1 <chapter xmlns="http://docbook.org/ns/docbook" version="5.0"
2 xml:id="manual.intro.using" xreflabel="Using">
3 <info><title>Using</title></info>
4 <?dbhtml filename="using.html"?>
6 <section xml:id="manual.intro.using.flags" xreflabel="Flags"><info><title>Command Options</title></info>
9 The set of features available in the GNU C++ library is shaped
11 several <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Invoking-GCC.html">GCC
12 Command Options</link>. Options that impact libstdc++ are
13 enumerated and detailed in the table below.
17 By default, <command>g++</command> is equivalent to <command>g++ -std=gnu++98</command>. The standard library also defaults to this dialect.
21 <title>C++ Command Options</title>
23 <tgroup cols="2" align="left" colsep="1" rowsep="1">
24 <colspec colname="c1"/>
25 <colspec colname="c2"/>
29 <entry>Option Flags</entry>
30 <entry>Description</entry>
36 <entry><literal>-std=c++98</literal></entry>
37 <entry>Use the 1998 ISO C++ standard plus amendments.</entry>
41 <entry><literal>-std=gnu++98</literal></entry>
42 <entry>As directly above, with GNU extensions.</entry>
46 <entry><literal>-std=c++11</literal></entry>
47 <entry>Use the 2011 ISO C++ standard.</entry>
51 <entry><literal>-std=gnu++11</literal></entry>
52 <entry>As directly above, with GNU extensions.</entry>
56 <entry><literal>-fexceptions</literal></entry>
57 <entry>See <link linkend="intro.using.exception.no">exception-free dialect</link></entry>
61 <entry><literal>-frtti</literal></entry>
62 <entry>As above, but RTTI-free dialect.</entry>
66 <entry><literal>-pthread</literal> or <literal>-pthreads</literal></entry>
67 <entry>For ISO C++11 <thread>, <future>,
68 <mutex>, or <condition_variable>.</entry>
72 <entry><literal>-fopenmp</literal></entry>
73 <entry>For <link linkend="manual.ext.parallel_mode">parallel</link> mode.</entry>
82 <section xml:id="manual.intro.using.headers" xreflabel="Headers"><info><title>Headers</title></info>
83 <?dbhtml filename="using_headers.html"?>
86 <section xml:id="manual.intro.using.headers.all" xreflabel="Header Files"><info><title>Header Files</title></info>
90 The C++ standard specifies the entire set of header files that
91 must be available to all hosted implementations. Actually, the
92 word "files" is a misnomer, since the contents of the
93 headers don't necessarily have to be in any kind of external
94 file. The only rule is that when one <code>#include</code>'s a
95 header, the contents of that header become available, no matter
100 That said, in practice files are used.
104 There are two main types of include files: header files related
105 to a specific version of the ISO C++ standard (called Standard
106 Headers), and all others (TR1, C++ ABI, and Extensions).
110 Two dialects of standard headers are supported, corresponding to
111 the 1998 standard as updated for 2003, and the current 2011 standard.
115 C++98/03 include files. These are available in the default compilation mode, i.e. <code>-std=c++98</code> or <code>-std=gnu++98</code>.
119 <title>C++ 1998 Library Headers</title>
121 <tgroup cols="5" align="left" colsep="1" rowsep="1">
122 <colspec colname="c1"/>
123 <colspec colname="c2"/>
124 <colspec colname="c3"/>
125 <colspec colname="c4"/>
126 <colspec colname="c5"/>
129 <entry><filename class="headerfile">algorithm</filename></entry>
130 <entry><filename class="headerfile">bitset</filename></entry>
131 <entry><filename class="headerfile">complex</filename></entry>
132 <entry><filename class="headerfile">deque</filename></entry>
133 <entry><filename class="headerfile">exception</filename></entry>
136 <entry><filename class="headerfile">fstream</filename></entry>
137 <entry><filename class="headerfile">functional</filename></entry>
138 <entry><filename class="headerfile">iomanip</filename></entry>
139 <entry><filename class="headerfile">ios</filename></entry>
140 <entry><filename class="headerfile">iosfwd</filename></entry>
143 <entry><filename class="headerfile">iostream</filename></entry>
144 <entry><filename class="headerfile">istream</filename></entry>
145 <entry><filename class="headerfile">iterator</filename></entry>
146 <entry><filename class="headerfile">limits</filename></entry>
147 <entry><filename class="headerfile">list</filename></entry>
150 <entry><filename class="headerfile">locale</filename></entry>
151 <entry><filename class="headerfile">map</filename></entry>
152 <entry><filename class="headerfile">memory</filename></entry>
153 <entry><filename class="headerfile">new</filename></entry>
154 <entry><filename class="headerfile">numeric</filename></entry>
157 <entry><filename class="headerfile">ostream</filename></entry>
158 <entry><filename class="headerfile">queue</filename></entry>
159 <entry><filename class="headerfile">set</filename></entry>
160 <entry><filename class="headerfile">sstream</filename></entry>
161 <entry><filename class="headerfile">stack</filename></entry>
164 <entry><filename class="headerfile">stdexcept</filename></entry>
165 <entry><filename class="headerfile">streambuf</filename></entry>
166 <entry><filename class="headerfile">string</filename></entry>
167 <entry><filename class="headerfile">utility</filename></entry>
168 <entry><filename class="headerfile">typeinfo</filename></entry>
171 <entry><filename class="headerfile">valarray</filename></entry>
172 <entry><filename class="headerfile">vector</filename></entry>
180 <title>C++ 1998 Library Headers for C Library Facilities</title>
182 <tgroup cols="5" align="left" colsep="1" rowsep="1">
183 <colspec colname="c1"/>
184 <colspec colname="c2"/>
185 <colspec colname="c3"/>
186 <colspec colname="c4"/>
187 <colspec colname="c5"/>
190 <entry><filename class="headerfile">cassert</filename></entry>
191 <entry><filename class="headerfile">cerrno</filename></entry>
192 <entry><filename class="headerfile">cctype</filename></entry>
193 <entry><filename class="headerfile">cfloat</filename></entry>
194 <entry><filename class="headerfile">ciso646</filename></entry>
197 <entry><filename class="headerfile">climits</filename></entry>
198 <entry><filename class="headerfile">clocale</filename></entry>
199 <entry><filename class="headerfile">cmath</filename></entry>
200 <entry><filename class="headerfile">csetjmp</filename></entry>
201 <entry><filename class="headerfile">csignal</filename></entry>
204 <entry><filename class="headerfile">cstdarg</filename></entry>
205 <entry><filename class="headerfile">cstddef</filename></entry>
206 <entry><filename class="headerfile">cstdio</filename></entry>
207 <entry><filename class="headerfile">cstdlib</filename></entry>
208 <entry><filename class="headerfile">cstring</filename></entry>
211 <entry><filename class="headerfile">ctime</filename></entry>
212 <entry><filename class="headerfile">cwchar</filename></entry>
213 <entry><filename class="headerfile">cwctype</filename></entry>
220 C++11 include files. These are only available in C++11 compilation
221 mode, i.e. <literal>-std=c++11</literal> or <literal>-std=gnu++11</literal>.
226 <title>C++ 2011 Library Headers</title>
228 <tgroup cols="5" align="left" colsep="1" rowsep="1">
229 <colspec colname="c1"/>
230 <colspec colname="c2"/>
231 <colspec colname="c3"/>
232 <colspec colname="c4"/>
233 <colspec colname="c5"/>
237 <entry><filename class="headerfile">algorithm</filename></entry>
238 <entry><filename class="headerfile">array</filename></entry>
239 <entry><filename class="headerfile">bitset</filename></entry>
240 <entry><filename class="headerfile">chrono</filename></entry>
241 <entry><filename class="headerfile">complex</filename></entry>
244 <entry><filename class="headerfile">condition_variable</filename></entry>
245 <entry><filename class="headerfile">deque</filename></entry>
246 <entry><filename class="headerfile">exception</filename></entry>
247 <entry><filename class="headerfile">forward_list</filename></entry>
248 <entry><filename class="headerfile">fstream</filename></entry>
251 <entry><filename class="headerfile">functional</filename></entry>
252 <entry><filename class="headerfile">future</filename></entry>
253 <entry><filename class="headerfile">initalizer_list</filename></entry>
254 <entry><filename class="headerfile">iomanip</filename></entry>
255 <entry><filename class="headerfile">ios</filename></entry>
258 <entry><filename class="headerfile">iosfwd</filename></entry>
259 <entry><filename class="headerfile">iostream</filename></entry>
260 <entry><filename class="headerfile">istream</filename></entry>
261 <entry><filename class="headerfile">iterator</filename></entry>
262 <entry><filename class="headerfile">limits</filename></entry>
265 <entry><filename class="headerfile">list</filename></entry>
266 <entry><filename class="headerfile">locale</filename></entry>
267 <entry><filename class="headerfile">map</filename></entry>
268 <entry><filename class="headerfile">memory</filename></entry>
269 <entry><filename class="headerfile">mutex</filename></entry>
272 <entry><filename class="headerfile">new</filename></entry>
273 <entry><filename class="headerfile">numeric</filename></entry>
274 <entry><filename class="headerfile">ostream</filename></entry>
275 <entry><filename class="headerfile">queue</filename></entry>
276 <entry><filename class="headerfile">random</filename></entry>
279 <entry><filename class="headerfile">ratio</filename></entry>
280 <entry><filename class="headerfile">regex</filename></entry>
281 <entry><filename class="headerfile">set</filename></entry>
282 <entry><filename class="headerfile">sstream</filename></entry>
283 <entry><filename class="headerfile">stack</filename></entry>
286 <entry><filename class="headerfile">stdexcept</filename></entry>
287 <entry><filename class="headerfile">streambuf</filename></entry>
288 <entry><filename class="headerfile">string</filename></entry>
289 <entry><filename class="headerfile">system_error</filename></entry>
290 <entry><filename class="headerfile">thread</filename></entry>
293 <entry><filename class="headerfile">tuple</filename></entry>
294 <entry><filename class="headerfile">type_traits</filename></entry>
295 <entry><filename class="headerfile">typeinfo</filename></entry>
296 <entry><filename class="headerfile">unordered_map</filename></entry>
297 <entry><filename class="headerfile">unordered_set</filename></entry>
300 <entry><filename class="headerfile">utility</filename></entry>
301 <entry><filename class="headerfile">valarray</filename></entry>
302 <entry><filename class="headerfile">vector</filename></entry>
312 <title>C++ 2011 Library Headers for C Library Facilities</title>
314 <tgroup cols="5" align="left" colsep="1" rowsep="1">
315 <colspec colname="c1"/>
316 <colspec colname="c2"/>
317 <colspec colname="c3"/>
318 <colspec colname="c4"/>
319 <colspec colname="c5"/>
322 <entry><filename class="headerfile">cassert</filename></entry>
323 <entry><filename class="headerfile">ccomplex</filename></entry>
324 <entry><filename class="headerfile">cctype</filename></entry>
325 <entry><filename class="headerfile">cerrno</filename></entry>
326 <entry><filename class="headerfile">cfenv</filename></entry>
329 <entry><filename class="headerfile">cfloat</filename></entry>
330 <entry><filename class="headerfile">cinttypes</filename></entry>
331 <entry><filename class="headerfile">ciso646</filename></entry>
332 <entry><filename class="headerfile">climits</filename></entry>
333 <entry><filename class="headerfile">clocale</filename></entry>
336 <entry><filename class="headerfile">cmath</filename></entry>
337 <entry><filename class="headerfile">csetjmp</filename></entry>
338 <entry><filename class="headerfile">csignal</filename></entry>
339 <entry><filename class="headerfile">cstdarg</filename></entry>
340 <entry><filename class="headerfile">cstdbool</filename></entry>
343 <entry><filename class="headerfile">cstddef</filename></entry>
344 <entry><filename class="headerfile">cstdint</filename></entry>
345 <entry><filename class="headerfile">cstdlib</filename></entry>
346 <entry><filename class="headerfile">cstdio</filename></entry>
347 <entry><filename class="headerfile">cstring</filename></entry>
350 <entry><filename class="headerfile">ctgmath</filename></entry>
351 <entry><filename class="headerfile">ctime</filename></entry>
352 <entry><filename class="headerfile">cuchar</filename></entry>
353 <entry><filename class="headerfile">cwchar</filename></entry>
354 <entry><filename class="headerfile">cwctype</filename></entry>
362 In addition, TR1 includes as:
366 <title>C++ TR 1 Library Headers</title>
368 <tgroup cols="5" align="left" colsep="1" rowsep="1">
369 <colspec colname="c1"/>
370 <colspec colname="c2"/>
371 <colspec colname="c3"/>
372 <colspec colname="c4"/>
373 <colspec colname="c5"/>
377 <entry><filename class="headerfile">tr1/array</filename></entry>
378 <entry><filename class="headerfile">tr1/complex</filename></entry>
379 <entry><filename class="headerfile">tr1/memory</filename></entry>
380 <entry><filename class="headerfile">tr1/functional</filename></entry>
381 <entry><filename class="headerfile">tr1/random</filename></entry>
384 <entry><filename class="headerfile">tr1/regex</filename></entry>
385 <entry><filename class="headerfile">tr1/tuple</filename></entry>
386 <entry><filename class="headerfile">tr1/type_traits</filename></entry>
387 <entry><filename class="headerfile">tr1/unordered_map</filename></entry>
388 <entry><filename class="headerfile">tr1/unordered_set</filename></entry>
391 <entry><filename class="headerfile">tr1/utility</filename></entry>
402 <title>C++ TR 1 Library Headers for C Library Facilities</title>
404 <tgroup cols="5" align="left" colsep="1" rowsep="1">
405 <colspec colname="c1"/>
406 <colspec colname="c2"/>
407 <colspec colname="c3"/>
408 <colspec colname="c4"/>
409 <colspec colname="c5"/>
413 <entry><filename class="headerfile">tr1/ccomplex</filename></entry>
414 <entry><filename class="headerfile">tr1/cfenv</filename></entry>
415 <entry><filename class="headerfile">tr1/cfloat</filename></entry>
416 <entry><filename class="headerfile">tr1/cmath</filename></entry>
417 <entry><filename class="headerfile">tr1/cinttypes</filename></entry>
420 <entry><filename class="headerfile">tr1/climits</filename></entry>
421 <entry><filename class="headerfile">tr1/cstdarg</filename></entry>
422 <entry><filename class="headerfile">tr1/cstdbool</filename></entry>
423 <entry><filename class="headerfile">tr1/cstdint</filename></entry>
424 <entry><filename class="headerfile">tr1/cstdio</filename></entry>
427 <entry><filename class="headerfile">tr1/cstdlib</filename></entry>
428 <entry><filename class="headerfile">tr1/ctgmath</filename></entry>
429 <entry><filename class="headerfile">tr1/ctime</filename></entry>
430 <entry><filename class="headerfile">tr1/cwchar</filename></entry>
431 <entry><filename class="headerfile">tr1/cwctype</filename></entry>
439 <para>Decimal floating-point arithmetic is available if the C++
440 compiler supports scalar decimal floating-point types defined via
441 <code>__attribute__((mode(SD|DD|LD)))</code>.
445 <title>C++ TR 24733 Decimal Floating-Point Header</title>
447 <tgroup cols="1" align="left" colsep="1" rowsep="1">
448 <colspec colname="c1"/>
451 <entry><filename class="headerfile">decimal/decimal</filename></entry>
458 Also included are files for the C++ ABI interface:
462 <title>C++ ABI Headers</title>
464 <tgroup cols="2" align="left" colsep="1" rowsep="1">
465 <colspec colname="c1"/>
466 <colspec colname="c2"/>
468 <row><entry><filename class="headerfile">cxxabi.h</filename></entry><entry><filename class="headerfile">cxxabi_forced.h</filename></entry></row>
474 And a large variety of extensions.
478 <title>Extension Headers</title>
480 <tgroup cols="5" align="left" colsep="1" rowsep="1">
481 <colspec colname="c1"/>
482 <colspec colname="c2"/>
483 <colspec colname="c3"/>
484 <colspec colname="c4"/>
485 <colspec colname="c5"/>
489 <entry><filename class="headerfile">ext/algorithm</filename></entry>
490 <entry><filename class="headerfile">ext/atomicity.h</filename></entry>
491 <entry><filename class="headerfile">ext/array_allocator.h</filename></entry>
492 <entry><filename class="headerfile">ext/bitmap_allocator.h</filename></entry>
493 <entry><filename class="headerfile">ext/cast.h</filename></entry>
496 <entry><filename class="headerfile">ext/codecvt_specializations.h</filename></entry>
497 <entry><filename class="headerfile">ext/concurrence.h</filename></entry>
498 <entry><filename class="headerfile">ext/debug_allocator.h</filename></entry>
499 <entry><filename class="headerfile">ext/enc_filebuf.h</filename></entry>
500 <entry><filename class="headerfile">ext/extptr_allocator.h</filename></entry>
503 <entry><filename class="headerfile">ext/functional</filename></entry>
504 <entry><filename class="headerfile">ext/iterator</filename></entry>
505 <entry><filename class="headerfile">ext/malloc_allocator.h</filename></entry>
506 <entry><filename class="headerfile">ext/memory</filename></entry>
507 <entry><filename class="headerfile">ext/mt_allocator.h</filename></entry>
510 <entry><filename class="headerfile">ext/new_allocator.h</filename></entry>
511 <entry><filename class="headerfile">ext/numeric</filename></entry>
512 <entry><filename class="headerfile">ext/numeric_traits.h</filename></entry>
513 <entry><filename class="headerfile">ext/pb_ds/assoc_container.h</filename></entry>
514 <entry><filename class="headerfile">ext/pb_ds/priority_queue.h</filename></entry>
517 <entry><filename class="headerfile">ext/pod_char_traits.h</filename></entry>
518 <entry><filename class="headerfile">ext/pool_allocator.h</filename></entry>
519 <entry><filename class="headerfile">ext/rb_tree</filename></entry>
520 <entry><filename class="headerfile">ext/rope</filename></entry>
521 <entry><filename class="headerfile">ext/slist</filename></entry>
524 <entry><filename class="headerfile">ext/stdio_filebuf.h</filename></entry>
525 <entry><filename class="headerfile">ext/stdio_sync_filebuf.h</filename></entry>
526 <entry><filename class="headerfile">ext/throw_allocator.h</filename></entry>
527 <entry><filename class="headerfile">ext/typelist.h</filename></entry>
528 <entry><filename class="headerfile">ext/type_traits.h</filename></entry>
531 <entry><filename class="headerfile">ext/vstring.h</filename></entry>
541 <title>Extension Debug Headers</title>
543 <tgroup cols="5" align="left" colsep="1" rowsep="1">
544 <colspec colname="c1"/>
545 <colspec colname="c2"/>
546 <colspec colname="c3"/>
547 <colspec colname="c4"/>
548 <colspec colname="c5"/>
552 <entry><filename class="headerfile">debug/bitset</filename></entry>
553 <entry><filename class="headerfile">debug/deque</filename></entry>
554 <entry><filename class="headerfile">debug/list</filename></entry>
555 <entry><filename class="headerfile">debug/map</filename></entry>
556 <entry><filename class="headerfile">debug/set</filename></entry>
560 <entry><filename class="headerfile">debug/string</filename></entry>
561 <entry><filename class="headerfile">debug/unordered_map</filename></entry>
562 <entry><filename class="headerfile">debug/unordered_set</filename></entry>
563 <entry><filename class="headerfile">debug/vector</filename></entry>
573 <title>Extension Profile Headers</title>
575 <tgroup cols="4" align="left" colsep="1" rowsep="1">
576 <colspec colname="c1"/>
577 <colspec colname="c2"/>
578 <colspec colname="c3"/>
579 <colspec colname="c4"/>
583 <entry><filename class="headerfile">profile/bitset</filename></entry>
584 <entry><filename class="headerfile">profile/deque</filename></entry>
585 <entry><filename class="headerfile">profile/list</filename></entry>
586 <entry><filename class="headerfile">profile/map</filename></entry>
590 <entry><filename class="headerfile">profile/set</filename></entry>
591 <entry><filename class="headerfile">profile/unordered_map</filename></entry>
592 <entry><filename class="headerfile">profile/unordered_set</filename></entry>
593 <entry><filename class="headerfile">profile/vector</filename></entry>
603 <title>Extension Parallel Headers</title>
605 <tgroup cols="2" align="left" colsep="1" rowsep="1">
606 <colspec colname="c1"/>
607 <colspec colname="c2"/>
610 <entry><filename class="headerfile">parallel/algorithm</filename></entry>
611 <entry><filename class="headerfile">parallel/numeric</filename></entry>
619 <section xml:id="manual.intro.using.headers.mixing" xreflabel="Mixing Headers"><info><title>Mixing Headers</title></info>
622 <para> A few simple rules.
625 <para>First, mixing different dialects of the standard headers is not
626 possible. It's an all-or-nothing affair. Thus, code like
630 #include <array>
631 #include <functional>
634 <para>Implies C++11 mode. To use the entities in <array>, the C++11
635 compilation mode must be used, which implies the C++11 functionality
636 (and deprecations) in <functional> will be present.
639 <para>Second, the other headers can be included with either dialect of
640 the standard headers, although features and types specific to C++11
641 are still only enabled when in C++11 compilation mode. So, to use
642 rvalue references with <code>__gnu_cxx::vstring</code>, or to use the
643 debug-mode versions of <code>std::unordered_map</code>, one must use
644 the <code>std=gnu++11</code> compiler flag. (Or <code>std=c++11</code>, of course.)
647 <para>A special case of the second rule is the mixing of TR1 and C++11
648 facilities. It is possible (although not especially prudent) to
649 include both the TR1 version and the C++11 version of header in the
650 same translation unit:
654 #include <tr1/type_traits>
655 #include <type_traits>
658 <para> Several parts of C++11 diverge quite substantially from TR1 predecessors.
662 <section xml:id="manual.intro.using.headers.cheaders" xreflabel="C Headers and"><info><title>The C Headers and <code>namespace std</code></title></info>
666 The standard specifies that if one includes the C-style header
667 (<math.h> in this case), the symbols will be available
668 in the global namespace and perhaps in
669 namespace <code>std::</code> (but this is no longer a firm
670 requirement.) On the other hand, including the C++-style
671 header (<cmath>) guarantees that the entities will be
672 found in namespace std and perhaps in the global namespace.
676 Usage of C++-style headers is recommended, as then
677 C-linkage names can be disambiguated by explicit qualification, such
678 as by <code>std::abort</code>. In addition, the C++-style headers can
679 use function overloading to provide a simpler interface to certain
680 families of C-functions. For instance in <cmath>, the
681 function <code>std::sin</code> has overloads for all the builtin
682 floating-point types. This means that <code>std::sin</code> can be
683 used uniformly, instead of a combination
684 of <code>std::sinf</code>, <code>std::sin</code>,
685 and <code>std::sinl</code>.
689 <section xml:id="manual.intro.using.headers.pre" xreflabel="Precompiled Headers"><info><title>Precompiled Headers</title></info>
693 <para>There are three base header files that are provided. They can be
694 used to precompile the standard headers and extensions into binary
695 files that may the be used to speed compiles that use these headers.
701 <para>stdc++.h</para>
702 <para>Includes all standard headers. Actual content varies depending on
708 <para>stdtr1c++.h</para>
709 <para>Includes all of <stdc++.h>, and adds all the TR1 headers.
713 <listitem><para>extc++.h</para>
714 <para>Includes all of <stdtr1c++.h>, and adds all the Extension headers.
718 <para>How to construct a .gch file from one of these base header files.</para>
720 <para>First, find the include directory for the compiler. One way to do
726 #include <...> search starts here:
727 /mnt/share/bld/H-x86-gcc.20071201/include/c++/4.3.0
733 <para>Then, create a precompiled header file with the same flags that
734 will be used to compile other projects.</para>
737 g++ -Winvalid-pch -x c++-header -g -O2 -o ./stdc++.h.gch /mnt/share/bld/H-x86-gcc.20071201/include/c++/4.3.0/x86_64-unknown-linux-gnu/bits/stdc++.h
740 <para>The resulting file will be quite large: the current size is around
741 thirty megabytes. </para>
743 <para>How to use the resulting file.</para>
746 g++ -I. -include stdc++.h -H -g -O2 hello.cc
749 <para>Verification that the PCH file is being used is easy:</para>
752 g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2 hello.cc -o test.exe
754 . /mnt/share/bld/H-x86-gcc.20071201/include/c++/4.3.0/iostream
755 . /mnt/share/bld/H-x86-gcc.20071201include/c++/4.3.0/string
758 <para>The exclamation point to the left of the <code>stdc++.h.gch</code> listing means that the generated PCH file was used, and thus the </para>
761 <para> Detailed information about creating precompiled header files can be found in the GCC <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html">documentation</link>.
768 <section xml:id="manual.intro.using.macros" xreflabel="Macros"><info><title>Macros</title></info>
769 <?dbhtml filename="using_macros.html"?>
773 All library macros begin with <code>_GLIBCXX_</code>.
777 Furthermore, all pre-processor macros, switches, and
778 configuration options are gathered in the
779 file <filename class="headerfile">c++config.h</filename>, which
780 is generated during the libstdc++ configuration and build
781 process. This file is then included when needed by files part of
782 the public libstdc++ API, like <ios>. Most of these macros
783 should not be used by consumers of libstdc++, and are reserved
784 for internal implementation use. <emphasis>These macros cannot
785 be redefined</emphasis>.
789 A select handful of macros control libstdc++ extensions and extra
790 features, or provide versioning information for the API. Only
791 those macros listed below are offered for consideration by the
795 <para>Below is the macro which users may check for library version
800 <term><code>__GLIBCXX__</code></term>
802 <para>The current version of
803 libstdc++ in compressed ISO date format, form of an unsigned
804 long. For details on the value of this particular macro for a
805 particular release, please consult this <link linkend="appendix.porting.abi">
812 <para>Below are the macros which users may change with #define/#undef or
813 with -D/-U compiler flags. The default state of the symbol is
816 <para><quote>Configurable</quote> (or <quote>Not configurable</quote>) means
817 that the symbol is initially chosen (or not) based on
818 --enable/--disable options at library build and configure time
819 (documented <link linkend="manual.intro.setup.configure">here</link>), with the
820 various --enable/--disable choices being translated to
824 <para> <acronym>ABI</acronym> means that changing from the default value may
825 mean changing the <acronym>ABI</acronym> of compiled code. In other words, these
826 choices control code which has already been compiled (i.e., in a
827 binary such as libstdc++.a/.so). If you explicitly #define or
828 #undef these macros, the <emphasis>headers</emphasis> may see different code
829 paths, but the <emphasis>libraries</emphasis> which you link against will not.
830 Experimenting with different values with the expectation of
831 consistent linkage requires changing the config headers before
832 building/installing the library.
836 <varlistentry><term><code>_GLIBCXX_USE_DEPRECATED</code></term>
839 Defined by default. Not configurable. ABI-changing. Turning this off
840 removes older ARM-style iostreams code, and other anachronisms
841 from the API. This macro is dependent on the version of the
842 standard being tracked, and as a result may give different results for
843 <code>-std=c++98</code> and <code>-std=c++11</code>. This may
844 be useful in updating old C++ code which no longer meet the
845 requirements of the language, or for checking current code
846 against new language standards.
848 </listitem></varlistentry>
850 <varlistentry><term><code>_GLIBCXX_FORCE_NEW</code></term>
853 Undefined by default. When defined, memory allocation and
854 allocators controlled by libstdc++ call operator new/delete
855 without caching and pooling. Configurable via
856 <code>--enable-libstdcxx-allocator</code>. ABI-changing.
858 </listitem></varlistentry>
861 <varlistentry><term><code>_GLIBCXX_CONCEPT_CHECKS</code></term>
864 Undefined by default. Configurable via
865 <code>--enable-concept-checks</code>. When defined, performs
866 compile-time checking on certain template instantiations to
867 detect violations of the requirements of the standard. This
868 is described in more detail <link linkend="manual.ext.compile_checks">here</link>.
870 </listitem></varlistentry>
872 <varlistentry><term><code>_GLIBCXX_DEBUG</code></term>
875 Undefined by default. When defined, compiles user code using
876 the <link linkend="manual.ext.debug_mode">debug mode</link>.
878 </listitem></varlistentry>
879 <varlistentry><term><code>_GLIBCXX_DEBUG_PEDANTIC</code></term>
882 Undefined by default. When defined while compiling with
883 the <link linkend="manual.ext.debug_mode">debug mode</link>, makes
884 the debug mode extremely picky by making the use of libstdc++
885 extensions and libstdc++-specific behavior into errors.
887 </listitem></varlistentry>
888 <varlistentry><term><code>_GLIBCXX_PARALLEL</code></term>
890 <para>Undefined by default. When defined, compiles user code
891 using the <link linkend="manual.ext.parallel_mode">parallel
894 </listitem></varlistentry>
896 <varlistentry><term><code>_GLIBCXX_PROFILE</code></term>
898 <para>Undefined by default. When defined, compiles user code
899 using the <link linkend="manual.ext.profile_mode">profile
902 </listitem></varlistentry>
907 <section xml:id="manual.intro.using.namespaces" xreflabel="Namespaces"><info><title>Namespaces</title></info>
908 <?dbhtml filename="using_namespaces.html"?>
911 <section xml:id="manual.intro.using.namespaces.all" xreflabel="Available Namespaces"><info><title>Available Namespaces</title></info>
916 <para> There are three main namespaces.
920 <listitem><para>std</para>
921 <para>The ISO C++ standards specify that "all library entities are defined
922 within namespace std." This includes namespaces nested
923 within <code>namespace std</code>, such as <code>namespace
927 <listitem><para>abi</para>
928 <para>Specified by the C++ ABI. This ABI specifies a number of type and
929 function APIs supplemental to those required by the ISO C++ Standard,
930 but necessary for interoperability.
934 <listitem><para>__gnu_</para>
935 <para>Indicating one of several GNU extensions. Choices
936 include <code>__gnu_cxx</code>, <code>__gnu_debug</code>, <code>__gnu_parallel</code>,
937 and <code>__gnu_pbds</code>.
941 <para> A complete list of implementation namespaces (including namespace contents) is available in the generated source <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/namespaces.html">documentation</link>.
947 <section xml:id="manual.intro.using.namespaces.std" xreflabel="namespace std"><info><title>namespace std</title></info>
952 One standard requirement is that the library components are defined
953 in <code>namespace std::</code>. Thus, in order to use these types or
954 functions, one must do one of two things:
958 <listitem><para>put a kind of <emphasis>using-declaration</emphasis> in your source
959 (either <code>using namespace std;</code> or i.e. <code>using
960 std::string;</code>) This approach works well for individual source files, but
961 should not be used in a global context, like header files.
962 </para></listitem> <listitem><para>use a <emphasis>fully
963 qualified name</emphasis> for each library symbol
964 (i.e. <code>std::string</code>, <code>std::cout</code>) Always can be
965 used, and usually enhanced, by strategic use of typedefs. (In the
966 cases where the qualified verbiage becomes unwieldy.)
973 <section xml:id="manual.intro.using.namespaces.comp" xreflabel="Using Namespace Composition"><info><title>Using Namespace Composition</title></info>
977 Best practice in programming suggests sequestering new data or
978 functionality in a sanely-named, unique namespace whenever
979 possible. This is considered an advantage over dumping everything in
980 the global namespace, as then name look-up can be explicitly enabled or
981 disabled as above, symbols are consistently mangled without repetitive
982 naming prefixes or macros, etc.
985 <para>For instance, consider a project that defines most of its classes in <code>namespace gtk</code>. It is possible to
986 adapt <code>namespace gtk</code> to <code>namespace std</code> by using a C++-feature called
987 <emphasis>namespace composition</emphasis>. This is what happens if
988 a <emphasis>using</emphasis>-declaration is put into a
989 namespace-definition: the imported symbol(s) gets imported into the
990 currently active namespace(s). For example:
996 using std::tr1::array;
998 class Window { ... };
1002 In this example, <code>std::string</code> gets imported into
1003 <code>namespace gtk</code>. The result is that use of
1004 <code>std::string</code> inside namespace gtk can just use <code>string</code>, without the explicit qualification.
1006 <code>std::string</code> does not get imported into
1007 the global namespace. Additionally, a more elaborate arrangement can be made for backwards compatibility and portability, whereby the
1008 <code>using</code>-declarations can wrapped in macros that
1009 are set based on autoconf-tests to either "" or i.e. <code>using
1010 std::string;</code> (depending on whether the system has
1011 libstdc++ in <code>std::</code> or not). (ideas from
1012 Llewelly and Karl Nelson)
1019 <section xml:id="manual.intro.using.linkage" xreflabel="Linkage"><info><title>Linking</title></info>
1020 <?dbhtml filename="using_dynamic_or_shared.html"?>
1023 <section xml:id="manual.intro.using.linkage.freestanding" xreflabel="Freestanding"><info><title>Almost Nothing</title></info>
1026 Or as close as it gets: freestanding. This is a minimal
1027 configuration, with only partial support for the standard
1028 library. Assume only the following header files can be used:
1034 <filename class="headerfile">cstdarg</filename>
1040 <filename class="headerfile">cstddef</filename>
1046 <filename class="headerfile">cstdlib</filename>
1052 <filename class="headerfile">exception</filename>
1058 <filename class="headerfile">limits</filename>
1064 <filename class="headerfile">new</filename>
1070 <filename class="headerfile">exception</filename>
1076 <filename class="headerfile">typeinfo</filename>
1082 In addition, throw in
1088 <filename class="headerfile">cxxabi.h</filename>.
1095 C++11 <link linkend="manual.intro.using.flags">dialect</link> add
1101 <filename class="headerfile">initializer_list</filename>
1106 <filename class="headerfile">type_traits</filename>
1111 <para> There exists a library that offers runtime support for
1112 just these headers, and it is called
1113 <filename class="libraryfile">libsupc++.a</filename>. To use it, compile with <command>gcc</command> instead of <command>g++</command>, like so:
1117 <command>gcc foo.cc -lsupc++</command>
1121 No attempt is made to verify that only the minimal subset
1122 identified above is actually used at compile time. Violations
1123 are diagnosed as undefined symbols at link time.
1127 <section xml:id="manual.intro.using.linkage.dynamic" xreflabel="Dynamic and Shared"><info><title>Finding Dynamic or Shared Libraries</title></info>
1131 If the only library built is the static library
1132 (<filename class="libraryfile">libstdc++.a</filename>), or if
1133 specifying static linking, this section is can be skipped. But
1134 if building or using a shared library
1135 (<filename class="libraryfile">libstdc++.so</filename>), then
1136 additional location information will need to be provided.
1142 A quick read of the relevant part of the GCC
1143 manual, <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/gcc/Invoking-G_002b_002b.html#Invoking-G_002b_002b">Compiling
1144 C++ Programs</link>, specifies linking against a C++
1145 library. More details from the
1146 GCC <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/faq.html#rpath">FAQ</link>,
1147 which states <emphasis>GCC does not, by default, specify a
1148 location so that the dynamic linker can find dynamic libraries at
1152 Users will have to provide this information.
1155 Methods vary for different platforms and different styles, and
1156 are printed to the screen during installation. To summarize:
1161 At runtime set <literal>LD_LIBRARY_PATH</literal> in your
1162 environment correctly, so that the shared library for
1163 libstdc++ can be found and loaded. Be certain that you
1164 understand all of the other implications and behavior
1165 of <literal>LD_LIBRARY_PATH</literal> first.
1171 Compile the path to find the library at runtime into the
1172 program. This can be done by passing certain options to
1173 <command>g++</command>, which will in turn pass them on to
1174 the linker. The exact format of the options is dependent on
1175 which linker you use:
1180 GNU ld (default on GNU/Linux):
1181 <literal>-Wl,-rpath,</literal><filename class="directory">destdir/lib</filename>
1187 <literal>-Wl,-rpath,</literal><filename class="directory">destdir/lib</filename>
1193 <literal>-Wl,-R</literal><filename class="directory">destdir/lib</filename>
1200 Some linkers allow you to specify the path to the library by
1201 setting <literal>LD_RUN_PATH</literal> in your environment
1207 On some platforms the system administrator can configure the
1208 dynamic linker to always look for libraries in
1209 <filename class="directory">destdir/lib</filename>, for example
1210 by using the <command>ldconfig</command> utility on GNU/Linux
1211 or the <command>crle</command> utility on Solaris. This is a
1212 system-wide change which can make the system unusable so if you
1213 are unsure then use one of the other methods described above.
1218 Use the <command>ldd</command> utility on the linked executable
1220 which <filename class="libraryfile">libstdc++.so</filename>
1221 library the system will get at runtime.
1224 A <filename class="libraryfile">libstdc++.la</filename> file is
1225 also installed, for use with Libtool. If you use Libtool to
1226 create your executables, these details are taken care of for
1233 <section xml:id="manual.intro.using.concurrency" xreflabel="Concurrency"><info><title>Concurrency</title></info>
1234 <?dbhtml filename="using_concurrency.html"?>
1237 <para>This section discusses issues surrounding the proper compilation
1238 of multithreaded applications which use the Standard C++
1239 library. This information is GCC-specific since the C++
1240 standard does not address matters of multithreaded applications.
1243 <section xml:id="manual.intro.using.concurrency.prereq" xreflabel="Thread Prereq"><info><title>Prerequisites</title></info>
1246 <para>All normal disclaimers aside, multithreaded C++ application are
1247 only supported when libstdc++ and all user code was built with
1248 compilers which report (via <code> gcc/g++ -v </code>) the same thread
1249 model and that model is not <emphasis>single</emphasis>. As long as your
1250 final application is actually single-threaded, then it should be
1251 safe to mix user code built with a thread model of
1252 <emphasis>single</emphasis> with a libstdc++ and other C++ libraries built
1253 with another thread model useful on the platform. Other mixes
1254 may or may not work but are not considered supported. (Thus, if
1255 you distribute a shared C++ library in binary form only, it may
1256 be best to compile it with a GCC configured with
1257 --enable-threads for maximal interchangeability and usefulness
1258 with a user population that may have built GCC with either
1259 --enable-threads or --disable-threads.)
1261 <para>When you link a multithreaded application, you will probably
1262 need to add a library or flag to g++. This is a very
1263 non-standardized area of GCC across ports. Some ports support a
1264 special flag (the spelling isn't even standardized yet) to add
1265 all required macros to a compilation (if any such flags are
1266 required then you must provide the flag for all compilations not
1267 just linking) and link-library additions and/or replacements at
1268 link time. The documentation is weak. Here is a quick summary
1269 to display how ad hoc this is: On Solaris, both -pthreads and
1270 -threads (with subtly different meanings) are honored. On OSF,
1271 -pthread and -threads (with subtly different meanings) are
1272 honored. On GNU/Linux x86, -pthread is honored. On FreeBSD,
1273 -pthread is honored. Some other ports use other switches.
1274 AFAIK, none of this is properly documented anywhere other than
1275 in ``gcc -dumpspecs'' (look at lib and cpp entries).
1280 <section xml:id="manual.intro.using.concurrency.thread_safety" xreflabel="Thread Safety"><info><title>Thread Safety</title></info>
1284 In the terms of the 2011 C++ standard a thread-safe program is one which
1285 does not perform any conflicting non-atomic operations on memory locations
1286 and so does not contain any data races.
1287 The standard places requirements on the library to ensure that no data
1288 races are caused by the library itself or by programs which use the
1289 library correctly (as described below).
1290 The C++11 memory model and library requirements are a more formal version
1291 of the <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.sgi.com/tech/stl/thread_safety.html">SGI STL</link> definition of thread safety, which the library used
1292 prior to the 2011 standard.
1296 <para>The library strives to be thread-safe when all of the following
1301 <para>The system's libc is itself thread-safe,
1306 The compiler in use reports a thread model other than
1307 'single'. This can be tested via output from <code>gcc
1308 -v</code>. Multi-thread capable versions of gcc output
1309 something like this:
1313 Using built-in specs.
1316 gcc version 4.1.2 20070925 (Red Hat 4.1.2-33)
1319 <para>Look for "Thread model" lines that aren't equal to "single."</para>
1323 Requisite command-line flags are used for atomic operations
1324 and threading. Examples of this include <code>-pthread</code>
1325 and <code>-march=native</code>, although specifics vary
1326 depending on the host environment. See <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/gcc/Option-Summary.html">Machine
1327 Dependent Options</link>.
1332 An implementation of atomicity.h functions
1333 exists for the architecture in question. See the internals documentation for more <link linkend="internals.thread_safety">details</link>.
1339 <para>The user code must guard against concurrent function calls which
1340 access any particular library object's state when one or more of
1341 those accesses modifies the state. An object will be modified by
1342 invoking a non-const member function on it or passing it as a
1343 non-const argument to a library function. An object will not be
1344 modified by invoking a const member function on it or passing it to
1345 a function as a pointer- or reference-to-const.
1346 Typically, the application
1347 programmer may infer what object locks must be held based on the
1348 objects referenced in a function call and whether the objects are
1349 accessed as const or non-const. Without getting
1350 into great detail, here is an example which requires user-level
1354 library_class_a shared_object_a;
1356 void thread_main () {
1357 library_class_b *object_b = new library_class_b;
1358 shared_object_a.add_b (object_b); // must hold lock for shared_object_a
1359 shared_object_a.mutate (); // must hold lock for shared_object_a
1362 // Multiple copies of thread_main() are started in independent threads.</programlisting>
1363 <para>Under the assumption that object_a and object_b are never exposed to
1364 another thread, here is an example that does not require any
1368 void thread_main () {
1369 library_class_a object_a;
1370 library_class_b *object_b = new library_class_b;
1371 object_a.add_b (object_b);
1375 <para>All library types are safe to use in a multithreaded program
1376 if objects are not shared between threads or as
1377 long each thread carefully locks out access by any other
1378 thread while it modifies any object visible to another thread.
1379 Unless otherwise documented, the only exceptions to these rules
1380 are atomic operations on the types in
1381 <filename class="headerfile"><atomic></filename>
1382 and lock/unlock operations on the standard mutex types in
1383 <filename class="headerfile"><mutex></filename>. These
1384 atomic operations allow concurrent accesses to the same object
1385 without introducing data races.
1388 <para>The following member functions of standard containers can be
1389 considered to be const for the purposes of avoiding data races:
1390 <code>begin</code>, <code>end</code>, <code>rbegin</code>, <code>rend</code>,
1391 <code>front</code>, <code>back</code>, <code>data</code>,
1392 <code>find</code>, <code>lower_bound</code>, <code>upper_bound</code>,
1393 <code>equal_range</code>, <code>at</code>
1394 and, except in associative or unordered associative containers,
1395 <code>operator[]</code>. In other words, although they are non-const
1396 so that they can return mutable iterators, those member functions
1397 will not modify the container.
1398 Accessing an iterator might cause a non-modifying access to
1399 the container the iterator refers to (for example incrementing a
1400 list iterator must access the pointers between nodes, which are part
1401 of the container and so conflict with other accesses to the container).
1404 <para>Programs which follow the rules above will not encounter data
1405 races in library code, even when using library types which share
1406 state between distinct objects. In the example below the
1407 <code>shared_ptr</code> objects share a reference count, but
1408 because the code does not perform any non-const operations on the
1409 globally-visible object, the library ensures that the reference
1410 count updates are atomic and do not introduce data races:
1413 std::shared_ptr<int> global_sp;
1415 void thread_main() {
1416 auto local_sp = global_sp; // OK, copy constructor's parameter is reference-to-const
1418 int i = *global_sp; // OK, operator* is const
1419 int j = *local_sp; // OK, does not operate on global_sp
1421 // *global_sp = 2; // NOT OK, modifies int visible to other threads
1422 // *local_sp = 2; // NOT OK, modifies int visible to other threads
1424 // global_sp.reset(); // NOT OK, reset is non-const
1425 local_sp.reset(); // OK, does not operate on global_sp
1429 global_sp.reset(new int(1));
1430 std::thread t1(thread_main);
1431 std::thread t2(thread_main);
1437 <para>For further details of the C++11 memory model see Hans-J. Boehm's
1438 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/user-faq.html">Threads
1439 and memory model for C++</link> pages, particularly the <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/threadsintro.html">introduction</link>
1440 and <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/user-faq.html">FAQ</link>.
1444 <section xml:id="manual.intro.using.concurrency.atomics" xreflabel="Atomics"><info><title>Atomics</title></info>
1450 <section xml:id="manual.intro.using.concurrency.io" xreflabel="IO"><info><title>IO</title></info>
1452 <para>This gets a bit tricky. Please read carefully, and bear with me.
1455 <section xml:id="concurrency.io.structure" xreflabel="Structure"><info><title>Structure</title></info>
1458 type called <code>__basic_file</code> provides our abstraction layer
1459 for the <code>std::filebuf</code> classes. Nearly all decisions dealing
1460 with actual input and output must be made in <code>__basic_file</code>.
1462 <para>A generic locking mechanism is somewhat in place at the filebuf layer,
1463 but is not used in the current code. Providing locking at any higher
1464 level is akin to providing locking within containers, and is not done
1465 for the same reasons (see the links above).
1469 <section xml:id="concurrency.io.defaults" xreflabel="Defaults"><info><title>Defaults</title></info>
1471 <para>The __basic_file type is simply a collection of small wrappers around
1472 the C stdio layer (again, see the link under Structure). We do no
1473 locking ourselves, but simply pass through to calls to <code>fopen</code>,
1474 <code>fwrite</code>, and so forth.
1476 <para>So, for 3.0, the question of "is multithreading safe for I/O"
1477 must be answered with, "is your platform's C library threadsafe
1478 for I/O?" Some are by default, some are not; many offer multiple
1479 implementations of the C library with varying tradeoffs of threadsafety
1480 and efficiency. You, the programmer, are always required to take care
1481 with multiple threads.
1483 <para>(As an example, the POSIX standard requires that C stdio FILE*
1484 operations are atomic. POSIX-conforming C libraries (e.g, on Solaris
1485 and GNU/Linux) have an internal mutex to serialize operations on
1486 FILE*s. However, you still need to not do stupid things like calling
1487 <code>fclose(fs)</code> in one thread followed by an access of
1488 <code>fs</code> in another.)
1490 <para>So, if your platform's C library is threadsafe, then your
1491 <code>fstream</code> I/O operations will be threadsafe at the lowest
1492 level. For higher-level operations, such as manipulating the data
1493 contained in the stream formatting classes (e.g., setting up callbacks
1494 inside an <code>std::ofstream</code>), you need to guard such accesses
1495 like any other critical shared resource.
1499 <section xml:id="concurrency.io.future" xreflabel="Future"><info><title>Future</title></info>
1502 second choice may be available for I/O implementations: libio. This is
1503 disabled by default, and in fact will not currently work due to other
1504 issues. It will be revisited, however.
1506 <para>The libio code is a subset of the guts of the GNU libc (glibc) I/O
1507 implementation. When libio is in use, the <code>__basic_file</code>
1508 type is basically derived from FILE. (The real situation is more
1509 complex than that... it's derived from an internal type used to
1510 implement FILE. See libio/libioP.h to see scary things done with
1511 vtbls.) The result is that there is no "layer" of C stdio
1512 to go through; the filebuf makes calls directly into the same
1513 functions used to implement <code>fread</code>, <code>fwrite</code>,
1514 and so forth, using internal data structures. (And when I say
1515 "makes calls directly," I mean the function is literally
1516 replaced by a jump into an internal function. Fast but frightening.
1519 <para>Also, the libio internal locks are used. This requires pulling in
1520 large chunks of glibc, such as a pthreads implementation, and is one
1521 of the issues preventing widespread use of libio as the libstdc++
1522 cstdio implementation.
1524 <para>But we plan to make this work, at least as an option if not a future
1525 default. Platforms running a copy of glibc with a recent-enough
1526 version will see calls from libstdc++ directly into the glibc already
1527 installed. For other platforms, a copy of the libio subsection will
1528 be built and included in libstdc++.
1532 <section xml:id="concurrency.io.alt" xreflabel="Alt"><info><title>Alternatives</title></info>
1534 <para>Don't forget that other cstdio implementations are possible. You could
1535 easily write one to perform your own forms of locking, to solve your
1536 "interesting" problems.
1542 <section xml:id="manual.intro.using.concurrency.containers" xreflabel="Containers"><info><title>Containers</title></info>
1545 <para>This section discusses issues surrounding the design of
1546 multithreaded applications which use Standard C++ containers.
1547 All information in this section is current as of the gcc 3.0
1548 release and all later point releases. Although earlier gcc
1549 releases had a different approach to threading configuration and
1550 proper compilation, the basic code design rules presented here
1551 were similar. For information on all other aspects of
1552 multithreading as it relates to libstdc++, including details on
1553 the proper compilation of threaded code (and compatibility between
1554 threaded and non-threaded code), see Chapter 17.
1556 <para>Two excellent pages to read when working with the Standard C++
1557 containers and threads are
1558 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.sgi.com/tech/stl/thread_safety.html">SGI's
1559 http://www.sgi.com/tech/stl/thread_safety.html</link> and
1560 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.sgi.com/tech/stl/Allocators.html">SGI's
1561 http://www.sgi.com/tech/stl/Allocators.html</link>.
1563 <para><emphasis>However, please ignore all discussions about the user-level
1564 configuration of the lock implementation inside the STL
1565 container-memory allocator on those pages. For the sake of this
1566 discussion, libstdc++ configures the SGI STL implementation,
1567 not you. This is quite different from how gcc pre-3.0 worked.
1568 In particular, past advice was for people using g++ to
1569 explicitly define _PTHREADS or other macros or port-specific
1570 compilation options on the command line to get a thread-safe
1571 STL. This is no longer required for any port and should no
1572 longer be done unless you really know what you are doing and
1573 assume all responsibility.</emphasis>
1575 <para>Since the container implementation of libstdc++ uses the SGI
1576 code, we use the same definition of thread safety as SGI when
1577 discussing design. A key point that beginners may miss is the
1578 fourth major paragraph of the first page mentioned above
1579 (<emphasis>For most clients...</emphasis>), which points out that
1580 locking must nearly always be done outside the container, by
1581 client code (that'd be you, not us). There is a notable
1582 exceptions to this rule. Allocators called while a container or
1583 element is constructed uses an internal lock obtained and
1584 released solely within libstdc++ code (in fact, this is the
1585 reason STL requires any knowledge of the thread configuration).
1587 <para>For implementing a container which does its own locking, it is
1588 trivial to provide a wrapper class which obtains the lock (as
1589 SGI suggests), performs the container operation, and then
1590 releases the lock. This could be templatized <emphasis>to a certain
1591 extent</emphasis>, on the underlying container and/or a locking
1592 mechanism. Trying to provide a catch-all general template
1593 solution would probably be more trouble than it's worth.
1595 <para>The library implementation may be configured to use the
1596 high-speed caching memory allocator, which complicates thread
1597 safety issues. For all details about how to globally override
1598 this at application run-time
1599 see <link linkend="manual.intro.using.macros">here</link>. Also
1601 on <link linkend="std.util.memory.allocator">allocator</link>
1602 options and capabilities.
1608 <!-- Section 0x : Exception policies, expectations, topics -->
1609 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="xml" href="using_exceptions.xml">
1612 <!-- Section 0x : Debug -->
1613 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="xml" href="debug.xml">