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	9	<p align="left"><img src="../../boost.png" alt="Boost" width="277" height="86"></p>
	10	<h1 align="center">Boost Configuration Reference</h1>
	11	<h2>Contents</h2>
	12	<pre><a href="#configuring">Configuring Boost for Your Platform</a>
	13	<a href="#default_config">Using the default boost configuration
	14	</a> <a href="#header">The <boost\config.hpp> header</a>
	15	<a href="#config_script">Using the configure script</a>
	16	<a href="#user_settable">User settable options</a>
	17	<a href="#advanced_config">Advanced configuration usage</a>
	18	<a href="#testing">Testing the boost configuration</a>
	19	<a href="#macro_ref">Boost Macro Reference</a>
	20	<a href="#defects">Macros that describe defects</a>
	21	<a href="#features">Macros that describe optional features</a>
	22	<a href="#helpers">Boost Helper Macros</a>
	23	<a href="#info_macros">Boost Informational Macros</a>
	24	<a href="#source">Macros for libraries with separate source code</a>
	25	<a href="#guidelines">Guidelines for Boost Authors</a>
	26	<a href="#defect_guidelines">Adding New Defect Macros</a>
	27	<a href="#feature_guidelines">Adding New Feature Test Macros</a>
	28	<a href="#modify_guidelines">Modifying the Boost Configuration Headers</a>
	29	<a href="#rationale">Rationale</a>
	30	<a href="#Acknowledgements">Acknowledgements</a></pre>
	31	<h2><a name="configuring"></a>Configuring Boost for Your Platform</h2>
	32	<h4><a name="default_config"></a>Using the default boost configuration</h4>
	33	<p>Boost is comes already configured for most common compilers and platforms; you
	34	should be able to use boost "as is". Since the compiler is configured
	35	separately from the standard library, the default configuration should work
	36	even if you replace the compiler's standard library with a third-party standard
	37	library (like <a href="http://www.stlport.org">STLport</a>).
	38	</p>
	39	<p>Using boost "as is" without trying to reconfigure is the recommended method for
	40	using boost. You can, however, run the configure script if you want to, and
	41	there are regression tests provided that allow you to test the current boost
	42	configuration with your particular compiler setup.</p>
	43	<p>Boost library users can request support for additional compilers or platforms
	44	by visiting our <a href="http://sourceforge.net/tracker/?group_id=7586">Tracker</a>
	45	and submitting a support request.
	46	</p>
	47	<h4>The <a href="../../boost/config.hpp"><boost/config.hpp></a> <a name="header">
	48	header</a></h4>
	49	<p>Boost library implementations access configuration macros via <code>#include
	50	<boost/config.hpp></code>.
	51	</p>
	52	<P>While Boost library users are not required to include that file directly, or
	53	use those configuration macros, such use is acceptable.  The configuration
	54	macros are documented as to their purpose, usage, and limitations which makes
	55	them usable by both Boost library and user code.
	56	</P>
	57	<P>Boost <A href="#info_macros">informational</A> or <A href="#helpers">helper</A>
	58	macros are designed for use by Boost users as well as for our own internal
	59	use.  Note however, that the <A href="#features">feature test</A> and <A href="#defects">
	60	defect test</A> macros were designed for internal use by Boost libraries,
	61	not user code, so they can change at any time (though no gratuitous changes are
	62	made to them). Boost library problems resulting from changes to the
	63	configuration macros are caught by the Boost regression tests, so the Boost
	64	libraries are updated to account for those changes. By contrast, Boost library
	65	user code can be adversely affected by changes to the macros without warning.
	66	The best way to keep abreast of changes to the macros used in user code is to
	67	monitor the discussions on the Boost developers list.</P>
	68	<h4><a name="config_script">Using the configure script</a></h4>
	69	<p>If you know that boost is incorrectly configured for your particular setup, and
	70	you are on a UNIX like platform, then you may want to try and improve things by
	71	running the boost configure script. From a shell command prompt you will need
	72	to cd into <boost-root>/libs/config/ and type:</p>
	73	<pre>sh ./configure</pre>
	74	<p>you will see a list of the items being checked as the script works it way
	75	through the regression tests. Note that the configure script only really
	76	auto-detects your compiler if it's called g++, c++ or CC. If you are using some
	77	other compiler then you will need to set one or more of the following
	78	environment variables:</p>
	79	<table border="1" cellpadding="7" cellspacing="1" width="624">
	80	<tr>
	81	<td valign="top" width="50%"><p align="center"><b>Variable</b></p>
	82	</td>
	83	<td valign="top" width="50%"><p align="center"><b>Description</b></p>
	84	</td>
	85	</tr>
	86	<tr>
	87	<td valign="top" width="50%">CXX</td>
	88	<td valign="top" width="50%">The name of the compiler, for example "c++".</td>
	89	</tr>
	90	<tr>
	91	<td valign="top" width="50%">CXXFLAGS</td>
	92	<td valign="top" width="50%">The compiler flags to use, for example "-O2".</td>
	93	</tr>
	94	<tr>
	95	<td valign="top" width="50%">LDFLAGS</td>
	96	<td valign="top" width="50%">The linker flags to use, for example "-L/mypath".</td>
	97	</tr>
	98	<tr>
	99	<td valign="top" width="50%">LIBS</td>
	100	<td valign="top" width="50%">Any libraries to link in, for example -lpthread.</td>
	101	</tr>
	102	</table>
	103	<p>For example to run the configure script with HP aCC, you might use something
	104	like:</p>
	105	<pre>export CXX="aCC"
	106	export CXXFLAGS="-Aa
	107	-DAportable -D__HPACC_THREAD_SAFE_RB_TREE -DRWSTD_MULTI_THREAD -DRW_MULTI_THREAD -D_REENTRANT -D_THREAD_SAFE" export LDFLAGS="-DAportable"
	108	export LIBS=
	109	"-lpthread" sh
	110	./configure</pre>
	111	<p>However you run the configure script, when it finishes you will find a new
	112	header - user.hpp - located in the <boost-root/libs/config/> directory. <b><i>Note
	113	that configure does not install this header into your boost include path by
	114	default.</i></b> This header contains all the options generated by the
	115	configure script, plus a header-section that contains the user settable options
	116	from the default version of <a href="../../boost/config/user.hpp">user.hpp</a> (located
	117	under <boost-root>/boost/config/). There are two ways you can use this
	118	header:</p>
	119	<p>Option 1: copy the header into <boost-root>/boost/config/ so that it
	120	replaces the default <a href="../../boost/config/user.hpp">user.hpp</a> provided
	121	by boost. This option allows only one configure-generated setup; boost
	122	developers should avoid this option, as it incurs the danger of accidentally
	123	committing a configure-modified user.hpp to the cvs repository (something you
	124	will not be thanked for!).</p>
	125	<p>Option 2: give the header a more memorable name, and place it somewhere
	126	convenient, then define the macro BOOST_USER_CONFIG to point to it. For example
	127	create a new sub-directory <boost-root>/boost/config/user/, and copy the
	128	header there; for example as "multithread-gcc-config.hpp". Then when compiling
	129	add the command line option:
	130	-DBOOST_USER_CONFIG="boost/config/user/multithread-gcc-config.hpp", and boost
	131	will use the new configuration header. This option allows you to generate more
	132	than one configuration header, and to keep them separate from the boost source
	133	- so that updates to the source do not interfere with your configuration.</p>
	134	<h4><a name="user_settable"></a>User settable options</h4>
	135	<p>There are some configuration-options that represent user choices, rather than
	136	compiler defects or platform specific options. These are listed in
	137	<boost/config/user.hpp> and at the start of a configure-generated
	138	user.hpp header. You can define these on the command line, or by editing
	139	<boost/config/user.hpp>, they are listed in the following table: </p>
	140	<table border="1" cellpadding="7" cellspacing="1" width="100%">
	141	<tr>
	142	<td valign="top" width="48%"><p align="center"><b>Macro</b></p>
	143	</td>
	144	<td valign="top" width="52%"><p align="center"><b>Description</b></p>
	145	</td>
	146	</tr>
	147	<tr>
	148	<td valign="top" width="48%">BOOST_USER_CONFIG</td>
	149	<td valign="top" width="52%">When defined, it should point to the name of the user
	150	configuration file to include prior to any boost configuration files. When not
	151	defined, defaults to <<a href="../../boost/config/user.hpp">boost/config/user.hpp</a>>.</td>
	152	</tr>
	153	<tr>
	154	<td valign="top" width="48%">BOOST_COMPILER_CONFIG</td>
	155	<td valign="top" width="52%">When defined, it should point to the name of the
	156	compiler configuration file to use. Defining this cuts out the compiler
	157	selection logic, and eliminates the dependency on the header containing that
	158	logic. For example if you are using gcc, then you could define
	159	BOOST_COMPILER_CONFIG to "<a href="../../boost/config/compiler/gcc.hpp">boost/config/compiler/gcc.hpp</a>".</td>
	160	</tr>
	161	<tr>
	162	<td valign="top" width="48%">BOOST_STDLIB_CONFIG</td>
	163	<td valign="top" width="52%">When defined, it should point to the name of the
	164	standard library configuration file to use. Defining this cuts out the standard
	165	library selection logic, and eliminates the dependency on the header containing
	166	that logic. For example if you are using STLport, then you could define
	167	BOOST_STDLIB_CONFIG to "<a href="../../boost/config/stdlib/stlport.hpp">boost/config/stdlib/stlport.hpp</a>".</td>
	168	</tr>
	169	<tr>
	170	<td valign="top" width="48%">BOOST_PLATFORM_CONFIG</td>
	171	<td valign="top" width="52%">When defined, it should point to the name of the
	172	platform configuration file to use. Defining this cuts out the platform
	173	selection logic, and eliminates the dependency on the header containing that
	174	logic. For example if you are compiling on linux, then you could define
	175	BOOST_PLATFORM_CONFIG to "<a href="../../boost/config/platform/linux.hpp">boost/config/platform/linux.hpp</a>".</td>
	176	</tr>
	177	<tr>
	178	<td valign="top" width="48%">BOOST_NO_COMPILER_CONFIG</td>
	179	<td valign="top" width="52%">When defined, no compiler configuration file is
	180	selected or included, define when the compiler is fully conformant with the
	181	standard, or where the user header (see BOOST_USER_CONFIG), has had any options
	182	necessary added to it, for example by an autoconf generated configure script.</td>
	183	</tr>
	184	<tr>
	185	<td valign="top" width="48%">BOOST_NO_STDLIB_CONFIG</td>
	186	<td valign="top" width="52%">When defined, no standard library configuration file
	187	is selected or included, define when the standard library is fully conformant
	188	with the standard, or where the user header (see BOOST_USER_CONFIG), has had
	189	any options necessary added to it, for example by an autoconf generated
	190	configure script.</td>
	191	</tr>
	192	<tr>
	193	<td valign="top" width="48%">BOOST_NO_PLATFORM_CONFIG</td>
	194	<td valign="top" width="52%">When defined, no platform configuration file is
	195	selected or included, define when the platform is fully conformant with the
	196	standard (and has no useful extra features), or where the user header (see
	197	BOOST_USER_CONFIG), has had any options necessary added to it, for example by
	198	an autoconf generated configure script.</td>
	199	</tr>
	200	<tr>
	201	<td valign="top" width="48%">BOOST_NO_CONFIG</td>
	202	<td valign="top" width="52%">Equivalent to defining all of
	203	BOOST_NO_COMPILER_CONFIG, BOOST_NO_STDLIB_CONFIG and BOOST_NO_PLATFORM_CONFIG.</td>
	204	</tr>
	205	<tr>
	206	<td valign="top">BOOST_STRICT_CONFIG</td>
	207	<td>The normal behavior for compiler versions that are newer than the last known
	208	version, is to assume that they have all the same defects as the last known
	209	version. By setting this define, then compiler versions that are newer than the
	210	last known version are assumed to be fully conforming with the standard. This
	211	is probably most useful for boost developers or testers, and for those who want
	212	to use boost to test beta compiler versions.</td>
	213	</tr>
	214	<tr>
	215	<td valign="top">BOOST_ASSERT_CONFIG</td>
	216	<td>When this flag is set, if the config finds anything unknown, then it will stop
	217	with a #error rather than continue. Boost regression testers should set this
	218	define, as should anyone who wants to quickly check whether boost is supported
	219	on their platform.</td>
	220	</tr>
	221	<tr>
	222	<td valign="top" width="48%">BOOST_DISABLE_THREADS</td>
	223	<td valign="top" width="52%">When defined, disables threading support, even if the
	224	compiler in its current translation mode supports multiple threads.</td>
	225	</tr>
	226	<tr>
	227	<td valign="top">BOOST_DISABLE_WIN32</td>
	228	<td>When defined, disables the use of Win32 specific API's, even when these are
	229	available. Also has the effect of setting BOOST_DISABLE_THREADS unless
	230	BOOST_HAS_PTHREADS is set. This option may be set automatically by the config
	231	system when it detects that the compiler is in "strict mode".</td>
	232	</tr>
	233	<TR>
	234	<TD vAlign="top">BOOST_DISABLE_ABI_HEADERS</TD>
	235	<TD>Stops boost headers from including any prefix/suffix headers that normally
	236	control things like struct packing and alignment.</TD>
	237	</TR>
	238	<TR>
	239	<TD vAlign="top">BOOST_ABI_PREFIX</TD>
	240	<TD>A prefix header to include in place of whatever boost.config would normally
	241	select, any replacement should set up struct packing and alignment options as
	242	required.</TD>
	243	</TR>
	244	<TR>
	245	<TD vAlign="top">BOOST_ABI_SUFFIX</TD>
	246	<TD>A suffix header to include in place of whatever boost.config would normally
	247	select, any replacement should undo the effects of the prefix header.</TD>
	248	</TR>
	249	<TR>
	250	<TD vAlign="top">BOOST_ALL_DYN_LINK</TD>
	251	<TD>
	252	<P>Forces all libraries that have separate source, to be linked as dll's rather
	253	than static libraries on Microsoft Windows (this macro is used to turn on
	254	__declspec(dllimport) modifiers, so that the compiler knows which symbols to
	255	look for in a dll rather than in a static library).
	256	</P>
	257	<P>Note that there may be some libraries that can only be statically linked
	258	(Boost.Test for example) and others which may only be dynamically linked
	259	(Boost.Threads for example), in these cases this macro has no effect.</P>
	260	</TD>
	261	</TR>
	262	<TR>
	263	<TD vAlign="top">BOOST_WHATEVER_DYN_LINK</TD>
	264	<TD>
	265	<P>Forces library "whatever" to be linked as a dll rather than a static library on
	266	Microsoft Windows: replace the WHATEVER part of the macro name with the name of
	267	the library that you want to dynamically link to, for example use
	268	BOOST_DATE_TIME_DYN_LINK or BOOST_REGEX_DYN_LINK etc (this macro is used
	269	to turn on __declspec(dllimport) modifiers, so that the compiler knows which
	270	symbols to look for in a dll rather than in a static library).
	271	</P>
	272	<P>Note that there may be some libraries that can only be statically linked
	273	(Boost.Test for example) and others which may only be dynamically linked
	274	(Boost.Threads for example), in these cases this macro is unsupported.</P>
	275	</TD>
	276	</TR>
	277	<TR>
	278	<TD vAlign="top">BOOST_ALL_NO_LIB</TD>
	279	<TD>
	280	<P>Tells the config system not to automatically select which libraries to link
	281	against.
	282	</P>
	283	<P>Normally if a compiler supports #pragma lib, then the correct library build
	284	variant will be automatically selected and linked against, simply by the act of
	285	including one of that library's headers.  This macro turns that feature
	286	off.</P>
	287	</TD>
	288	</TR>
	289	<TR>
	290	<TD vAlign="top">BOOST_WHATEVER_NO_LIB</TD>
	291	<TD>
	292	<P>Tells the config system not to automatically select which library to link
	293	against for library "whatever", replace WHATEVER in the macro name with the
	294	name of the library; for example BOOST_DATE_TIME_NO_LIB or
	295	BOOST_REGEX_NO_LIB.
	296	</P>
	297	<P>Normally if a compiler supports #pragma lib, then the correct library build
	298	variant will be automatically selected and linked against, simply by the act of
	299	including one of that library's headers.  This macro turns that feature
	300	off.</P>
	301	</TD>
	302	</TR>
	303	<TR>
	304	<TD vAlign="top">BOOST_LIB_DIAGNOSTIC</TD>
	305	<TD>Causes the auto-linking code to output diagnostic messages indicating the name
	306	of the library that is selected for linking.</TD>
	307	</TR>
	308	<TR>
	309	<TD vAlign="top">BOOST_LIB_TOOLSET</TD>
	310	<TD>Overrides the name of the toolset part of the name of library being linked to;
	311	note if defined this must be defined to a quoted string literal, for example
	312	"abc".</TD>
	313	</TR>
	314	</table>
	315	<h4><a name="advanced_config"></a>Advanced configuration usage</h4>
	316	<p>By setting various macros on the compiler command line or by editing <<a href="../../boost/config/user.hpp">boost/config/user.hpp</a>>,
	317	the boost configuration setup can be optimised in a variety of ways.
	318	</p>
	319	<p>Boost's configuration is structured so that the user-configuration is included
	320	first (defaulting to <<a href="../../boost/config/user.hpp">boost/config/user.hpp</a>>
	321	if BOOST_USER_CONFIG is not defined). This sets up any user-defined policies,
	322	and gives the user-configuration a chance to influence what happens next.
	323	</p>
	324	<p>Next the compiler, standard library, and platform configuration files are
	325	included. These are included via macros (BOOST_COMPILER_CONFIG etc, <a href="#user_settable">
	326	see user settable macros</a>), and if the corresponding macro is undefined
	327	then a separate header that detects which compiler/standard library/platform is
	328	in use is included in order to set these. The config can be told to ignore
	329	these headers altogether if the corresponding BOOST_NO_XXX macro is set (for
	330	example BOOST_NO_COMPILER_CONFIG to disable including any compiler
	331	configuration file - <a href="#user_settable">see user settable macros</a>).
	332	</p>
	333	<p>Finally the boost configuration header, includes <<a href="../../boost/config/suffix.hpp">boost/config/suffix.hpp</a>>;
	334	this header contains any boiler plate configuration code - for example where
	335	one boost macro being set implies that another must be set also.</p>
	336	<p>The following usage examples represent just a few of the possibilities:</p>
	337	<p><u>Example 1, creating our own frozen configuration.</u></p>
	338	<p>Lets suppose that we're building boost with Visual C++ 6, and STLport 4.0. Lets
	339	suppose also that we don't intend to update our compiler or standard library
	340	any time soon. In order to avoid breaking dependencies when we update boost, we
	341	may want to "freeze" our configuration headers, so that we only have to rebuild
	342	our project if the boost code itself has changed, and not because the boost
	343	config has been updated for more recent versions of Visual C++ or STLport.
	344	We'll start by realising that the configuration files in use are: <<a href="../../boost/config/compiler/visualc.hpp">boost/config/compiler/visualc.hpp</a>>
	345	for the compiler, <<a href="../../boost/config/stdlib/stlport.hpp">boost/config/stdlib/stlport.hpp</a>>
	346	for the standard library, and <<a href="../../boost/config/platform/win32.hpp">boost/config/platform/win32.hpp</a>>
	347	for the platform. Next we'll create our own private configuration directory:
	348	boost/config/mysetup/, and copy the configuration files into there. Finally,
	349	open up <<a href="../../boost/config/user.hpp">boost/config/user.hpp</a>>
	350	and edit the following defines:</p>
	351	<pre>#define BOOST_COMPILER_CONFIG "boost/config/mysetup/visualc.hpp"
	352	#define BOOST_STDLIB_CONFIG "boost/config/mysetup/stlport.hpp"
	353	#define BOOST_USER_CONFIG "boost/config/mysetup/win32.hpp"</pre>
	354	<p>Now when you use boost, its configuration header will go straight to our
	355	"frozen" versions, and ignore the default versions, you will now be insulated
	356	from any configuration changes when you update boost. This technique is also
	357	useful if you want to modify some of the boost configuration files; for example
	358	if you are working with a beta compiler release not yet supported by boost.</p>
	359	<p><u>Example 2: skipping files that you don't need.</u></p>
	360	<p>Lets suppose that you're using boost with a compiler that is fully conformant
	361	with the standard; you're not interested in the fact that older versions of
	362	your compiler may have had bugs, because you know that your current version
	363	does not need any configuration macros setting. In a case like this, you can
	364	define BOOST_NO_COMPILER_CONFIG either on the command line, or in
	365	<boost/config/user.hpp>, and miss out the compiler configuration header
	366	altogether (actually you miss out two headers, one which works out what the
	367	compiler is, and one that configures boost for it). This has two consequences:
	368	the first is that less code has to be compiled, and the second that you have
	369	removed a dependency on two boost headers.</p>
	370	<p><u>Example 3: using configure script to freeze the boost configuration.</u></p>
	371	<p>If you are working on a unix-like platform then you can use the configure
	372	script to generate a "frozen" configuration based on your current compiler
	373	setup - <a href="#config_script">see using the configure script</a> for more
	374	details.</p>
	375	<h4><a name="testing"></a>Testing the boost configuration</h4>
	376	<p>The boost configuration library provides a full set of regression test programs
	377	under the <boost-root>/libs/config/test/ sub-directory:</p>
	378	<table border="1" cellpadding="7" cellspacing="1" width="100%">
	379	<tr>
	380	<td valign="top" width="50%"><p align="center"><b>File</b></p>
	381	</td>
	382	<td valign="top" width="50%"><p align="center"><b>Description</b></p>
	383	</td>
	384	</tr>
	385	<tr>
	386	<td valign="top" width="50%">config_info.cpp</td>
	387	<td valign="top" width="50%">Prints out a detailed description of your
	388	compiler/standard library/platform setup, plus your current boost
	389	configuration. The information provided by this program useful in setting up
	390	the boost configuration files. If you report that boost is incorrectly
	391	configured for your compiler/library/platform then please include the output
	392	from this program when reporting the changes required.</td>
	393	</tr>
	394	<tr>
	395	<td valign="top" width="50%">config_test.cpp</td>
	396	<td valign="top" width="50%">A monolithic test program that includes most of the
	397	individual test cases. This provides a quick check to see if boost is correctly
	398	configured for your compiler/library/platform.</td>
	399	</tr>
	400	<tr>
	401	<td valign="top" width="50%">limits_test.cpp</td>
	402	<td valign="top" width="50%">Tests your standard library's std::numeric_limits
	403	implementation (or its boost provided replacement if BOOST_NO_LIMITS is
	404	defined). This test file fails with most versions of numeric_limits, mainly due
	405	to the way that some compilers treat NAN's and infinity.</td>
	406	</tr>
	407	<tr>
	408	<td valign="top" width="50%">no_*pass.cpp</td>
	409	<td valign="top" width="50%">Individual compiler defect test files. Each of these
	410	should compile, if one does not then the corresponding BOOST_NO_XXX macro needs
	411	to be defined - see each test file for specific details.</td>
	412	</tr>
	413	<tr>
	414	<td valign="top" width="50%">no_*fail.cpp</td>
	415	<td valign="top" width="50%">Individual compiler defect test files. Each of these
	416	should <i>not</i> compile, if one does then the corresponding BOOST_NO_XXX
	417	macro is defined when it need not be - see each test file for specific details.</td>
	418	</tr>
	419	<tr>
	420	<td valign="top" width="50%">has_*pass.cpp</td>
	421	<td valign="top" width="50%">Individual feature test files. If one of these does <i>not</i>
	422	compile then the corresponding BOOST_HAS_XXX macro is defined when it should
	423	not be - see each test file for specific details.</td>
	424	</tr>
	425	<tr>
	426	<td valign="top" width="50%">has_*fail.cpp</td>
	427	<td valign="top" width="50%">Individual feature test files. If one of these does
	428	compile then the corresponding BOOST_HAS_XXX macro can be safely defined - see
	429	each test file for specific details.</td>
	430	</tr>
	431	</table>
	432	<p>Although you can run the configuration regression tests as individual test
	433	files, there are rather a lot of them, so there are a couple of shortcuts to
	434	help you out:</p>
	435	<p>If you have built the <a href="../../more/regression.html">boost regression test
	436	driver</a>, then you can use this to produce a nice html formatted report of
	437	the results using the supplied test file.</p>
	438	<p>Alternatively you can run the configure script like this:</p>
	439	<pre>./configure --enable-test</pre>
	440	<p>in which case the script will test the current configuration rather than
	441	creating a new one from scratch.</p>
	442	<p>If you are reporting the results of these tests for a new
	443	platform/library/compiler then please include a log of the full compiler
	444	output, the output from config_info.cpp, and the pass/fail test results.</p>
	445	<h2><a name="macro_ref"></a>Boost Macro Reference</h2>
	446	<h4><a name="defects"></a>Macros that describe defects:</h4>
	447	<p>The following macros all describe features that are required by the C++
	448	standard, if one of the following macros is defined, then it represents a
	449	defect in the compiler's conformance with the standard.</p>
	450	<table border="1" cellpadding="7" cellspacing="1" width="100%">
	451	<tr>
	452	<td valign="top" width="51%"><p align="center"><b>Macro</b></p>
	453	</td>
	454	<td valign="top" width="16%"><p align="center"><b>Section</b></p>
	455	</td>
	456	<td valign="top" width="33%"><p align="center"><b>Description</b></p>
	457	</td>
	458	</tr>
	459	<tr>
	460	<td>BOOST_BCB_PARTIAL_SPECIALIZATION_BUG</td>
	461	<td>Compiler</td>
	462	<td>The compiler exibits certain partial specialisation bug - probably Borland C++
	463	Builder specific.</td>
	464	</tr>
	465	<TR>
	466	<TD vAlign="top" width="51%">BOOST_FUNCTION_SCOPE_USING_DECLARATION_BREAKS_ADL</TD>
	467	<TD vAlign="top" width="16%">Compiler</TD>
	468	<TD vAlign="top" width="33%">Argument dependent lookup fails if there is a using
	469	declaration for the symbol being looked up in the current scope.  For
	470	example, <code>using boost::get_pointer;</code> prevents ADL from finding
	471	overloads of <code>get_pointer</code> in namespaces nested inside boost (but
	472	not elsewhere).  Probably Borland specific.</TD>
	473	</TR>
	474	<tr>
	475	<td valign="top" width="51%">BOOST_NO_ARGUMENT_DEPENDENT_LOOKUP</td>
	476	<td valign="top" width="16%">Compiler</td>
	477	<td valign="top" width="33%">Compiler does not implement argument-dependent lookup
	478	(also named Koenig lookup); see std::3.4.2 [basic.koenig.lookup]</td>
	479	</tr>
	480	<tr>
	481	<td valign="top" width="51%">BOOST_NO_AUTO_PTR</td>
	482	<td valign="top" width="16%">Standard library</td>
	483	<td valign="top" width="33%">If the compiler / library supplies non-standard or
	484	broken std::auto_ptr.</td>
	485	</tr>
	486	<tr>
	487	<td valign="top" width="51%">BOOST_NO_CTYPE_FUNCTIONS</td>
	488	<td valign="top" width="16%">Platform</td>
	489	<td valign="top" width="33%">The Platform does not provide functions for the
	490	character-classifying operations <ctype.h> and <cctype>, only
	491	macros.</td>
	492	</tr>
	493	<tr>
	494	<td valign="top" width="51%">BOOST_NO_CV_SPECIALIZATIONS</td>
	495	<td valign="top" width="16%">Compiler</td>
	496	<td valign="top" width="33%">If template specialisations for cv-qualified types
	497	conflict with a specialisation for a cv-unqualififed type.</td>
	498	</tr>
	499	<tr>
	500	<td valign="top" width="51%">BOOST_NO_CV_VOID_SPECIALIZATIONS</td>
	501	<td valign="top" width="16%">Compiler</td>
	502	<td valign="top" width="33%">If template specialisations for cv-void types
	503	conflict with a specialisation for void.</td>
	504	</tr>
	505	<tr>
	506	<td valign="top" width="51%">BOOST_NO_CWCHAR</td>
	507	<td valign="top" width="16%">Platform</td>
	508	<td valign="top" width="33%">The Platform does not provide <wchar.h> and
	509	<cwchar>.</td>
	510	</tr>
	511	<tr>
	512	<td valign="top" width="51%">BOOST_NO_CWCTYPE</td>
	513	<td valign="top" width="16%">Platform</td>
	514	<td valign="top" width="33%">The Platform does not provide <wctype.h> and
	515	<cwctype>.</td>
	516	</tr>
	517	<tr>
	518	<td valign="top" width="51%">BOOST_NO_DEPENDENT_NESTED_DERIVATIONS</td>
	519	<td valign="top" width="16%">Compiler</td>
	520	<td valign="top" width="33%">The compiler fails to compile a nested class that has
	521	a dependent base class:<pre>template<typename T>
	522	struct foo : {
	523	template<typename U>
	524	struct bar : public U {};
	525	};</pre>
	526	</td>
	527	</tr>
	528	<tr>
	529	<td valign="top" width="51%">BOOST_NO_DEPENDENT_TYPES_IN_TEMPLATE_VALUE_PARAMETERS</td>
	530	<td valign="top" width="16%">Compiler</td>
	531	<td valign="top" width="33%">Template value parameters cannot have a dependent
	532	type, for example:<pre>template<class T, typename T::type value>
	533	class X { ... };</pre>
	534	</td>
	535	</tr>
	536	<tr>
	537	<td valign="top">BOOST_NO_EXCEPTION_STD_NAMESPACE</td>
	538	<td valign="top">Standard Library</td>
	539	<td>The standard library does not put some or all of the contents of
	540	<exception> in namespace std.</td>
	541	</tr>
	542	<tr>
	543	<td valign="top">BOOST_NO_EXCEPTIONS</td>
	544	<td valign="top">Compiler</td>
	545	<td>The compiler does not support exception handling (this setting is typically
	546	required by many C++ compilers for embedded platforms). Note that there is no
	547	requirement for boost libraries to honor this configuration setting - indeed
	548	doing so may be impossible in some cases. Those libraries that do honor this
	549	will typically abort if a critical error occurs - you have been warned!</td>
	550	</tr>
	551	<tr>
	552	<td valign="top" width="51%">BOOST_NO_EXPLICIT_FUNCTION_TEMPLATE_ARGUMENTS</td>
	553	<td valign="top" width="16%">Compiler</td>
	554	<td valign="top" width="33%">Can only use deduced template arguments when calling
	555	function template instantiations.</td>
	556	</tr>
	557	<tr>
	558	<td valign="top" width="51%">BOOST_NO_FUNCTION_TEMPLATE_ORDERING</td>
	559	<td valign="top" width="16%">Compiler</td>
	560	<td valign="top" width="33%">The compiler does not perform function template
	561	ordering or its function template ordering is incorrect.
	562	<pre>template<typename T> void f(T); // #1
	563	template<typename T, typename U> void f(T (*)(U)); // #2
	564
	565	void bar(int);
	566
	567	f(&bar); // should choose #2.</pre>
	568	</td>
	569	</tr>
	570	<tr>
	571	<td valign="top" width="51%">BOOST_NO_INCLASS_MEMBER_INITIALIZATION</td>
	572	<td valign="top" width="16%">Compiler</td>
	573	<td valign="top" width="33%">Compiler violates std::9.4.2/4.</td>
	574	</tr>
	575	<tr>
	576	<td valign="top" width="51%">BOOST_NO_INTRINSIC_WCHAR_T</td>
	577	<td valign="top" width="16%">Compiler</td>
	578	<td valign="top" width="33%">The C++ implementation does not provide wchar_t, or
	579	it is really a synonym for another integral type. Use this symbol to decide
	580	whether it is appropriate to explicitly specialize a template on wchar_t if
	581	there is already a specialization for other integer types.</td>
	582	</tr>
	583	<TR>
	584	<TD vAlign="top" width="51%">BOOST_NO_IS_ABSTRACT</TD>
	585	<TD vAlign="top" width="16%">Compiler</TD>
	586	<TD vAlign="top" width="33%">The C++ compiler does not support SFINAE with
	587	abstract types, this is covered by <A href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#337">
	588	Core Language DR337</A>, but is not part of the current standard.
	589	Fortunately most compilers that support SFINAE also support this DR.</TD>
	590	</TR>
	591	<tr>
	592	<td valign="top" width="51%">BOOST_NO_LIMITS</td>
	593	<td valign="top" width="16%">Standard library</td>
	594	<td valign="top" width="33%">The C++ implementation does not provide the
	595	<limits> header. Never check for this symbol in library code; always
	596	include <boost/limits.hpp>, which guarantees to provide <code>std::numeric_limits</code>.</td>
	597	</tr>
	598	<tr>
	599	<td valign="top" width="51%">BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS</td>
	600	<td valign="top" width="16%">Standard library</td>
	601	<td valign="top" width="33%">Constants such as numeric_limits<T>::is_signed
	602	are not available for use at compile-time.</td>
	603	</tr>
	604	<tr>
	605	<td>BOOST_NO_LONG_LONG_NUMERIC_LIMITS</td>
	606	<td>Standard library</td>
	607	<td>There is no specialization for numeric_limits<long long> and
	608	numeric_limits<unsigned long long>. <boost/limits.hpp> will then
	609	add these specializations as a standard library "fix" only if the compiler
	610	supports the long long datatype.</td>
	611	</tr>
	612	<tr>
	613	<td>BOOST_NO_MEMBER_FUNCTION_SPECIALIZATIONS</td>
	614	<td>Compiler</td>
	615	<td>The compiler does not support the specialization of individual member
	616	functions of template classes.</td>
	617	</tr>
	618	<tr>
	619	<td valign="top" width="51%">BOOST_NO_MEMBER_TEMPLATE_KEYWORD</td>
	620	<td valign="top" width="16%">Compiler</td>
	621	<td valign="top" width="33%">If the compiler supports member templates, but not
	622	the template keyword when accessing member template classes.</td>
	623	</tr>
	624	<tr>
	625	<td valign="top" width="51%">BOOST_NO_MEMBER_TEMPLATE_FRIENDS</td>
	626	<td valign="top" width="16%">Compiler</td>
	627	<td valign="top" width="33%">Member template friend syntax ("template<class
	628	P> friend class frd;") described in the C++ Standard, 14.5.3, not supported.</td>
	629	</tr>
	630	<tr>
	631	<td valign="top" width="51%">BOOST_NO_MEMBER_TEMPLATES</td>
	632	<td valign="top" width="16%">Compiler</td>
	633	<td valign="top" width="33%">Member template functions not fully supported.</td>
	634	</tr>
	635	<tr>
	636	<td>BOOST_NO_MS_INT64_NUMERIC_LIMITS</td>
	637	<td>Standard library</td>
	638	<td>There is no specialization for numeric_limits<__int64> and
	639	numeric_limits<unsigned __int64>. <boost/limits.hpp> will then add
	640	these specializations as a standard library "fix", only if the compiler
	641	supports the __int64 datatype.</td>
	642	</tr>
	643	<tr>
	644	<td valign="top" width="51%">BOOST_NO_OPERATORS_IN_NAMESPACE</td>
	645	<td valign="top" width="16%">Compiler</td>
	646	<td valign="top" width="33%">Compiler requires inherited operator friend functions
	647	to be defined at namespace scope, then using'ed to boost. Probably GCC
	648	specific. See <a href="../../boost/operators.hpp">boost/operators.hpp</a> for
	649	example.</td>
	650	</tr>
	651	<tr>
	652	<td valign="top" width="51%">BOOST_NO_POINTER_TO_MEMBER_CONST</td>
	653	<td valign="top" width="16%">Compiler</td>
	654	<td valign="top" width="33%">The compiler does not correctly handle pointers to
	655	const member functions, preventing use of these in overloaded function
	656	templates. See <a href="../../boost/functional.hpp">boost/functional.hpp</a> for
	657	example.</td>
	658	</tr>
	659	<TR>
	660	<TD vAlign="top" width="51%">BOOST_NO_POINTER_TO_MEMBER_TEMPLATE_PARAMETERS</TD>
	661	<TD vAlign="top" width="16%">Compiler</TD>
	662	<TD vAlign="top" width="33%">Pointers to members don't work when used as template
	663	parameters.</TD>
	664	</TR>
	665	<tr>
	666	<td valign="top" width="51%">BOOST_NO_PRIVATE_IN_AGGREGATE</td>
	667	<td valign="top" width="16%">Compiler</td>
	668	<td valign="top" width="33%">The compiler misreads 8.5.1, treating classes as
	669	non-aggregate if they contain private or protected member functions.</td>
	670	</tr>
	671	<TR>
	672	<TD vAlign="top" width="51%">BOOST_NO_SFINAE</TD>
	673	<TD vAlign="top" width="16%">Compiler</TD>
	674	<TD vAlign="top" width="33%">The compiler does not support the "Substitution
	675	Failure Is Not An Error" meta-programming idiom.</TD>
	676	</TR>
	677	<tr>
	678	<td valign="top" width="51%">BOOST_NO_STD_ALLOCATOR</td>
	679	<td valign="top" width="16%">Standard library</td>
	680	<td valign="top" width="33%">The C++ standard library does not provide a standards
	681	conforming std::allocator.</td>
	682	</tr>
	683	<tr>
	684	<td valign="top" width="51%">BOOST_NO_STD_DISTANCE</td>
	685	<td valign="top" width="16%">Standard library</td>
	686	<td valign="top" width="33%">The platform does not have a conforming version of
	687	std::distance.</td>
	688	</tr>
	689	<tr>
	690	<td valign="top" width="51%">BOOST_NO_STD_ITERATOR</td>
	691	<td valign="top" width="16%">Standard library</td>
	692	<td valign="top" width="33%">The C++ implementation fails to provide the
	693	std::iterator class.</td>
	694	</tr>
	695	<tr>
	696	<td valign="top" width="51%">BOOST_NO_STD_ITERATOR_TRAITS</td>
	697	<td valign="top" width="16%">Standard library</td>
	698	<td valign="top" width="33%">The compiler does not provide a standard compliant
	699	implementation of std::iterator_traits. Note that the compiler may still have a
	700	non-standard implementation.</td>
	701	</tr>
	702	<tr>
	703	<td valign="top" width="51%">BOOST_NO_STD_LOCALE</td>
	704	<td valign="top" width="16%">Standard library</td>
	705	<td valign="top" width="33%">The standard library lacks std::locale.</td>
	706	</tr>
	707	<tr>
	708	<td valign="top" width="51%">BOOST_NO_STD_MESSAGES</td>
	709	<td valign="top" width="16%">Standard library</td>
	710	<td valign="top" width="33%">The standard library lacks a conforming std::messages
	711	facet.</td>
	712	</tr>
	713	<tr>
	714	<td valign="top" width="51%">BOOST_NO_STD_MIN_MAX</td>
	715	<td valign="top" width="16%">Standard library</td>
	716	<td valign="top" width="33%">The C++ standard library does not provide the min()
	717	and max() template functions that should be in <algorithm>.</td>
	718	</tr>
	719	<tr>
	720	<td valign="top">BOOST_NO_STD_OUTPUT_ITERATOR_ASSIGN</td>
	721	<td valign="top">Standard library</td>
	722	<td valign="top">Defined if the standard library's output iterators are not
	723	assignable.</td>
	724	</tr>
	725	<tr>
	726	<td valign="top" width="51%">BOOST_NO_STD_USE_FACET</td>
	727	<td valign="top" width="16%">Standard library</td>
	728	<td valign="top" width="33%">The standard library lacks a conforming
	729	std::use_facet.</td>
	730	</tr>
	731	<tr>
	732	<td>BOOST_NO_STD_WSTREAMBUF</td>
	733	<td>Standard library</td>
	734	<td>The standard library's implementation of std::basic_streambuf<wchar_t>
	735	is either missing, incomplete, or buggy.</td>
	736	</tr>
	737	<tr>
	738	<td valign="top" width="51%">BOOST_NO_STD_WSTRING</td>
	739	<td valign="top" width="16%">Standard library</td>
	740	<td valign="top" width="33%">The standard library lacks std::wstring.</td>
	741	</tr>
	742	<tr>
	743	<td valign="top" width="51%">BOOST_NO_STDC_NAMESPACE</td>
	744	<td valign="top" width="16%">Compiler/Platform</td>
	745	<td valign="top" width="33%">The contents of C++ standard headers for C library
	746	functions (the <c...> headers) have not been placed in namespace std.
	747	This test is difficult - some libraries "fake" the std C functions by adding
	748	using declarations to import them into namespace std, unfortunately they don't
	749	necessarily catch all of them...</td>
	750	</tr>
	751	<tr>
	752	<td valign="top" width="51%">BOOST_NO_STRINGSTREAM</td>
	753	<td valign="top" width="16%">Standard library</td>
	754	<td valign="top" width="33%">The C++ implementation does not provide the
	755	<sstream> header.</td>
	756	</tr>
	757	<tr>
	758	<td valign="top" width="51%">BOOST_NO_SWPRINTF</td>
	759	<td valign="top" width="16%">Platform</td>
	760	<td valign="top" width="33%">The platform does not have a conforming version of
	761	swprintf.</td>
	762	</tr>
	763	<tr>
	764	<td valign="top" width="51%">BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION</td>
	765	<td valign="top" width="16%">Compiler</td>
	766	<td valign="top" width="33%">Class template partial specialization (14.5.4
	767	[temp.class.spec]) not supported.</td>
	768	</tr>
	769	<tr>
	770	<td valign="top" width="51%">BOOST_NO_TEMPLATED_ITERATOR_CONSTRUCTORS</td>
	771	<td valign="top" width="16%">Standard library</td>
	772	<td valign="top" width="33%">The standard library does not provide templated
	773	iterator constructors for its containers.</td>
	774	</tr>
	775	<tr>
	776	<td>BOOST_NO_TEMPLATE_TEMPLATES</td>
	777	<td>Compiler</td>
	778	<td>The compiler does not support template template parameters.</td>
	779	</tr>
	780	<tr>
	781	<td>BOOST_NO_UNREACHABLE_RETURN_DETECTION</td>
	782	<td>Compiler</td>
	783	<td>If a return is unreachable, then no return statement should be required,
	784	however some compilers insist on it, while other issue a bunch of warnings if
	785	it is in fact present.</td>
	786	</tr>
	787	<TR>
	788	<TD vAlign="top" width="51%">BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE</TD>
	789	<TD vAlign="top" width="16%">Compiler</TD>
	790	<TD vAlign="top" width="33%">The compiler will not accept a using
	791	declaration that brings a function from a typename used as a base
	792	class into a derived class if functions of the same name are present
	793	in the derived class.</TD>
	794	</TR>
	795	<tr>
	796	<td valign="top" width="51%">BOOST_NO_USING_TEMPLATE</td>
	797	<td valign="top" width="16%">Compiler</td>
	798	<td valign="top" width="33%">The compiler will not accept a using declaration that
	799	imports a template class or function from another namespace. Originally a
	800	Borland specific problem with imports to/from the global namespace, extended to
	801	MSVC6 which has a specific issue with importing template classes (but not
	802	functions).</td>
	803	</tr>
	804	<tr>
	805	<td valign="top" width="51%">BOOST_NO_VOID_RETURNS</td>
	806	<td valign="top" width="16%">Compiler</td>
	807	<td valign="top" width="33%">The compiler does not allow a void function to return
	808	the result of calling another void function.
	809	<pre>void f() {}
	810	void g() { return f(); }</pre>
	811	</td>
	812	</tr>
	813	</table>
	814	<h4><a name="features"></a>Macros that describe optional features:</h4>
	815	<p>The following macros describe features that are not required by the C++
	816	standard. The macro is only defined if the feature is present.</p>
	817	<table border="1" cellpadding="7" cellspacing="1" width="100%">
	818	<tr>
	819	<td valign="top" width="48%"><p align="center"><b>Macro</b></p>
	820	</td>
	821	<td valign="top" width="15%"><p align="center"><b>Section</b></p>
	822	</td>
	823	<td valign="top" width="37%"><p align="center"><b>Description</b></p>
	824	</td>
	825	</tr>
	826	<tr>
	827	<td valign="top" width="48%">BOOST_HAS_BETHREADS</td>
	828	<td valign="top" width="15%">Platform</td>
	829	<td valign="top" width="37%">The platform supports BeOS style threads.</td>
	830	</tr>
	831	<tr>
	832	<td>BOOST_HAS_CLOCK_GETTIME</td>
	833	<td>Platform</td>
	834	<td>The platform has the POSIX API clock_gettime.</td>
	835	</tr>
	836	<TR>
	837	<TD>BOOST_HAS_DECLSPEC
	838	</TD>
	839	<TD>Compiler</TD>
	840	<TD>The compiler uses __declspec(dllexport) and __declspec(dllimport) to
	841	export/import symbols from dll's.</TD>
	842	</TR>
	843	<tr>
	844	<td>BOOST_HAS_DIRENT_H</td>
	845	<td>Platform</td>
	846	<td>The platform has the POSIX header <dirent.h>.</td>
	847	</tr>
	848	<tr>
	849	<td>BOOST_HAS_FTIME</td>
	850	<td>Platform</td>
	851	<td>The platform has the Win32 API GetSystemTimeAsFileTime.</td>
	852	</tr>
	853	<tr>
	854	<td>BOOST_HAS_GETTIMEOFDAY</td>
	855	<td>Platform</td>
	856	<td>The platform has the POSIX API gettimeofday.</td>
	857	</tr>
	858	<tr>
	859	<td valign="top" width="48%">BOOST_HAS_HASH</td>
	860	<td valign="top" width="15%">Standard library</td>
	861	<td valign="top" width="37%">The C++ implementation provides the (SGI) hash_set or
	862	hash_map classes.</td>
	863	</tr>
	864	<tr>
	865	<td>BOOST_HAS_LONG_LONG</td>
	866	<td>Compiler</td>
	867	<td>The compiler supports the long long data type.</td>
	868	</tr>
	869	<tr>
	870	<td valign="top" width="48%">BOOST_HAS_MACRO_USE_FACET</td>
	871	<td valign="top" width="15%">Standard library</td>
	872	<td valign="top" width="37%">The standard library lacks a conforming
	873	std::use_facet, but has a macro _USE(loc, Type) that does the job. This is
	874	primarily for the Dinkumware std lib.</td>
	875	</tr>
	876	<tr>
	877	<td>BOOST_HAS_MS_INT64</td>
	878	<td>Compiler</td>
	879	<td>The compiler supports the __int64 data type.</td>
	880	</tr>
	881	<tr>
	882	<td>BOOST_HAS_NANOSLEEP</td>
	883	<td>Platform</td>
	884	<td>The platform has the POSIX API nanosleep.</td>
	885	</tr>
	886	<tr>
	887	<td valign="top" width="48%">BOOST_HAS_NL_TYPES_H</td>
	888	<td valign="top" width="15%">Platform</td>
	889	<td valign="top" width="37%">The platform has an <nl_types.h>.</td>
	890	</tr>
	891	<tr>
	892	<td>BOOST_HAS_NRVO</td>
	893	<td>Compiler</td>
	894	<td>Indicated that the compiler supports the named return value optimization
	895	(NRVO). Used to select the most efficient implementation for some function. See <a href="../../boost/operators.hpp">
	896	boost/operators.hpp</a> for example.</td>
	897	</tr>
	898	<tr>
	899	<td valign="top">BOOST_HAS_PARTIAL_STD_ALLOCATOR</td>
	900	<td>Standard Library</td>
	901	<td>The standard library has a partially conforming std::allocator class, but
	902	without any of the member templates.</td>
	903	</tr>
	904	<tr>
	905	<td>BOOST_HAS_PTHREAD_DELAY_NP</td>
	906	<td>Platform</td>
	907	<td>The platform has the POSIX API pthread_delay_np.</td>
	908	</tr>
	909	<tr>
	910	<td>BOOST_HAS_PTHREAD_MUTEXATTR_SETTYPE</td>
	911	<td>Platform</td>
	912	<td>The platform has the POSIX API pthread_mutexattr_settype.</td>
	913	</tr>
	914	<tr>
	915	<td>BOOST_HAS_PTHREAD_YIELD</td>
	916	<td>Platform</td>
	917	<td>The platform has the POSIX API pthread_yield.</td>
	918	</tr>
	919	<tr>
	920	<td valign="top" width="48%">BOOST_HAS_PTHREADS</td>
	921	<td valign="top" width="15%">Platform</td>
	922	<td valign="top" width="37%">The platform support POSIX style threads.</td>
	923	</tr>
	924	<tr>
	925	<td>BOOST_HAS_SCHED_YIELD</td>
	926	<td>Platform</td>
	927	<td>The platform has the POSIX API sched_yield.</td>
	928	</tr>
	929	<tr>
	930	<td>BOOST_HAS_SGI_TYPE_TRAITS</td>
	931	<td>Compiler/standard library</td>
	932	<td>The compiler has native support for SGI style type traits.</td>
	933	</tr>
	934	<tr>
	935	<td>BOOST_HAS_STDINT_H</td>
	936	<td>Platform</td>
	937	<td>The platform has a <stdint.h></td>
	938	</tr>
	939	<tr>
	940	<td valign="top" width="48%">BOOST_HAS_SLIST</td>
	941	<td valign="top" width="15%">Standard library</td>
	942	<td valign="top" width="37%">The C++ implementation provides the (SGI) slist
	943	class.</td>
	944	</tr>
	945	<tr>
	946	<td valign="top" width="48%">BOOST_HAS_STLP_USE_FACET</td>
	947	<td valign="top" width="15%">Standard library</td>
	948	<td valign="top" width="37%">The standard library lacks a conforming
	949	std::use_facet, but has a workaround class-version that does the job. This is
	950	primarily for the STLport std lib.</td>
	951	</tr>
	952	<tr>
	953	<td valign="top" width="48%">BOOST_HAS_THREADS</td>
	954	<td valign="top" width="15%">Platform/compiler</td>
	955	<td valign="top" width="37%">Defined if the compiler, in its current translation
	956	mode, supports multiple threads of execution.</td>
	957	</tr>
	958	<tr>
	959	<td valign="top" width="48%">BOOST_HAS_TWO_ARG_USE_FACET</td>
	960	<td valign="top" width="15%">Standard library</td>
	961	<td valign="top" width="37%">The standard library lacks a conforming
	962	std::use_facet, but has a two argument version that does the job. This is
	963	primarily for the Rogue Wave std lib.</td>
	964	</tr>
	965	<tr>
	966	<td valign="top" width="48%">BOOST_HAS_UNISTD_H</td>
	967	<td valign="top" width="15%">Platform</td>
	968	<td valign="top" width="37%">The Platform provides <unistd.h>.</td>
	969	</tr>
	970	<tr>
	971	<td valign="top" width="48%">BOOST_HAS_WINTHREADS</td>
	972	<td valign="top" width="15%">Platform</td>
	973	<td valign="top" width="37%">The platform supports MS Windows style threads.</td>
	974	</tr>
	975	<tr>
	976	<td valign="top" width="48%">BOOST_MSVC_STD_ITERATOR</td>
	977	<td valign="top" width="15%">Standard library</td>
	978	<td valign="top" width="37%">Microsoft's broken version of std::iterator is being
	979	used. This implies that std::iterator takes no more than two template
	980	parameters.</td>
	981	</tr>
	982	<tr>
	983	<td valign="top" width="48%">BOOST_MSVC6_MEMBER_TEMPLATES</td>
	984	<td valign="top" width="15%">Compiler</td>
	985	<td valign="top" width="37%">Microsoft Visual C++ 6.0 has enough member template
	986	idiosyncrasies (being polite) that BOOST_NO_MEMBER_TEMPLATES is defined for
	987	this compiler. BOOST_MSVC6_MEMBER_TEMPLATES is defined to allow compiler
	988	specific workarounds. This macro gets defined automatically if
	989	BOOST_NO_MEMBER_TEMPLATES is not defined - in other words this is treated as a
	990	strict subset of the features required by the standard.</td>
	991	</tr>
	992	<tr>
	993	<td valign="top" width="48%">BOOST_HAS_STDINT_H</td>
	994	<td valign="top" width="15%">Platform</td>
	995	<td valign="top" width="37%">There are no 1998 C++ Standard headers
	996	<stdint.h> or <cstdint>, although the 1999 C Standard does include
	997	<stdint.h>. If <stdint.h> is present, <boost/stdint.h> can
	998	make good use of it, so a flag is supplied (signalling presence; thus the
	999	default is not present, conforming to the current C++ standard).</td>
	1000	</tr>
	1001	</table>
	1002	<h4><a name="helpers"></a>Boost Helper Macros</h4>
	1003	<p>The following macros are either simple helpers, or macros that provide
	1004	workarounds for compiler/standard library defects.</p>
	1005	<table border="1" cellpadding="7" cellspacing="1" width="100%">
	1006	<tr>
	1007	<td valign="top" width="50%"><p align="center"><b>Macro</b></p>
	1008	</td>
	1009	<td valign="top" width="50%"><p align="center"><b>Description</b></p>
	1010	</td>
	1011	</tr>
	1012	<tr>
	1013	<td valign="top" width="50%">BOOST_DEDUCED_TYPENAME</td>
	1014	<td valign="top" width="50%">Some compilers don't support the use of <code>typename</code>
	1015	for dependent types in deduced contexts. This macro expands to nothing on those
	1016	compilers, and <code>typename</code> elsewhere. For example, replace:<pre>template <class T> void f(T, typename T::type);</pre>
	1017	<p>with:</p>
	1018	<pre>template <class T> void f(T, BOOST_DEDUCED_TYPENAME T::type);</pre>
	1019	</td>
	1020	</tr>
	1021	<tr>
	1022	<td>BOOST_STD_EXTENSION_NAMESPACE</td>
	1023	<td>The namespace used for std library extensions (hashtable classes etc).</td>
	1024	</tr>
	1025	<tr>
	1026	<td valign="top" width="50%">BOOST_STATIC_CONSTANT(Type, assignment)</td>
	1027	<td valign="top" width="50%">On compilers which don't allow in-class
	1028	initialization of static integral constant members, we must use enums as a
	1029	workaround if we want the constants to be available at compile-time. This macro
	1030	gives us a convenient way to declare such constants. For example instead of:<pre>struct foo{
	1031	static const int value = 2;
	1032	};</pre>
	1033	<p>use:</p>
	1034	<pre>struct foo{
	1035	BOOST_STATIC_CONSTANT(int, value = 2);
	1036	};</pre>
	1037	</td>
	1038	</tr>
	1039	<tr>
	1040	<td>BOOST_UNREACHABLE_RETURN(result)</td>
	1041	<td>Normally evaluates to nothing, but evaluates to <font face="Courier New">return
	1042	x;</font> if the compiler requires a return, even when it can never be
	1043	reached.</td>
	1044	</tr>
	1045	<tr>
	1046	<td>BOOST_EXPLICIT_TEMPLATE_TYPE(t)<br>
	1047	BOOST_EXPLICIT_TEMPLATE_NON_TYPE(t, v)<br>
	1048	BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE(t)<br>
	1049	BOOST_APPEND_EXPLICIT_TEMPLATE_NON_TYPE(t, v)<br>
	1050	</td>
	1051	<td>Some compilers silently "fold" different function template instantiations if
	1052	some of the template parameters don't appear in the function parameter list.
	1053	For instance:
	1054	<pre> #include <iostream>
	1055	#include <ostream>
	1056	#include <typeinfo>
	1057
	1058	template <int n>
	1059	void f() { std::cout << n << ' '; }
	1060
	1061	template <typename T>
	1062	void g() { std::cout << typeid(T).name() << ' '; }
	1063
	1064	int main() {
	1065	f<1>();
	1066	f<2>();
	1067
	1068	g<int>();
	1069	g<double>();
	1070	}
	1071	</pre>
	1072	incorrectly outputs <tt>"2 2 double double "</tt> on VC++ 6. These macros, to
	1073	be used in the function parameter list, fix the problem without effects on the
	1074	calling syntax. For instance, in the case above write:
	1075	<pre> template <int n>
	1076	void f(BOOST_EXPLICIT_TEMPLATE_NON_TYPE(int, n)) { ... }
	1077
	1078	template <typename T>
	1079	void g(BOOST_EXPLICIT_TEMPLATE_TYPE(T)) { ... }
	1080	</pre>
	1081	Beware that they can declare (for affected compilers) a dummy <i>defaulted</i> parameter,
	1082	so they
	1083	<br>
	1084	<br>
	1085	a) should be always invoked at the end of the parameter list
	1086	<br>
	1087	b) can't be used if your function template is multiply declared.
	1088	<br>
	1089	<br>
	1090	Furthermore, in order to add any needed comma separator, an "APPEND_*" version
	1091	must be used when the macro invocation appears after a normal parameter
	1092	declaration or after the invocation of another macro of this same group.
	1093	</td>
	1094	</tr>
	1095	<tr>
	1096	<td valign="top" width="50%">BOOST_USE_FACET(Type, loc)</td>
	1097	<td valign="top" width="50%">When the standard library does not have a comforming
	1098	std::use_facet there are various workarounds available, but they differ from
	1099	library to library. This macro provides a consistent way to access a locale's
	1100	facets. For example, replace:<pre>std::use_facet<Type>(loc);</pre>
	1101	<p>with:</p>
	1102	<pre>BOOST_USE_FACET(Type, loc);</pre>
	1103	<p>Note do not add a std:: prefix to the front of BOOST_USE_FACET.</p>
	1104	</td>
	1105	</tr>
	1106	<tr>
	1107	<td valign="top" width="50%">BOOST_HAS_FACET(Type, loc)</td>
	1108	<td valign="top" width="50%">When the standard library does not have a comforming
	1109	std::has_facet there are various workarounds available, but they differ from
	1110	library to library. This macro provides a consistent way to check a locale's
	1111	facets. For example, replace:<pre>std::has_facet<Type>(loc);</pre>
	1112	<p>with:</p>
	1113	<pre>BOOST_HAS_FACET(Type, loc);</pre>
	1114	<p>Note do not add a std:: prefix to the front of BOOST_HAS_FACET.</p>
	1115	</td>
	1116	</tr>
	1117	<tr>
	1118	<td valign="top" width="50%">BOOST_NESTED_TEMPLATE</td>
	1119	<td valign="top" width="50%">Member templates are supported by some compilers even
	1120	though they can't use the A::template member<U> syntax, as a workaround
	1121	replace:<pre>typedef typename A::template rebind<U> binder;</pre>
	1122	<p>with:</p>
	1123	<pre>typedef typename A::BOOST_NESTED_TEMPLATE rebind<U> binder;</pre>
	1124	</td>
	1125	</tr>
	1126	<tr>
	1127	<td valign="top" width="50%">BOOST_STRINGIZE(X)</td>
	1128	<td valign="top" width="50%">Converts the parameter X to a string after macro
	1129	replacement on X has been performed.</td>
	1130	</tr>
	1131	<tr>
	1132	<td valign="top" width="50%">BOOST_JOIN(X,Y)</td>
	1133	<td valign="top" width="50%">This piece of macro magic joins the two arguments
	1134	together, even when one of the arguments is itself a macro (see 16.3.1 in C++
	1135	standard). This is normally used to create a mangled name in combination with a
	1136	predefined macro such a __LINE__.</td>
	1137	</tr>
	1138	</table>
	1139	<h4><a name="info_macros"></a>Boost Informational Macros</h4>
	1140	<p>The following macros describe boost features; these are the generally speaking
	1141	the only boost macros that should be tested in user code.</p>
	1142	<table border="1" cellpadding="7" cellspacing="1" width="100%">
	1143	<tr>
	1144	<td valign="top" width="33%"><p align="center"><b>Macro</b></p>
	1145	</td>
	1146	<td valign="top" width="33%"><p align="center"><b>Header</b></p>
	1147	</td>
	1148	<td valign="top" width="33%"><p align="center"><b>Description</b></p>
	1149	</td>
	1150	</tr>
	1151	<tr>
	1152	<td valign="top" width="33%">BOOST_VERSION</td>
	1153	<td valign="top" width="33%"><boost/version.hpp></td>
	1154	<td valign="top" width="33%">Describes the boost version number in XXYYZZ format
	1155	such that: (BOOST_VERSION % 100) is the sub-minor version, ((BOOST_VERSION /
	1156	100) % 1000) is the minor version, and (BOOST_VERSION / 100000) is the major
	1157	version.</td>
	1158	</tr>
	1159	<tr>
	1160	<td valign="top" width="33%">BOOST_NO_INT64_T</td>
	1161	<td valign="top" width="33%"><boost/cstdint.hpp><p><boost/stdint.h></p>
	1162	</td>
	1163	<td valign="top" width="33%">Defined if there are no 64-bit integral types:
	1164	int64_t, uint64_t etc.</td>
	1165	</tr>
	1166	<tr>
	1167	<td valign="top" width="33%">BOOST_NO_INTEGRAL_INT64_T</td>
	1168	<td valign="top" width="33%"><boost/cstdint.hpp><p><boost/stdint.h></p>
	1169	</td>
	1170	<td valign="top" width="33%">Defined if int64_t as defined by
	1171	<boost/cstdint.hpp> is not usable in integral constant expressions.</td>
	1172	</tr>
	1173	<tr>
	1174	<td valign="top">BOOST_MSVC</td>
	1175	<td valign="top"><boost/config.hpp></td>
	1176	<td valign="top">Defined if the compiler is really Microsoft Visual C++, as
	1177	opposed to one of the many other compilers that also define _MSC_VER.</td>
	1178	</tr>
	1179	<tr>
	1180	<td valign="top">BOOST_INTEL</td>
	1181	<td valign="top"><boost/config.hpp></td>
	1182	<td valign="top">Defined if the compiler is an Intel compiler, takes the same
	1183	value as the compiler version macro.</td>
	1184	</tr>
	1185	<TR>
	1186	<TD vAlign="top">BOOST_WINDOWS</TD>
	1187	<TD vAlign="top"><boost/config.hpp></TD>
	1188	<TD vAlign="top">Defined if the Windows platform API is available.</TD>
	1189	</TR>
	1190	<tr>
	1191	<td>BOOST_DINKUMWARE_STDLIB</td>
	1192	<td><boost/config.hpp></td>
	1193	<td>Defined if the dinkumware standard library is in use, takes the same value as
	1194	the Dinkumware library version macro _CPPLIB_VER if defined, otherwise 1.</td>
	1195	</tr>
	1196	<tr>
	1197	<td valign="top" width="33%">BOOST_NO_WREGEX</td>
	1198	<td valign="top" width="33%"><boost/regex.hpp></td>
	1199	<td valign="top" width="33%">Defined if the regex library does not support wide
	1200	character regular expressions.</td>
	1201	</tr>
	1202	<tr>
	1203	<td valign="top" width="33%">BOOST_COMPILER</td>
	1204	<td valign="top" width="33%"><boost/config.hpp></td>
	1205	<td valign="top" width="33%">Defined as a string describing the name and version
	1206	number of the compiler in use. Mainly for debugging the configuration.</td>
	1207	</tr>
	1208	<tr>
	1209	<td valign="top" width="33%">BOOST_STDLIB</td>
	1210	<td valign="top" width="33%"><boost/config.hpp></td>
	1211	<td valign="top" width="33%">Defined as a string describing the name and version
	1212	number of the standard library in use. Mainly for debugging the configuration.</td>
	1213	</tr>
	1214	<tr>
	1215	<td valign="top" width="33%">BOOST_PLATFORM</td>
	1216	<td valign="top" width="33%"><boost/config.hpp></td>
	1217	<td valign="top" width="33%">Defined as a string describing the name of the
	1218	platform. Mainly for debugging the configuration.</td>
	1219	</tr>
	1220	</table>
	1221	<h2><a name="guidelines"></a></h2>
	1222	<H4><A name="source"></A>Macros for libraries with separate source code</H4>
	1223	<P>The following macros and helper headers are of use to authors whose libraries
	1224	include separate source code, and are intended to address two issues: fixing
	1225	the ABI of the compiled library, and selecting which compiled library to link
	1226	against based upon the compilers settings.</P>
	1227	<H5>ABI Fixing</H5>
	1228	<P>When linking against a pre-compiled library it vital that the ABI used by the
	1229	compiler when building the library <EM>matches</EM> <EM>exactly</EM> the ABI
	1230	used by the code using the library.  In this case ABI means things like
	1231	the struct packing arrangement used, the name mangling scheme used, or the size
	1232	of some types (enum types for example).  This is separate from things like
	1233	threading support, or runtime library variations, which have to be dealt with
	1234	by build variants.  To put this in perspective there is one compiler
	1235	(Borland's) that has so many compiler options that make subtle changes to the
	1236	ABI, that at least in theory there 3200 combinations, and that's without
	1237	considering runtime library variations.  Fortunately these variations can
	1238	be managed by #pragma's that tell the compiler what ABI to use for the types
	1239	declared in your library, in order to avoid sprinkling #pragma's all over the
	1240	boost headers, there are some prefix and suffix headers that do the job,
	1241	typical usage would be:</P>
	1242	<PRE>#ifndef MY_INCLUDE_GUARD
	1243	#define MY_INCLUDE_GUARD
	1244
	1245	// all includes go here:
	1246	#include <boost/config.hpp>
	1247	#include <whatever>
	1248
	1249	#ifdef BOOST_HAS_ABI_HEADERS
	1250	# include BOOST_ABI_PREFIX
	1251	#endif
	1252
	1253	namespace boost{
	1254	// your code goes here
	1255	}
	1256
	1257	#ifdef BOOST_HAS_ABI_HEADERS
	1258	# include BOOST_ABI_SUFFIX
	1259	#endif
	1260
	1261
	1262	#endif // include guard
	1263	</PRE>
	1264	<P>The user can disable this mechanism by defining BOOST_DISABLE_ABI_HEADERS, or
	1265	they can define BOOST_ABI_PREFIX and/or BOOST_ABI_SUFFIX to point to their own
	1266	prefix/suffix headers if they so wish.</P>
	1267	<H5>Automatic library selection</H5>
	1268	<P>It is essential that users link to a build of a library which was built against
	1269	the same runtime library that their application will be built against - if this
	1270	does not happen then the library will not be binary compatible with their own
	1271	code - and there is a high likelihood  that their application will
	1272	experience runtime crashes.  These kinds of problems can be extremely
	1273	time consuming and difficult to debug, and often lead to frustrated users and
	1274	authors alike (simply selecting the right library to link against is not as
	1275	easy as it seems when their are 6-8 of them to chose from, and some users seem
	1276	to be blissfully unaware that there even are different runtimes available to
	1277	them).</P>
	1278	<P>To solve this issue, some compilers allow source code to contain #pragma's that
	1279	instruct the linker which library to link against, all the user need do is
	1280	include the headers they need, place the compiled libraries in their library
	1281	search path, and the compiler and linker do the rest.  Boost.config
	1282	supports this via the header <boost/config/auto_link.hpp>, before
	1283	including this header one or more of the following macros need to be defined:</P>
	1284	<P>
	1285	<TABLE id="Table1" cellSpacing="1" cellPadding="1" width="100%" border="1">
	1286	<TR>
	1287	<TD>BOOST_LIB_NAME</TD>
	1288	<TD>
	1289	Required: An identifier containing the basename of the library, for
	1290	example 'boost_regex'.</TD>
	1291	</TR>
	1292	<TR>
	1293	<TD>BOOST_DYN_LINK</TD>
	1294	<TD>Optional: when set link to dll rather than static library.</TD>
	1295	</TR>
	1296	<TR>
	1297	<TD>BOOST_LIB_DIAGNOSTIC</TD>
	1298	<TD>Optional: when set the header will print out the name of the library selected
	1299	(useful for debugging).</TD>
	1300	</TR>
	1301	</TABLE>
	1302	</P>
	1303	<P>If the compiler supports this mechanism, then it will be told to link against
	1304	the appropriately named library, the actual algorithm used to mangle the name
	1305	of the library is documented inside <boost/config/auto_link.hpp> and has
	1306	to match that used to create the libraries via bjam 's install rules.</P>
	1307	<P>Typical usage would be:</P>
	1308	<PRE>//
	1309	// Don't include auto-linking code if the user has disabled it by
	1310	// defining BOOST_WHATEVER_NO_LIB, or if this is one of our own
	1311	// source files (signified by BOOST_WHATEVER_SOURCE):
	1312	//
	1313	#if !defined(BOOST_WHATEVER_NO_LIB) && !defined(BOOST_WHATEVER_SOURCE)
	1314	# define BOOST_LIB_NAME boost_whatever
	1315	# ifdef BOOST_WHATEVER_DYN_LINK
	1316	# define BOOST_DYN_LINK
	1317	# endif
	1318	# include <boost/config/auto_link.hpp>
	1319	#endif
	1320	</PRE>
	1321	<H2>Guidelines for Boost Authors</H2>
	1322	<p>The <a href="../../boost/config.hpp">boost/config.hpp</a> header is used to
	1323	pass configuration information to other boost files, allowing them to cope with
	1324	platform dependencies such as arithmetic byte ordering, compiler pragmas, or
	1325	compiler shortcomings. Without such configuration information, many current
	1326	compilers would not work with the Boost libraries.</p>
	1327	<p>Centralizing configuration information in this header reduces the number of
	1328	files that must be modified when porting libraries to new platforms, or when
	1329	compilers are updated. Ideally, no other files would have to be modified when
	1330	porting to a new platform.</p>
	1331	<p>Configuration headers are controversial because some view them as condoning
	1332	broken compilers and encouraging non-standard subsets. Adding settings for
	1333	additional platforms and maintaining existing settings can also be a problem.
	1334	In other words, configuration headers are a necessary evil rather than a
	1335	desirable feature. The boost config.hpp policy is designed to minimize the
	1336	problems and maximize the benefits of a configuration header.</p>
	1337	<p>Note that:</p>
	1338	<ul>
	1339	<li>
	1340	Boost library implementers are not required to #include
	1341	<boost/config.hpp>, and are not required in any way to support compilers
	1342	that do not comply with the C++ Standard (ISO/IEC 14882).
	1343	<li>
	1344	If a library implementer wishes to support some non-conforming compiler, or to
	1345	support some platform specific feature, #include <boost/config.hpp> is
	1346	the preferred way to obtain configuration information not available from the
	1347	standard headers such as <climits>, etc.
	1348	<li>
	1349	If configuration information can be deduced from standard headers such as
	1350	<climits>, use those standard headers rather than
	1351	<boost/config.hpp>.
	1352	<li>
	1353	Boost files that use macros defined in <boost/config.hpp> should have
	1354	sensible, standard conforming, default behavior if the macro is not defined.
	1355	This means that the starting point for porting <boost/config.hpp> to a
	1356	new platform is simply to define nothing at all specific to that platform. In
	1357	the rare case where there is no sensible default behavior, an #error message
	1358	should describe the problem.
	1359	<li>
	1360	If a Boost library implementer wants something added to config.hpp, post a
	1361	request on the Boost mailing list. There is no guarantee such a request will be
	1362	honored; the intent is to limit the complexity of config.hpp.
	1363	<li>
	1364	The intent is to support only compilers which appear on their way to becoming
	1365	C++ Standard compliant, and only recent releases of those compilers at that.
	1366	<li>
	1367	The intent is not to disable mainstream features now well-supported by the
	1368	majority of compilers, such as namespaces, exceptions, RTTI, or templates.
	1369	</li>
	1370	</ul>
	1371	<h4><a name="defect_guidelines"></a>Adding New Defect Macros</h4>
	1372	<p>When you need to add a new defect macro - either to fix a problem with an
	1373	existing library, or when adding a new library - distil the issue down to a
	1374	simple test case, often at this point other (possibly better) workarounds may
	1375	become apparent. Secondly always post the test case code to the boost mailing
	1376	list and invite comments; remember that C++ is complex and that sometimes what
	1377	may appear a defect, may in fact turn out to be a problem with the authors
	1378	understanding of the standard.</p>
	1379	<p>When you name the macro, follow the BOOST_NO_SOMETHING naming convention, so
	1380	that it's obvious that this is a macro reporting a defect.</p>
	1381	<p>Finally, add the test program to the regression tests. You will need to place
	1382	the test case in a .ipp file with the following comments near the top:</p>
	1383	<pre>// MACRO: BOOST_NO_FOO
	1384	// TITLE: foo
	1385	// DESCRIPTION: If the compiler fails to support foo</pre>
	1386	<p>These comments are processed by the autoconf script, so make sure the format
	1387	follows the one given. The file should be named "boost_no_foo.ipp", where foo
	1388	is the defect description - try and keep the file name under the Mac 30
	1389	character filename limit though. You will also need to provide a function
	1390	prototype "int test()" that is declared in a namespace with the same name as
	1391	the macro, but in all lower case, and which returns zero on success:</p>
	1392	<pre>namespace boost_no_foo{
	1393
	1394	int test()
	1395	{
	1396	// test code goes here:
	1397	//
	1398	return 0;
	1399	}
	1400
	1401	}</pre>
	1402	<p>
	1403	Once the test code is in place, build and run the program "generate.cpp" that
	1404	you will find in the boost-root/libs/config/tools/ directory. This generates
	1405	two .cpp test files from the new test code, and adds the tests to the
	1406	regression test Jamfile, and the config_test.cpp test program. Finally add a
	1407	new entry to config_info.cpp so that the new macro gets printed out when that
	1408	program is run.</p>
	1409	<h4><a name="feature_guidelines"></a>Adding New Feature Test Macros</h4>
	1410	<p>When you need to add a macro that describes a feature that the standard does
	1411	not require, follow the convention for adding a new defect macro (above), but
	1412	call the macro BOOST_HAS_FOO, and name the test file "boost_has_foo.ipp". Try
	1413	not to add feature test macros unnecessarily, if there is a platform specific
	1414	macro that can already be used (for example _WIN32, __BEOS__, or __linux) to
	1415	identify the feature then use that. Try to keep the macro to a feature group,
	1416	or header name, rather than one specific API (for example BOOST_HAS_NL_TYPES_H
	1417	rather than BOOST_HAS_CATOPEN). If the macro describes a POSIX feature group,
	1418	then add boilerplate code to <a href="../../boost/config/suffix.hpp">boost/config/suffix.hpp</a>
	1419	to auto-detect the feature where possible (if you are wondering why we can't
	1420	use POSIX feature test macro directly, remember that many of these features can
	1421	be added by third party libraries, and are not therefore identified inside
	1422	<unistd.h>).</p>
	1423	<h4><a name="modify_guidelines"></a>Modifying the Boost Configuration Headers</h4>
	1424	<p>The aim of boost's configuration setup is that the configuration headers should
	1425	be relatively stable - a boost user should not have to recompile their code
	1426	just because the configuration for some compiler that they're not interested in
	1427	has changed. Separating the configuration into separate compiler/standard
	1428	library/platform sections provides for part of this stability, but boost
	1429	authors require some amount of restraint as well, in particular:</p>
	1430	<p><<a href="../../boost/config.hpp">boost/config.hpp</a>> should never
	1431	change, don't alter this file.</p>
	1432	<p><<a href="../../boost/config/user.hpp">boost/config/user.hpp</a>> is
	1433	included by default, don't add extra code to this file unless you have to. If
	1434	you do, please remember to update <a href="tools/configure.in">libs/config/tools/configure.in</a>
	1435	as well.</p>
	1436	<p><<a href="../../boost/config/suffix.hpp">boost/config/suffix.hpp</a>> is
	1437	always included so be careful about modifying this file as it breaks
	1438	dependencies for everyone. This file should include only "boilerplate"
	1439	configuration code, and generally should change only when new macros are added.</p>
	1440	<p><<a href="../../boost/config/select_compiler_config.hpp">boost/config/select_compiler_config.hpp</a>>,
	1441	<<a href="../../boost/config/select_platform_config.hpp">boost/config/select_platform_config.hpp</a>>
	1442	and <<a href="../../boost/config/select_stdlib_config.hpp">boost/config/select_stdlib_config.hpp</a>>
	1443	are included by default and should change only if support for a new
	1444	compiler/standard library/platform is added.</p>
	1445	<p>The compiler/platform/standard library selection code is set up so that unknown
	1446	platforms are ignored and assumed to be fully standards compliant - this gives
	1447	unknown platforms a "sporting chance" of working "as is" even without running
	1448	the configure script.</p>
	1449	<p>When adding or modifying the individual mini-configs, assume that future, as
	1450	yet unreleased versions of compilers, have all the defects of the current
	1451	version. Although this is perhaps unnecessarily pessimistic, it cuts down on
	1452	the maintenance of these files, and experience suggests that pessimism is
	1453	better placed than optimism here!</p>
	1454	<h2><a name="rationale"></a>Rationale</h2>
	1455	<p>The problem with many traditional "textbook" implementations of configuration
	1456	headers (where all the configuration options are in a single "monolithic"
	1457	header) is that they violate certain fundamental software engineering
	1458	principles which would have the effect of making boost more fragile, more
	1459	difficult to maintain and more difficult to use safely. You can find a
	1460	description of the principles from the <a href="http://www.objectmentor.com/publications/Principles%20and%20Patterns.PDF">
	1461	following article</a>.</p>
	1462	<h4>The problem</h4>
	1463	<p>Consider a situation in which you are concurrently developing on multiple
	1464	platforms. Then consider adding a new platform or changing the platform
	1465	definitions of an existing platform. What happens? Everything, and this does
	1466	literally mean everything, recompiles.. Isn't it quite absurd that adding a new
	1467	platform, which has absolutely nothing to do with previously existing
	1468	platforms, means that all code on all existing platforms needs to be
	1469	recompiled?</p>
	1470	<p>Effectively, there is an imposed physical dependency between platforms that
	1471	have nothing to do with each other. Essentially, the traditional solution
	1472	employed by configuration headers does not conform to the Open-Closed
	1473	Principle:</p>
	1474	<p><b><i>"A module should be open for extension but closed for modification."</i></b></p>
	1475	<p>Extending a traditional configuration header implies modifying existing code.</p>
	1476	<p>Furthermore, consider the complexity and fragility of the platform detection
	1477	code. What if a simple change breaks the detection on some minor platform? What
	1478	if someone accidentally or on purpose (as a workaround for some other problem)
	1479	defines some platform dependent macros that are used by the detection code? A
	1480	traditional configuration header is one of the most volatile headers of the
	1481	entire library, and more stable elements of Boost would depend on it. This
	1482	violates the Stable Dependencies Principle:</p>
	1483	<p><b><i>"Depend in the direction of stability."</i></b></p>
	1484	<p>After even a minor change to a traditional configuration header on one minor
	1485	platform, almost everything on every platform should be tested if we follow
	1486	sound software engineering practice.</p>
	1487	<p>Another important issue is that it is not always possible to submit changes to
	1488	<boost/config.hpp>. Some boost users are currently working on platforms
	1489	using tools and libraries that are under strict Non-Disclosure Agreements. In
	1490	this situation it is impossible to submit changes to a traditional monolithic
	1491	configuration header, instead some method by which the user can insert their
	1492	own configuration code must be provided.</p>
	1493	<h4>The solution</h4>
	1494	<p>The approach taken by boost's configuration headers is to separate
	1495	configuration into three orthogonal parts: the compiler, the standard library
	1496	and the platform. Each compiler/standard library/platform gets its own
	1497	mini-configuration header, so that change to one compiler's configuration (for
	1498	example) does not effect other compilers. In addition there are measures that
	1499	can be taken both to omit the compiler/standard library/platform detection code
	1500	(so that adding support to a new platform does not break dependencies), or to
	1501	freeze the configuration completely; providing almost complete protection
	1502	against dependency changes.</p>
	1503	<h2><a name="Acknowledgements"></a>Acknowledgements</h2>
	1504	<p>Beman Dawes provided the original config.hpp and part of this document. Vesa
	1505	Karvonen provided a description of the principles (see <a href="#rationale">rationale</a>)
	1506	and put together an early version of the current configuration setup. John
	1507	Maddock put together the configuration current code, the test programs, the
	1508	configuration script and the reference section of this document. Numerous boost
	1509	members, past and present, have contributed fixes to boost's configuration.</p>
	1510	<p> </p>
	1511	<hr>
	1512	<p>© Beman Dawes 2001</p>
	1513	<p>© Vesa Karvonen 2001</p>
	1514	<p>© John Maddock 2001</p>
	1515	<p> </p>
	1516	<p> </p>
	1517	<p> </p>
	1518	<p> </p>
	1519	<p> </p>
	1520	</body>
	1521	</html>

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