESPACE_STD 87dnl 88dnl If the compiler supports namespace std, define 89dnl HAVE_NAMESPACE_STD. 90dnl 91dnl @category Cxx 92dnl @author Todd Veldhuizen 93dnl @author Luc Maisonobe <luc@spaceroots.org> 94dnl @version 2004-02-04 95dnl @license AllPermissive 96AC_DEFUN([AC_CXX_NAMESPACE_STD], [ 97 AC_CACHE_CHECK(if g++ supports namespace std, 98 ac_cv_cxx_have_std_namespace, 99 [AC_LANG_SAVE 100 AC_LANG_CPLUSPLUS 101 AC_TRY_COMPILE([#include <iostream> 102 std::istream& is = std::cin;],, 103 ac_cv_cxx_have_std_namespace=yes, ac_cv_cxx_have_std_namespace=no) 104 AC_LANG_RESTORE 105 ]) 106 if test "$ac_cv_cxx_have_std_namespace" = yes; then 107 AC_DEFINE(HAVE_NAMESPACE_STD,,[Define if g++ supports namespace std. ]) 108 fi 109]) 110</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> 111 The following illustrate implementation-allowed illegal iterator 112 use, and then correct use. 113</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> 114 you cannot do <code class="code">ostream::operator<<(iterator)</code> 115 to print the address of the iterator => use 116 <code class="code">operator<< &*iterator</code> instead 117 </p></li><li class="listitem"><p> 118 you cannot clear an iterator's reference (<code class="code">iterator = 119 0</code>) => use <code class="code">iterator = iterator_type();</code> 120 </p></li><li class="listitem"><p> 121 <code class="code">if (iterator)</code> won't work any more => use 122 <code class="code">if (iterator != iterator_type())</code> 123 </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 124 </h4></div></div></div><p> 125 Glibc 2.0.x and 2.1.x define <code class="filename"><ctype.h></code> functionality as macros 126 (isspace, isalpha etc.). 127 </p><p> 128 This implementations of libstdc++, however, keep these functions 129 as macros, and so it is not back-portable to use fully qualified 130 names. For example: 131 </p><pre class="programlisting"> 132#include <cctype> 133int main() { std::isspace('X'); } 134</pre><p> 135 Results in something like this: 136</p><pre class="programlisting"> 137std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int) _ISspace ) ; 138</pre><p> 139 A solution is to modify a header-file so that the compiler tells 140 <code class="filename"><ctype.h></code> to define functions 141 instead of macros: 142</p><pre class="programlisting"> 143// This keeps isalnum, et al from being propagated as macros. 144#if __linux__ 145# define __NO_CTYPE 1 146#endif 147</pre><p> 148 Then, include <code class="filename"><ctype.h></code> 149</p><p> 150 Another problem arises if you put a <code class="code">using namespace 151 std;</code> declaration at the top, and include 152 <code class="filename"><ctype.h></code>. This will 153 result in ambiguities between the definitions in the global namespace 154 (<code class="filename"><ctype.h></code>) and the 155 definitions in namespace <code class="code">std::</code> 156 (<code class="code"><cctype></code>). 157</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> 158 One solution is to add an autoconf-test for this: 159</p><pre class="programlisting"> 160AC_MSG_CHECKING(for container::at) 161AC_TRY_COMPILE( 162[ 163#include <vector> 164#include <deque> 165#include <string> 166 167using namespace std; 168], 169[ 170deque<int> test_deque(3); 171test_deque.at(2); 172vector<int> test_vector(2); 173test_vector.at(1); 174string test_string(<span class="quote">���<span class="quote">test_string</span>���</span>); 175test_string.at(3); 176], 177[AC_MSG_RESULT(yes) 178AC_DEFINE(HAVE_CONTAINER_AT)], 179[AC_MSG_RESULT(no)]) 180</pre><p> 181 If you are using other (non-GNU) compilers it might be a good idea 182 to check for <code class="code">string::at</code> separately. 183</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> 184 Use some kind of autoconf test, plus this: 185</p><pre class="programlisting"> 186#ifdef HAVE_CHAR_TRAITS 187#define CPP_EOF std::char_traits<char>::eof() 188#else 189#define CPP_EOF EOF 190#endif 191</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> 192 There are two functions for deleting the contents of a string: 193 <code class="code">clear</code> and <code class="code">erase</code> (the latter returns the 194 string). 195</p><pre class="programlisting"> 196void 197clear() { _M_mutate(0, this->size(), 0); } 198</pre><pre class="programlisting"> 199basic_string& 200erase(size_type __pos = 0, size_type __n = npos) 201{ 202 return this->replace(_M_check(__pos), _M_fold(__pos, __n), 203 _M_data(), _M_data()); 204} 205</pre><p> 206 Unfortunately, <code class="code">clear</code> is not implemented in this 207 version, so you should use <code class="code">erase</code> (which is probably 208 faster than <code class="code">operator=(charT*)</code>). 209</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.second.ostreamform_istreamscan"></a> 210 Removal of <code class="code">ostream::form</code> and <code class="code">istream::scan</code> 211 extensions 212</h4></div></div></div><p> 213 These are no longer supported. Please use stringstreams instead. 214</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> 215 Although the ISO standard <code class="code">i/ostringstream</code>-classes are 216 provided, (<code class="filename"><sstream></code>), for 217 compatibility with older implementations the pre-ISO 218 <code class="code">i/ostrstream</code> (<code class="filename"><strstream></code>) interface is also provided, 219 with these caveats: 220</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> 221 <code class="code">strstream</code> is considered to be deprecated 222 </p></li><li class="listitem"><p> 223 <code class="code">strstream</code> is limited to <code class="code">char</code> 224 </p></li><li class="listitem"><p> 225 with <code class="code">ostringstream</code> you don't have to take care of 226 terminating the string or freeing its memory 227 </p></li><li class="listitem"><p> 228 <code class="code">istringstream</code> can be re-filled (clear(); 229 str(input);) 230 </p></li></ul></div><p> 231 You can then use output-stringstreams like this: 232</p><pre class="programlisting"> 233#ifdef HAVE_SSTREAM 234# include <sstream> 235#else 236# include <strstream> 237#endif 238 239#ifdef HAVE_SSTREAM 240 std::ostringstream oss; 241#else 242 std::ostrstream oss; 243#endif 244 245oss << "Name=" << m_name << ", number=" << m_number << std::endl; 246... 247#ifndef HAVE_SSTREAM 248 oss << std::ends; // terminate the char*-string 249#endif 250 251// str() returns char* for ostrstream and a string for ostringstream 252// this also causes ostrstream to think that the buffer's memory 253// is yours 254m_label.set_text(oss.str()); 255#ifndef HAVE_SSTREAM 256 // let the ostrstream take care of freeing the memory 257 oss.freeze(false); 258#endif 259</pre><p> 260 Input-stringstreams can be used similarly: 261</p><pre class="programlisting"> 262std::string input; 263... 264#ifdef HAVE_SSTREAM 265std::istringstream iss(input); 266#else 267std::istrstream iss(input.c_str()); 268#endif 269 270int i; 271iss >> i; 272</pre><p> One (the only?) restriction is that an istrstream cannot be re-filled: 273</p><pre class="programlisting"> 274std::istringstream iss(numerator); 275iss >> m_num; 276// this is not possible with istrstream 277iss.clear(); 278iss.str(denominator); 279iss >> m_den; 280</pre><p> 281If you don't care about speed, you can put these conversions in 282 a template-function: 283</p><pre class="programlisting"> 284template <class X> 285void fromString(const string& input, X& any) 286{ 287#ifdef HAVE_SSTREAM 288std::istringstream iss(input); 289#else 290std::istrstream iss(input.c_str()); 291#endif 292X temp; 293iss >> temp; 294if (iss.fail()) 295throw runtime_error(..) 296any = temp; 297} 298</pre><p> 299 Another example of using stringstreams is in <a class="link" href="strings.html#strings.string.shrink" title="Shrink to Fit">this howto</a>. 300</p><p> There is additional information in the libstdc++-v2 info files, in 301particular <span class="quote">���<span class="quote">info iostream</span>���</span>. 302</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> 303 Classes <code class="classname">wstring</code> and 304 <code class="classname">char_traits<wchar_t></code> are 305 not supported. 306 </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> 307 Classes <code class="classname">wfilebuf</code> and 308 <code class="classname">wstringstream</code> are not supported. 309 </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> 310 Earlier GCC releases had a somewhat different approach to 311 threading configuration and proper compilation. Before GCC 3.0, 312 configuration of the threading model was dictated by compiler 313 command-line options and macros (both of which were somewhat 314 thread-implementation and port-specific). There were no 315 guarantees related to being able to link code compiled with one 316 set of options and macro setting with another set. 317 </p><p> 318 For GCC 3.0, configuration of the threading model used with 319 libraries and user-code is performed when GCC is configured and 320 built using the --enable-threads and --disable-threads options. 321 The ABI is stable for symbol name-mangling and limited functional 322 compatibility exists between code compiled under different 323 threading models. 324 </p><p> 325 The libstdc++ library has been designed so that it can be used in 326 multithreaded applications (with libstdc++-v2 this was only true 327 of the STL parts.) The first problem is finding a 328 <span class="emphasis"><em>fast</em></span> method of implementation portable to 329 all platforms. Due to historical reasons, some of the library is 330 written against per-CPU-architecture spinlocks and other parts 331 against the gthr.h abstraction layer which is provided by gcc. A 332 minor problem that pops up every so often is different 333 interpretations of what "thread-safe" means for a 334 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 335 definition that SGI</a> uses for their STL subset. However, 336 the exception for read-only containers only applies to the STL 337 components. This definition is widely-used and something similar 338 will be used in the next version of the C++ standard library. 339 </p><p> 340 Here is a small link farm to threads (no pun) in the mail 341 archives that discuss the threading problem. Each link is to the 342 first relevant message in the thread; from there you can use 343 "Thread Next" to move down the thread. This farm is in 344 latest-to-oldest order. 345 </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> 346 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 347 six situations involving threads</a> for the 3.0 348 release series. 349 </p></li><li class="listitem"><p> 350 <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00384.html" target="_top"> 351 This message</a> inspired a recent updating of issues with 352 threading and the SGI STL library. It also contains some 353 example POSIX-multithreaded STL code. 354 </p></li></ul></div><p> 355 (A large selection of links to older messages has been removed; 356 many of the messages from 1999 were lost in a disk crash, and the 357 few people with access to the backup tapes have been too swamped 358 with work to restore them. Many of the points have been 359 superseded anyhow.) 360 </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 361libstdc++-v3. 362</p><p>The subset commonly known as the Standard Template Library 363 (clauses 23 through 25, mostly) is adapted from the final release 364 of the SGI STL (version 3.3), with extensive changes. 365 </p><p>A more formal description of the V3 goals can be found in the 366 official <a class="link" href="source_design_notes.html" title="Design Notes">design document</a>. 367 </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 368 (<code class="filename"><iostream.h></code>, 369 <code class="filename"><defalloc.h></code> etc.) are 370 available, unlike previous libstdc++ versions, but inclusion 371 generates a warning that you are using deprecated headers. 372</p><p>This compatibility layer is constructed by including the 373 standard C++ headers, and injecting any items in 374 <code class="code">std::</code> into the global namespace. 375 </p><p>For those of you new to ISO C++ (welcome, time travelers!), no, 376 that isn't a typo. Yes, the headers really have new names. 377 Marshall Cline's C++ FAQ Lite has a good explanation in <a class="link" href="http://www.parashift.com/c++-faq-lite/std-headers.html" target="_top">What's 378 the difference between <xxx> and <xxx.h> headers?</a>. 379 </p><p> Some include adjustment may be required. What follows is an 380autoconf test that defines <code class="code">PRE_STDCXX_HEADERS</code> when they 381exist.</p><pre class="programlisting"> 382# AC_HEADER_PRE_STDCXX 383AC_DEFUN([AC_HEADER_PRE_STDCXX], [ 384 AC_CACHE_CHECK(for pre-ISO C++ include files, 385 ac_cv_cxx_pre_stdcxx, 386 [AC_LANG_SAVE 387 AC_LANG_CPLUSPLUS 388 ac_save_CXXFLAGS="$CXXFLAGS" 389 CXXFLAGS="$CXXFLAGS -Wno-deprecated" 390 391 # Omit defalloc.h, as compilation with newer compilers is problematic. 392 AC_TRY_COMPILE([ 393 #include <new.h> 394 #include <iterator.h> 395 #include <alloc.h> 396 #include <set.h> 397 #include <hashtable.h> 398 #include <hash_set.h> 399 #include <fstream.h> 400 #include <tempbuf.h> 401 #include <istream.h> 402 #include <bvector.h> 403 #include <stack.h> 404 #include <rope.h> 405 #include <complex.h> 406 #include <ostream.h> 407 #include <heap.h> 408 #include <iostream.h> 409 #include <function.h> 410 #include <multimap.h> 411 #include <pair.h> 412 #include <stream.h> 413 #include <iomanip.h> 414 #include <slist.h> 415 #include <tree.h> 416 #include <vector.h> 417 #include <deque.h> 418 #include <multiset.h> 419 #include <list.h> 420 #include <map.h> 421 #include <algobase.h> 422 #include <hash_map.h> 423 #include <algo.h> 424 #include <queue.h> 425 #include <streambuf.h> 426 ],, 427 ac_cv_cxx_pre_stdcxx=yes, ac_cv_cxx_pre_stdcxx=no) 428 CXXFLAGS="$ac_save_CXXFLAGS" 429 AC_LANG_RESTORE 430 ]) 431 if test "$ac_cv_cxx_pre_stdcxx" = yes; then 432 AC_DEFINE(PRE_STDCXX_HEADERS,,[Define if pre-ISO C++ header files are present. ]) 433 fi 434]) 435</pre><p>Porting between pre-ISO headers and ISO headers is simple: headers 436like <code class="filename"><vector.h></code> can be replaced with <code class="filename"><vector></code> and a using 437directive <code class="code">using namespace std;</code> can be put at the global 438scope. This should be enough to get this code compiling, assuming the 439other usage is correct. 440</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 441 replaced by standardized libraries. 442 In particular, the <code class="classname">unordered_map</code> and 443 <code class="classname">unordered_set</code> containers of TR1 and C++ 2011 444 are suitable replacements for the non-standard 445 <code class="classname">hash_map</code> and <code class="classname">hash_set</code> 446 containers in the SGI STL. 447 </p><p> Header files <code class="filename"><hash_map></code> and <code class="filename"><hash_set></code> moved 448to <code class="filename"><ext/hash_map></code> and <code class="filename"><ext/hash_set></code>, 449respectively. At the same time, all types in these files are enclosed 450in <code class="code">namespace __gnu_cxx</code>. Later versions deprecate 451these files, and suggest using TR1's <code class="filename"><unordered_map></code> 452and <code class="filename"><unordered_set></code> instead. 453</p><p>The extensions are no longer in the global or <code class="code">std</code> 454 namespaces, instead they are declared in the <code class="code">__gnu_cxx</code> 455 namespace. For maximum portability, consider defining a namespace 456 alias to use to talk about extensions, e.g.: 457 </p><pre class="programlisting"> 458 #ifdef __GNUC__ 459 #if __GNUC__ < 3 460 #include <hash_map.h> 461 namespace extension { using ::hash_map; }; // inherit globals 462 #else 463 #include <backward/hash_map> 464 #if __GNUC__ == 3 && __GNUC_MINOR__ == 0 465 namespace extension = std; // GCC 3.0 466 #else 467 namespace extension = ::__gnu_cxx; // GCC 3.1 and later 468 #endif 469 #endif 470 #else // ... there are other compilers, right? 471 namespace extension = std; 472 #endif 473 474 extension::hash_map<int,int> my_map; 475 </pre><p>This is a bit cleaner than defining typedefs for all the 476 instantiations you might need. 477 </p><p>The following autoconf tests check for working HP/SGI hash containers. 478</p><pre class="programlisting"> 479# AC_HEADER_EXT_HASH_MAP 480AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [ 481 AC_CACHE_CHECK(for ext/hash_map, 482 ac_cv_cxx_ext_hash_map, 483 [AC_LANG_SAVE 484 AC_LANG_CPLUSPLUS 485 ac_save_CXXFLAGS="$CXXFLAGS" 486 CXXFLAGS="$CXXFLAGS -Werror" 487 AC_TRY_COMPILE([#include <ext/hash_map>], [using __gnu_cxx::hash_map;], 488 ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no) 489 CXXFLAGS="$ac_save_CXXFLAGS" 490 AC_LANG_RESTORE 491 ]) 492 if test "$ac_cv_cxx_ext_hash_map" = yes; then 493 AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ]) 494 fi 495]) 496</pre><pre class="programlisting"> 497# AC_HEADER_EXT_HASH_SET 498AC_DEFUN([AC_HEADER_EXT_HASH_SET], [ 499 AC_CACHE_CHECK(for ext/hash_set, 500 ac_cv_cxx_ext_hash_set, 501 [AC_LANG_SAVE 502 AC_LANG_CPLUSPLUS 503 ac_save_CXXFLAGS="$CXXFLAGS" 504 CXXFLAGS="$CXXFLAGS -Werror" 505 AC_TRY_COMPILE([#include <ext/hash_set>], [using __gnu_cxx::hash_set;], 506 ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no) 507 CXXFLAGS="$ac_save_CXXFLAGS" 508 AC_LANG_RESTORE 509 ]) 510 if test "$ac_cv_cxx_ext_hash_set" = yes; then 511 AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ]) 512 fi 513]) 514</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>. 515</h4></div></div></div><p>Historically these flags were used with iostreams to control whether 516new files are created or not when opening a file stream, similar to the 517<code class="code">O_CREAT</code> and <code class="code">O_EXCL</code> flags for the 518<code class="function">open(2)</code> system call. Because iostream modes correspond 519to <code class="function">fopen(3)</code> modes these flags are not supported. 520For input streams a new file will not be created anyway, so 521<code class="code">ios::nocreate</code> is not needed. 522For output streams, a new file will be created if it does not exist, which is 523consistent with the behaviour of <code class="function">fopen</code>. 524</p><p>When one of these flags is needed a possible alternative is to attempt 525to open the file using <span class="type">std::ifstream</span> first to determine whether 526the file already exists or not. This may not be reliable however, because 527whether the file exists or not could change between opening the 528<span class="type">std::istream</span> and re-opening with an output stream. If you need 529to check for existence and open a file as a single operation then you will 530need to use OS-specific facilities outside the C++ standard library, such 531as <code class="function">open(2)</code>. 532</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.streamattach"></a> 533No <code class="code">stream::attach(int fd)</code> 534</h4></div></div></div><p> 535 Phil Edwards writes: It was considered and rejected for the ISO 536 standard. Not all environments use file descriptors. Of those 537 that do, not all of them use integers to represent them. 538 </p><p> 539 For a portable solution (among systems which use 540 file descriptors), you need to implement a subclass of 541 <code class="code">std::streambuf</code> (or 542 <code class="code">std::basic_streambuf<..></code>) which opens a file 543 given a descriptor, and then pass an instance of this to the 544 stream-constructor. 545 </p><p> 546 An extension is available that implements this. 547 <code class="filename"><ext/stdio_filebuf.h></code> contains a derived class called 548 <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>. 549 This class can be constructed from a C <code class="code">FILE*</code> or a file 550 descriptor, and provides the <code class="code">fd()</code> function. 551 </p><p> 552 For another example of this, refer to 553 <a class="link" href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a> 554 by Nicolai Josuttis. 555</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx98"></a> 556Support for C++98 dialect. 557</h4></div></div></div><p>Check for complete library coverage of the C++1998/2003 standard. 558</p><pre class="programlisting"> 559# AC_HEADER_STDCXX_98 560AC_DEFUN([AC_HEADER_STDCXX_98], [ 561 AC_CACHE_CHECK(for ISO C++ 98 include files, 562 ac_cv_cxx_stdcxx_98, 563 [AC_LANG_SAVE 564 AC_LANG_CPLUSPLUS 565 AC_TRY_COMPILE([ 566 #include <cassert> 567 #include <cctype> 568 #include <cerrno> 569 #include <cfloat> 570 #include <ciso646> 571 #include <climits> 572 #include <clocale> 573 #include <cmath> 574 #include <csetjmp> 575 #include <csignal> 576 #include <cstdarg> 577 #include <cstddef> 578 #include <cstdio> 579 #include <cstdlib> 580 #include <cstring> 581 #include <ctime> 582 583 #include <algorithm> 584 #include <bitset> 585 #include <complex> 586 #include <deque> 587 #include <exception> 588 #include <fstream> 589 #include <functional> 590 #include <iomanip> 591 #include <ios> 592 #include <iosfwd> 593 #include <iostream> 594 #include <istream> 595 #include <iterator> 596 #include <limits> 597 #include <list> 598 #include <locale> 599 #include <map> 600 #include <memory> 601 #include <new> 602 #include <numeric> 603 #include <ostream> 604 #include <queue> 605 #include <set> 606 #include <sstream> 607 #include <stack> 608 #include <stdexcept> 609 #include <streambuf> 610 #include <string> 611 #include <typeinfo> 612 #include <utility> 613 #include <valarray> 614 #include <vector> 615 ],, 616 ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no) 617 AC_LANG_RESTORE 618 ]) 619 if test "$ac_cv_cxx_stdcxx_98" = yes; then 620 AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ]) 621 fi 622]) 623</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_tr1"></a> 624Support for C++TR1 dialect. 625</h4></div></div></div><p>Check for library coverage of the TR1 standard. 626</p><pre class="programlisting"> 627# AC_HEADER_STDCXX_TR1 628AC_DEFUN([AC_HEADER_STDCXX_TR1], [ 629 AC_CACHE_CHECK(for ISO C++ TR1 include files, 630 ac_cv_cxx_stdcxx_tr1, 631 [AC_LANG_SAVE 632 AC_LANG_CPLUSPLUS 633 AC_TRY_COMPILE([ 634 #include <tr1/array> 635 #include <tr1/ccomplex> 636 #include <tr1/cctype> 637 #include <tr1/cfenv> 638 #include <tr1/cfloat> 639 #include <tr1/cinttypes> 640 #include <tr1/climits> 641 #include <tr1/cmath> 642 #include <tr1/complex> 643 #include <tr1/cstdarg> 644 #include <tr1/cstdbool> 645 #include <tr1/cstdint> 646 #include <tr1/cstdio> 647 #include <tr1/cstdlib> 648 #include <tr1/ctgmath> 649 #include <tr1/ctime> 650 #include <tr1/cwchar> 651 #include <tr1/cwctype> 652 #include <tr1/functional> 653 #include <tr1/memory> 654 #include <tr1/random> 655 #include <tr1/regex> 656 #include <tr1/tuple> 657 #include <tr1/type_traits> 658 #include <tr1/unordered_set> 659 #include <tr1/unordered_map> 660 #include <tr1/utility> 661 ],, 662 ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no) 663 AC_LANG_RESTORE 664 ]) 665 if test "$ac_cv_cxx_stdcxx_tr1" = yes; then 666 AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ]) 667 fi 668]) 669</pre><p>An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>. 670</p><pre class="programlisting"> 671# AC_HEADER_TR1_UNORDERED_MAP 672AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [ 673 AC_CACHE_CHECK(for tr1/unordered_map, 674 ac_cv_cxx_tr1_unordered_map, 675 [AC_LANG_SAVE 676 AC_LANG_CPLUSPLUS 677 AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;], 678 ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no) 679 AC_LANG_RESTORE 680 ]) 681 if test "$ac_cv_cxx_tr1_unordered_map" = yes; then 682 AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ]) 683 fi 684]) 685</pre><pre class="programlisting"> 686# AC_HEADER_TR1_UNORDERED_SET 687AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [ 688 AC_CACHE_CHECK(for tr1/unordered_set, 689 ac_cv_cxx_tr1_unordered_set, 690 [AC_LANG_SAVE 691 AC_LANG_CPLUSPLUS 692 AC_TRY_COMPILE([#include <tr1/unordered_set>], [using std::tr1::unordered_set;], 693 ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no) 694 AC_LANG_RESTORE 695 ]) 696 if test "$ac_cv_cxx_tr1_unordered_set" = yes; then 697 AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ]) 698 fi 699]) 700</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx11"></a> 701Support for C++11 dialect. 702</h4></div></div></div><p>Check for baseline language coverage in the compiler for the C++11 standard. 703</p><pre class="programlisting"> 704# AC_COMPILE_STDCXX_11 705AC_DEFUN([AC_COMPILE_STDCXX_11], [ 706 AC_CACHE_CHECK(if g++ supports C++11 features without additional flags, 707 ac_cv_cxx_compile_cxx11_native, 708 [AC_LANG_SAVE 709 AC_LANG_CPLUSPLUS 710 AC_TRY_COMPILE([ 711 template <typename T> 712 struct check final 713 { 714 static constexpr T value{ __cplusplus }; 715 }; 716 717 typedef check<check<bool>> right_angle_brackets; 718 719 int a; 720 decltype(a) b; 721 722 typedef check<int> check_type; 723 check_type c{}; 724 check_type&& cr = static_cast<check_type&&>(c); 725 726 static_assert(check_type::value == 201103L, "C++11 compiler");],, 727 ac_cv_cxx_compile_cxx11_native=yes, ac_cv_cxx_compile_cxx11_native=no) 728 AC_LANG_RESTORE 729 ]) 730 731 AC_CACHE_CHECK(if g++ supports C++11 features with -std=c++11, 732 ac_cv_cxx_compile_cxx11_cxx, 733 [AC_LANG_SAVE 734 AC_LANG_CPLUSPLUS 735 ac_save_CXXFLAGS="$CXXFLAGS" 736 CXXFLAGS="$CXXFLAGS -std=c++11" 737 AC_TRY_COMPILE([ 738 template <typename T> 739 struct check final 740 { 741 static constexpr T value{ __cplusplus }; 742 }; 743 744 typedef check<check<bool>> right_angle_brackets; 745 746 int a; 747 decltype(a) b; 748 749 typedef check<int> check_type; 750 check_type c{}; 751 check_type&& cr = static_cast<check_type&&>(c); 752 753 static_assert(check_type::value == 201103L, "C++11 compiler");],, 754 ac_cv_cxx_compile_cxx11_cxx=yes, ac_cv_cxx_compile_cxx11_cxx=no) 755 CXXFLAGS="$ac_save_CXXFLAGS" 756 AC_LANG_RESTORE 757 ]) 758 759 AC_CACHE_CHECK(if g++ supports C++11 features with -std=gnu++11, 760 ac_cv_cxx_compile_cxx11_gxx, 761 [AC_LANG_SAVE 762 AC_LANG_CPLUSPLUS 763 ac_save_CXXFLAGS="$CXXFLAGS" 764 CXXFLAGS="$CXXFLAGS -std=gnu++11" 765 AC_TRY_COMPILE([ 766 template <typename T> 767 struct check final 768 { 769 static constexpr T value{ __cplusplus }; 770 }; 771 772 typedef check<check<bool>> right_angle_brackets; 773 774 int a; 775 decltype(a) b; 776 777 typedef check<int> check_type; 778 check_type c{}; 779 check_type&& cr = static_cast<check_type&&>(c); 780 781 static_assert(check_type::value == 201103L, "C++11 compiler");],, 782 ac_cv_cxx_compile_cxx11_gxx=yes, ac_cv_cxx_compile_cxx11_gxx=no) 783 CXXFLAGS="$ac_save_CXXFLAGS" 784 AC_LANG_RESTORE 785 ]) 786 787 if test "$ac_cv_cxx_compile_cxx11_native" = yes || 788 test "$ac_cv_cxx_compile_cxx11_cxx" = yes || 789 test "$ac_cv_cxx_compile_cxx11_gxx" = yes; then 790 AC_DEFINE(HAVE_STDCXX_11,,[Define if g++ supports C++11 features. ]) 791 fi 792]) 793</pre><p>Check for library coverage of the C++2011 standard. 794 (Some library headers are commented out in this check, they are 795 not currently provided by libstdc++). 796</p><pre class="programlisting"> 797# AC_HEADER_STDCXX_11 798AC_DEFUN([AC_HEADER_STDCXX_11], [ 799 AC_CACHE_CHECK(for ISO C++11 include files, 800 ac_cv_cxx_stdcxx_11, 801 [AC_REQUIRE([AC_COMPILE_STDCXX_11]) 802 AC_LANG_SAVE 803 AC_LANG_CPLUSPLUS 804 ac_save_CXXFLAGS="$CXXFLAGS" 805 CXXFLAGS="$CXXFLAGS -std=gnu++11" 806 807 AC_TRY_COMPILE([ 808 #include <cassert> 809 #include <ccomplex> 810 #include <cctype> 811 #include <cerrno> 812 #include <cfenv> 813 #include <cfloat> 814 #include <cinttypes> 815 #include <ciso646> 816 #include <climits> 817 #include <clocale> 818 #include <cmath> 819 #include <csetjmp> 820 #include <csignal> 821 #include <cstdalign> 822 #include <cstdarg> 823 #include <cstdbool> 824 #include <cstddef> 825 #include <cstdint> 826 #include <cstdio> 827 #include <cstdlib> 828 #include <cstring> 829 #include <ctgmath> 830 #include <ctime> 831 // #include <cuchar> 832 #include <cwchar> 833 #include <cwctype> 834 835 #include <algorithm> 836 #include <array> 837 #include <atomic> 838 #include <bitset> 839 #include <chrono> 840 // #include <codecvt> 841 #include <complex> 842 #include <condition_variable> 843 #include <deque> 844 #include <exception> 845 #include <forward_list> 846 #include <fstream> 847 #include <functional> 848 #include <future> 849 #include <initializer_list> 850 #include <iomanip> 851 #include <ios> 852 #include <iosfwd> 853 #include <iostream> 854 #include <istream> 855 #include <iterator> 856 #include <limits> 857 #include <list> 858 #include <locale> 859 #include <map> 860 #include <memory> 861 #include <mutex> 862 #include <new> 863 #include <numeric> 864 #include <ostream> 865 #include <queue> 866 #include <random> 867 #include <ratio> 868 #include <regex> 869 #include <scoped_allocator> 870 #include <set> 871 #include <sstream> 872 #include <stack> 873 #include <stdexcept> 874 #include <streambuf> 875 #include <string> 876 #include <system_error> 877 #include <thread> 878 #include <tuple> 879 #include <typeindex> 880 #include <typeinfo> 881 #include <type_traits> 882 #include <unordered_map> 883 #include <unordered_set> 884 #include <utility> 885 #include <valarray> 886 #include <vector> 887 ],, 888 ac_cv_cxx_stdcxx_11=yes, ac_cv_cxx_stdcxx_11=no) 889 AC_LANG_RESTORE 890 CXXFLAGS="$ac_save_CXXFLAGS" 891 ]) 892 if test "$ac_cv_cxx_stdcxx_11" = yes; then 893 AC_DEFINE(STDCXX_11_HEADERS,,[Define if ISO C++11 header files are present. ]) 894 fi 895]) 896</pre><p>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For 897<code class="filename"><unordered_map></code> 898</p><pre class="programlisting"> 899# AC_HEADER_UNORDERED_MAP 900AC_DEFUN([AC_HEADER_UNORDERED_MAP], [ 901 AC_CACHE_CHECK(for unordered_map, 902 ac_cv_cxx_unordered_map, 903 [AC_REQUIRE([AC_COMPILE_STDCXX_11]) 904 AC_LANG_SAVE 905 AC_LANG_CPLUSPLUS 906 ac_save_CXXFLAGS="$CXXFLAGS" 907 CXXFLAGS="$CXXFLAGS -std=gnu++11" 908 AC_TRY_COMPILE([#include <unordered_map>], [using std::unordered_map;], 909 ac_cv_cxx_unordered_map=yes, ac_cv_cxx_unordered_map=no) 910 CXXFLAGS="$ac_save_CXXFLAGS" 911 AC_LANG_RESTORE 912 ]) 913 if test "$ac_cv_cxx_unordered_map" = yes; then 914 AC_DEFINE(HAVE_UNORDERED_MAP,,[Define if unordered_map is present. ]) 915 fi 916]) 917</pre><pre class="programlisting"> 918# AC_HEADER_UNORDERED_SET 919AC_DEFUN([AC_HEADER_UNORDERED_SET], [ 920 AC_CACHE_CHECK(for unordered_set, 921 ac_cv_cxx_unordered_set, 922 [AC_REQUIRE([AC_COMPILE_STDCXX_11]) 923 AC_LANG_SAVE 924 AC_LANG_CPLUSPLUS 925 ac_save_CXXFLAGS="$CXXFLAGS" 926 CXXFLAGS="$CXXFLAGS -std=gnu++11" 927 AC_TRY_COMPILE([#include <unordered_set>], [using std::unordered_set;], 928 ac_cv_cxx_unordered_set=yes, ac_cv_cxx_unordered_set=no) 929 CXXFLAGS="$ac_save_CXXFLAGS" 930 AC_LANG_RESTORE 931 ]) 932 if test "$ac_cv_cxx_unordered_set" = yes; then 933 AC_DEFINE(HAVE_UNORDERED_SET,,[Define if unordered_set is present. ]) 934 fi 935]) 936</pre><p> 937 Some C++11 features first appeared in GCC 4.3 and could be enabled by 938 <code class="option">-std=c++0x</code> and <code class="option">-std=gnu++0x</code> for GCC 939 releases which pre-date the 2011 standard. Those C++11 features and GCC's 940 support for them were still changing until the 2011 standard was finished, 941 but the autoconf checks above could be extended to test for incomplete 942 C++11 support with <code class="option">-std=c++0x</code> and 943 <code class="option">-std=gnu++0x</code>. 944</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.iterator_type"></a> 945 <code class="code">Container::iterator_type</code> is not necessarily <code class="code">Container::value_type*</code> 946</h4></div></div></div><p> 947 This is a change in behavior from older versions. Now, most 948 <span class="type">iterator_type</span> typedefs in container classes are POD 949 objects, not <span class="type">value_type</span> pointers. 950</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="id-1.3.6.3.8.5.2"></a><p><span class="title"><em> 951 <a class="link" href="http://www.kegel.com/gcc/gcc4.html" target="_top"> 952 Migrating to GCC 4.1 953 </a> 954 </em>. </span><span class="author"><span class="firstname">Dan</span> <span class="surname">Kegel</span>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.8.5.3"></a><p><span class="title"><em> 955 <a class="link" href="http://lists.debian.org/debian-gcc/2006/03/msg00405.html" target="_top"> 956 Building the Whole Debian Archive with GCC 4.1: A Summary 957 </a> 958 </em>. </span><span class="author"><span class="firstname">Martin</span> <span class="surname">Michlmayr</span>. </span></p></div><div class="biblioentry"><a id="id-1.3.6.3.8.5.4"></a><p><span class="title"><em> 959 <a class="link" href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html" target="_top"> 960 Migration guide for GCC-3.2 961 </a> 962 </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.�� 963 Free Software Needs Free Documentation 964 965</td></tr></table></div></body></html>