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 Stylesheets Vsnapshot" /><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 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 not supported. 371</p><p>For those of you new to ISO C++ (welcome, time travelers!), the 372 ancient pre-ISO headers have new names. 373 The C++ FAQ has a good explanation in <a class="link" href="https://isocpp.org/wiki/faq/coding-standards#std-headers" target="_top">What's 374 the difference between <xxx> and <xxx.h> headers?</a>. 375 </p><p>Porting between pre-ISO headers and ISO headers is simple: headers 376like <code class="filename"><vector.h></code> can be replaced with <code class="filename"><vector></code> and a using 377directive <code class="code">using namespace std;</code> can be put at the global 378scope. This should be enough to get this code compiling, assuming the 379other usage is correct. 380</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 381 replaced by standardized libraries. 382 In particular, the <code class="classname">unordered_map</code> and 383 <code class="classname">unordered_set</code> containers of TR1 and C++ 2011 384 are suitable replacements for the non-standard 385 <code class="classname">hash_map</code> and <code class="classname">hash_set</code> 386 containers in the SGI STL. 387 </p><p> Header files <code class="filename"><hash_map></code> and <code class="filename"><hash_set></code> moved 388to <code class="filename"><ext/hash_map></code> and <code class="filename"><ext/hash_set></code>, 389respectively. At the same time, all types in these files are enclosed 390in <code class="code">namespace __gnu_cxx</code>. Later versions deprecate 391these files, and suggest using TR1's <code class="filename"><unordered_map></code> 392and <code class="filename"><unordered_set></code> instead. 393</p><p>The extensions are no longer in the global or <code class="code">std</code> 394 namespaces, instead they are declared in the <code class="code">__gnu_cxx</code> 395 namespace. For maximum portability, consider defining a namespace 396 alias to use to talk about extensions, e.g.: 397 </p><pre class="programlisting"> 398 #ifdef __GNUC__ 399 #if __GNUC__ < 3 400 #include <hash_map.h> 401 namespace extension { using ::hash_map; }; // inherit globals 402 #else 403 #include <backward/hash_map> 404 #if __GNUC__ == 3 && __GNUC_MINOR__ == 0 405 namespace extension = std; // GCC 3.0 406 #else 407 namespace extension = ::__gnu_cxx; // GCC 3.1 and later 408 #endif 409 #endif 410 #else // ... there are other compilers, right? 411 namespace extension = std; 412 #endif 413 414 extension::hash_map<int,int> my_map; 415 </pre><p>This is a bit cleaner than defining typedefs for all the 416 instantiations you might need. 417 </p><p>The following autoconf tests check for working HP/SGI hash containers. 418</p><pre class="programlisting"> 419# AC_HEADER_EXT_HASH_MAP 420AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [ 421 AC_CACHE_CHECK(for ext/hash_map, 422 ac_cv_cxx_ext_hash_map, 423 [AC_LANG_SAVE 424 AC_LANG_CPLUSPLUS 425 ac_save_CXXFLAGS="$CXXFLAGS" 426 CXXFLAGS="$CXXFLAGS -Werror" 427 AC_TRY_COMPILE([#include <ext/hash_map>], [using __gnu_cxx::hash_map;], 428 ac_cv_cxx_ext_hash_map=yes, ac_cv_cxx_ext_hash_map=no) 429 CXXFLAGS="$ac_save_CXXFLAGS" 430 AC_LANG_RESTORE 431 ]) 432 if test "$ac_cv_cxx_ext_hash_map" = yes; then 433 AC_DEFINE(HAVE_EXT_HASH_MAP,,[Define if ext/hash_map is present. ]) 434 fi 435]) 436</pre><pre class="programlisting"> 437# AC_HEADER_EXT_HASH_SET 438AC_DEFUN([AC_HEADER_EXT_HASH_SET], [ 439 AC_CACHE_CHECK(for ext/hash_set, 440 ac_cv_cxx_ext_hash_set, 441 [AC_LANG_SAVE 442 AC_LANG_CPLUSPLUS 443 ac_save_CXXFLAGS="$CXXFLAGS" 444 CXXFLAGS="$CXXFLAGS -Werror" 445 AC_TRY_COMPILE([#include <ext/hash_set>], [using __gnu_cxx::hash_set;], 446 ac_cv_cxx_ext_hash_set=yes, ac_cv_cxx_ext_hash_set=no) 447 CXXFLAGS="$ac_save_CXXFLAGS" 448 AC_LANG_RESTORE 449 ]) 450 if test "$ac_cv_cxx_ext_hash_set" = yes; then 451 AC_DEFINE(HAVE_EXT_HASH_SET,,[Define if ext/hash_set is present. ]) 452 fi 453]) 454</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>. 455</h4></div></div></div><p>Historically these flags were used with iostreams to control whether 456new files are created or not when opening a file stream, similar to the 457<code class="code">O_CREAT</code> and <code class="code">O_EXCL</code> flags for the 458<code class="function">open(2)</code> system call. Because iostream modes correspond 459to <code class="function">fopen(3)</code> modes these flags are not supported. 460For input streams a new file will not be created anyway, so 461<code class="code">ios::nocreate</code> is not needed. 462For output streams, a new file will be created if it does not exist, which is 463consistent with the behaviour of <code class="function">fopen</code>. 464</p><p>When one of these flags is needed a possible alternative is to attempt 465to open the file using <span class="type">std::ifstream</span> first to determine whether 466the file already exists or not. This may not be reliable however, because 467whether the file exists or not could change between opening the 468<span class="type">std::istream</span> and re-opening with an output stream. If you need 469to check for existence and open a file as a single operation then you will 470need to use OS-specific facilities outside the C++ standard library, such 471as <code class="function">open(2)</code>. 472</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.streamattach"></a> 473No <code class="code">stream::attach(int fd)</code> 474</h4></div></div></div><p> 475 Phil Edwards writes: It was considered and rejected for the ISO 476 standard. Not all environments use file descriptors. Of those 477 that do, not all of them use integers to represent them. 478 </p><p> 479 For a portable solution (among systems which use 480 file descriptors), you need to implement a subclass of 481 <code class="code">std::streambuf</code> (or 482 <code class="code">std::basic_streambuf<..></code>) which opens a file 483 given a descriptor, and then pass an instance of this to the 484 stream-constructor. 485 </p><p> 486 An extension is available that implements this. 487 <code class="filename"><ext/stdio_filebuf.h></code> contains a derived class called 488 <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>. 489 This class can be constructed from a C <code class="code">FILE*</code> or a file 490 descriptor, and provides the <code class="code">fd()</code> function. 491 </p><p> 492 For another example of this, refer to 493 <a class="link" href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a> 494 by Nicolai Josuttis. 495</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx98"></a> 496Support for C++98 dialect. 497</h4></div></div></div><p>Check for complete library coverage of the C++1998/2003 standard. 498</p><pre class="programlisting"> 499# AC_HEADER_STDCXX_98 500AC_DEFUN([AC_HEADER_STDCXX_98], [ 501 AC_CACHE_CHECK(for ISO C++ 98 include files, 502 ac_cv_cxx_stdcxx_98, 503 [AC_LANG_SAVE 504 AC_LANG_CPLUSPLUS 505 AC_TRY_COMPILE([ 506 #include <cassert> 507 #include <cctype> 508 #include <cerrno> 509 #include <cfloat> 510 #include <ciso646> 511 #include <climits> 512 #include <clocale> 513 #include <cmath> 514 #include <csetjmp> 515 #include <csignal> 516 #include <cstdarg> 517 #include <cstddef> 518 #include <cstdio> 519 #include <cstdlib> 520 #include <cstring> 521 #include <ctime> 522 523 #include <algorithm> 524 #include <bitset> 525 #include <complex> 526 #include <deque> 527 #include <exception> 528 #include <fstream> 529 #include <functional> 530 #include <iomanip> 531 #include <ios> 532 #include <iosfwd> 533 #include <iostream> 534 #include <istream> 535 #include <iterator> 536 #include <limits> 537 #include <list> 538 #include <locale> 539 #include <map> 540 #include <memory> 541 #include <new> 542 #include <numeric> 543 #include <ostream> 544 #include <queue> 545 #include <set> 546 #include <sstream> 547 #include <stack> 548 #include <stdexcept> 549 #include <streambuf> 550 #include <string> 551 #include <typeinfo> 552 #include <utility> 553 #include <valarray> 554 #include <vector> 555 ],, 556 ac_cv_cxx_stdcxx_98=yes, ac_cv_cxx_stdcxx_98=no) 557 AC_LANG_RESTORE 558 ]) 559 if test "$ac_cv_cxx_stdcxx_98" = yes; then 560 AC_DEFINE(STDCXX_98_HEADERS,,[Define if ISO C++ 1998 header files are present. ]) 561 fi 562]) 563</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_tr1"></a> 564Support for C++TR1 dialect. 565</h4></div></div></div><p>Check for library coverage of the TR1 standard. 566</p><pre class="programlisting"> 567# AC_HEADER_STDCXX_TR1 568AC_DEFUN([AC_HEADER_STDCXX_TR1], [ 569 AC_CACHE_CHECK(for ISO C++ TR1 include files, 570 ac_cv_cxx_stdcxx_tr1, 571 [AC_LANG_SAVE 572 AC_LANG_CPLUSPLUS 573 AC_TRY_COMPILE([ 574 #include <tr1/array> 575 #include <tr1/ccomplex> 576 #include <tr1/cctype> 577 #include <tr1/cfenv> 578 #include <tr1/cfloat> 579 #include <tr1/cinttypes> 580 #include <tr1/climits> 581 #include <tr1/cmath> 582 #include <tr1/complex> 583 #include <tr1/cstdarg> 584 #include <tr1/cstdbool> 585 #include <tr1/cstdint> 586 #include <tr1/cstdio> 587 #include <tr1/cstdlib> 588 #include <tr1/ctgmath> 589 #include <tr1/ctime> 590 #include <tr1/cwchar> 591 #include <tr1/cwctype> 592 #include <tr1/functional> 593 #include <tr1/memory> 594 #include <tr1/random> 595 #include <tr1/regex> 596 #include <tr1/tuple> 597 #include <tr1/type_traits> 598 #include <tr1/unordered_set> 599 #include <tr1/unordered_map> 600 #include <tr1/utility> 601 ],, 602 ac_cv_cxx_stdcxx_tr1=yes, ac_cv_cxx_stdcxx_tr1=no) 603 AC_LANG_RESTORE 604 ]) 605 if test "$ac_cv_cxx_stdcxx_tr1" = yes; then 606 AC_DEFINE(STDCXX_TR1_HEADERS,,[Define if ISO C++ TR1 header files are present. ]) 607 fi 608]) 609</pre><p>An alternative is to check just for specific TR1 includes, such as <unordered_map> and <unordered_set>. 610</p><pre class="programlisting"> 611# AC_HEADER_TR1_UNORDERED_MAP 612AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [ 613 AC_CACHE_CHECK(for tr1/unordered_map, 614 ac_cv_cxx_tr1_unordered_map, 615 [AC_LANG_SAVE 616 AC_LANG_CPLUSPLUS 617 AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;], 618 ac_cv_cxx_tr1_unordered_map=yes, ac_cv_cxx_tr1_unordered_map=no) 619 AC_LANG_RESTORE 620 ]) 621 if test "$ac_cv_cxx_tr1_unordered_map" = yes; then 622 AC_DEFINE(HAVE_TR1_UNORDERED_MAP,,[Define if tr1/unordered_map is present. ]) 623 fi 624]) 625</pre><pre class="programlisting"> 626# AC_HEADER_TR1_UNORDERED_SET 627AC_DEFUN([AC_HEADER_TR1_UNORDERED_SET], [ 628 AC_CACHE_CHECK(for tr1/unordered_set, 629 ac_cv_cxx_tr1_unordered_set, 630 [AC_LANG_SAVE 631 AC_LANG_CPLUSPLUS 632 AC_TRY_COMPILE([#include <tr1/unordered_set>], [using std::tr1::unordered_set;], 633 ac_cv_cxx_tr1_unordered_set=yes, ac_cv_cxx_tr1_unordered_set=no) 634 AC_LANG_RESTORE 635 ]) 636 if test "$ac_cv_cxx_tr1_unordered_set" = yes; then 637 AC_DEFINE(HAVE_TR1_UNORDERED_SET,,[Define if tr1/unordered_set is present. ]) 638 fi 639]) 640</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.support_cxx11"></a> 641Support for C++11 dialect. 642</h4></div></div></div><p>Check for baseline language coverage in the compiler for the C++11 standard. 643</p><pre class="programlisting"> 644# AC_COMPILE_STDCXX_11 645AC_DEFUN([AC_COMPILE_STDCXX_11], [ 646 AC_CACHE_CHECK(if g++ supports C++11 features without additional flags, 647 ac_cv_cxx_compile_cxx11_native, 648 [AC_LANG_SAVE 649 AC_LANG_CPLUSPLUS 650 AC_TRY_COMPILE([ 651 template <typename T> 652 struct check final 653 { 654 static constexpr T value{ __cplusplus }; 655 }; 656 657 typedef check<check<bool>> right_angle_brackets; 658 659 int a; 660 decltype(a) b; 661 662 typedef check<int> check_type; 663 check_type c{}; 664 check_type&& cr = static_cast<check_type&&>(c); 665 666 static_assert(check_type::value == 201103L, "C++11 compiler");],, 667 ac_cv_cxx_compile_cxx11_native=yes, ac_cv_cxx_compile_cxx11_native=no) 668 AC_LANG_RESTORE 669 ]) 670 671 AC_CACHE_CHECK(if g++ supports C++11 features with -std=c++11, 672 ac_cv_cxx_compile_cxx11_cxx, 673 [AC_LANG_SAVE 674 AC_LANG_CPLUSPLUS 675 ac_save_CXXFLAGS="$CXXFLAGS" 676 CXXFLAGS="$CXXFLAGS -std=c++11" 677 AC_TRY_COMPILE([ 678 template <typename T> 679 struct check final 680 { 681 static constexpr T value{ __cplusplus }; 682 }; 683 684 typedef check<check<bool>> right_angle_brackets; 685 686 int a; 687 decltype(a) b; 688 689 typedef check<int> check_type; 690 check_type c{}; 691 check_type&& cr = static_cast<check_type&&>(c); 692 693 static_assert(check_type::value == 201103L, "C++11 compiler");],, 694 ac_cv_cxx_compile_cxx11_cxx=yes, ac_cv_cxx_compile_cxx11_cxx=no) 695 CXXFLAGS="$ac_save_CXXFLAGS" 696 AC_LANG_RESTORE 697 ]) 698 699 AC_CACHE_CHECK(if g++ supports C++11 features with -std=gnu++11, 700 ac_cv_cxx_compile_cxx11_gxx, 701 [AC_LANG_SAVE 702 AC_LANG_CPLUSPLUS 703 ac_save_CXXFLAGS="$CXXFLAGS" 704 CXXFLAGS="$CXXFLAGS -std=gnu++11" 705 AC_TRY_COMPILE([ 706 template <typename T> 707 struct check final 708 { 709 static constexpr T value{ __cplusplus }; 710 }; 711 712 typedef check<check<bool>> right_angle_brackets; 713 714 int a; 715 decltype(a) b; 716 717 typedef check<int> check_type; 718 check_type c{}; 719 check_type&& cr = static_cast<check_type&&>(c); 720 721 static_assert(check_type::value == 201103L, "C++11 compiler");],, 722 ac_cv_cxx_compile_cxx11_gxx=yes, ac_cv_cxx_compile_cxx11_gxx=no) 723 CXXFLAGS="$ac_save_CXXFLAGS" 724 AC_LANG_RESTORE 725 ]) 726 727 if test "$ac_cv_cxx_compile_cxx11_native" = yes || 728 test "$ac_cv_cxx_compile_cxx11_cxx" = yes || 729 test "$ac_cv_cxx_compile_cxx11_gxx" = yes; then 730 AC_DEFINE(HAVE_STDCXX_11,,[Define if g++ supports C++11 features. ]) 731 fi 732]) 733</pre><p>Check for library coverage of the C++2011 standard. 734 (Some library headers are commented out in this check, they are 735 not currently provided by libstdc++). 736</p><pre class="programlisting"> 737# AC_HEADER_STDCXX_11 738AC_DEFUN([AC_HEADER_STDCXX_11], [ 739 AC_CACHE_CHECK(for ISO C++11 include files, 740 ac_cv_cxx_stdcxx_11, 741 [AC_REQUIRE([AC_COMPILE_STDCXX_11]) 742 AC_LANG_SAVE 743 AC_LANG_CPLUSPLUS 744 ac_save_CXXFLAGS="$CXXFLAGS" 745 CXXFLAGS="$CXXFLAGS -std=gnu++11" 746 747 AC_TRY_COMPILE([ 748 #include <cassert> 749 #include <ccomplex> 750 #include <cctype> 751 #include <cerrno> 752 #include <cfenv> 753 #include <cfloat> 754 #include <cinttypes> 755 #include <ciso646> 756 #include <climits> 757 #include <clocale> 758 #include <cmath> 759 #include <csetjmp> 760 #include <csignal> 761 #include <cstdalign> 762 #include <cstdarg> 763 #include <cstdbool> 764 #include <cstddef> 765 #include <cstdint> 766 #include <cstdio> 767 #include <cstdlib> 768 #include <cstring> 769 #include <ctgmath> 770 #include <ctime> 771 // #include <cuchar> 772 #include <cwchar> 773 #include <cwctype> 774 775 #include <algorithm> 776 #include <array> 777 #include <atomic> 778 #include <bitset> 779 #include <chrono> 780 // #include <codecvt> 781 #include <complex> 782 #include <condition_variable> 783 #include <deque> 784 #include <exception> 785 #include <forward_list> 786 #include <fstream> 787 #include <functional> 788 #include <future> 789 #include <initializer_list> 790 #include <iomanip> 791 #include <ios> 792 #include <iosfwd> 793 #include <iostream> 794 #include <istream> 795 #include <iterator> 796 #include <limits> 797 #include <list> 798 #include <locale> 799 #include <map> 800 #include <memory> 801 #include <mutex> 802 #include <new> 803 #include <numeric> 804 #include <ostream> 805 #include <queue> 806 #include <random> 807 #include <ratio> 808 #include <regex> 809 #include <scoped_allocator> 810 #include <set> 811 #include <sstream> 812 #include <stack> 813 #include <stdexcept> 814 #include <streambuf> 815 #include <string> 816 #include <system_error> 817 #include <thread> 818 #include <tuple> 819 #include <typeindex> 820 #include <typeinfo> 821 #include <type_traits> 822 #include <unordered_map> 823 #include <unordered_set> 824 #include <utility> 825 #include <valarray> 826 #include <vector> 827 ],, 828 ac_cv_cxx_stdcxx_11=yes, ac_cv_cxx_stdcxx_11=no) 829 AC_LANG_RESTORE 830 CXXFLAGS="$ac_save_CXXFLAGS" 831 ]) 832 if test "$ac_cv_cxx_stdcxx_11" = yes; then 833 AC_DEFINE(STDCXX_11_HEADERS,,[Define if ISO C++11 header files are present. ]) 834 fi 835]) 836</pre><p>As is the case for TR1 support, these autoconf macros can be made for a finer-grained, per-header-file check. For 837<code class="filename"><unordered_map></code> 838</p><pre class="programlisting"> 839# AC_HEADER_UNORDERED_MAP 840AC_DEFUN([AC_HEADER_UNORDERED_MAP], [ 841 AC_CACHE_CHECK(for unordered_map, 842 ac_cv_cxx_unordered_map, 843 [AC_REQUIRE([AC_COMPILE_STDCXX_11]) 844 AC_LANG_SAVE 845 AC_LANG_CPLUSPLUS 846 ac_save_CXXFLAGS="$CXXFLAGS" 847 CXXFLAGS="$CXXFLAGS -std=gnu++11" 848 AC_TRY_COMPILE([#include <unordered_map>], [using std::unordered_map;], 849 ac_cv_cxx_unordered_map=yes, ac_cv_cxx_unordered_map=no) 850 CXXFLAGS="$ac_save_CXXFLAGS" 851 AC_LANG_RESTORE 852 ]) 853 if test "$ac_cv_cxx_unordered_map" = yes; then 854 AC_DEFINE(HAVE_UNORDERED_MAP,,[Define if unordered_map is present. ]) 855 fi 856]) 857</pre><pre class="programlisting"> 858# AC_HEADER_UNORDERED_SET 859AC_DEFUN([AC_HEADER_UNORDERED_SET], [ 860 AC_CACHE_CHECK(for unordered_set, 861 ac_cv_cxx_unordered_set, 862 [AC_REQUIRE([AC_COMPILE_STDCXX_11]) 863 AC_LANG_SAVE 864 AC_LANG_CPLUSPLUS 865 ac_save_CXXFLAGS="$CXXFLAGS" 866 CXXFLAGS="$CXXFLAGS -std=gnu++11" 867 AC_TRY_COMPILE([#include <unordered_set>], [using std::unordered_set;], 868 ac_cv_cxx_unordered_set=yes, ac_cv_cxx_unordered_set=no) 869 CXXFLAGS="$ac_save_CXXFLAGS" 870 AC_LANG_RESTORE 871 ]) 872 if test "$ac_cv_cxx_unordered_set" = yes; then 873 AC_DEFINE(HAVE_UNORDERED_SET,,[Define if unordered_set is present. ]) 874 fi 875]) 876</pre><p> 877 Some C++11 features first appeared in GCC 4.3 and could be enabled by 878 <code class="option">-std=c++0x</code> and <code class="option">-std=gnu++0x</code> for GCC 879 releases which pre-date the 2011 standard. Those C++11 features and GCC's 880 support for them were still changing until the 2011 standard was finished, 881 but the autoconf checks above could be extended to test for incomplete 882 C++11 support with <code class="option">-std=c++0x</code> and 883 <code class="option">-std=gnu++0x</code>. 884</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="backwards.third.iterator_type"></a> 885 <code class="code">Container::iterator_type</code> is not necessarily <code class="code">Container::value_type*</code> 886</h4></div></div></div><p> 887 This is a change in behavior from older versions. Now, most 888 <span class="type">iterator_type</span> typedefs in container classes are POD 889 objects, not <span class="type">value_type</span> pointers. 890</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> 891 <a class="link" href="http://www.kegel.com/gcc/gcc4.html" target="_top"> 892 Migrating to GCC 4.1 893 </a> 894 </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> 895 <a class="link" href="https://lists.debian.org/debian-gcc/2006/03/msg00405.html" target="_top"> 896 Building the Whole Debian Archive with GCC 4.1: A Summary 897 </a> 898 </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> 899 <a class="link" href="http://annwm.lbl.gov/~leggett/Atlas/gcc-3.2.html" target="_top"> 900 Migration guide for GCC-3.2 901 </a> 902 </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. 903 Free Software Needs Free Documentation 904 905</td></tr></table></div></body></html>