[/
    Boost.Config

    Copyright (c) 2001 Beman Dawes
    Copyright (c) 2001 Vesa Karvonen
    Copyright (c) 2001 John Maddock

    Distributed under the Boost Software License, Version 1.0.
    (See accompanying file LICENSE_1_0.txt or copy at
    http://www.boost.org/LICENSE_1_0.txt)
]



[section Boost Macro Reference]

[#config_defects]

[section Macros that describe C++03 defects]

The following macros all describe features that are required by the C++03 standard,
if one of the following macros is defined, then it represents a defect in the
compiler's conformance with the 2003 standard.


[table
[[Macro        ][Section     ][ Description          ]]


[[`BOOST_BCB_PARTIAL_SPECIALIZATION_BUG`][Compiler][
The compiler exhibits certain partial specialisation bug - probably Borland
C++ Builder specific.
]]
[[`BOOST_FUNCTION_SCOPE_USING_DECLARATION_BREAKS_ADL`][Compiler][
Argument dependent lookup fails if there is a using declaration for the
symbol being looked up in the current scope.  For example, using
`boost::get_pointer`; prevents ADL from finding overloads of `get_pointer`
in namespaces nested inside boost (but not elsewhere).  Probably
Borland specific.
]]
[[`BOOST_NO_ADL_BARRIER`][Compiler][
The compiler locates and searches namespaces that it should /*not*/ in fact 
search when performing argument dependent lookup.
]]
[[`BOOST_NO_ARGUMENT_DEPENDENT_LOOKUP`][Compiler][
Compiler does not implement argument-dependent lookup (also named
Koenig lookup); see std::3.4.2 \[basic.koenig.lookup\]
]]
[[`BOOST_NO_AUTO_PTR`][Standard library][
If the compiler / library supplies non-standard or broken `std::auto_ptr`.
]]
[[`BOOST_NO_COMPLETE_VALUE_INITIALIZATION`][Compiler][ 
Compiler has not completely implemented value-initialization. 
See also [@../../../utility/value_init.htm#compiler_issues The Utility\/Value Init docs] 
]] 
[[`BOOST_NO_CTYPE_FUNCTIONS`][Platform][
The Platform does not provide functions for the character-classifying
operations `<ctype.h>` and `<cctype>`, only macros.
]]
[[`BOOST_NO_CV_SPECIALIZATIONS`][Compiler][
If template specialisations for cv-qualified types conflict with a
specialisation for a cv-unqualififed type.
]]
[[`BOOST_NO_CV_VOID_SPECIALIZATIONS`][Compiler][
If template specialisations for cv-void types conflict with a specialisation
for void.
]]
[[`BOOST_NO_CWCHAR`][Platform][
The Platform does not provide `<wchar.h>` and `<cwchar>`.
]]
[[`BOOST_NO_CWCTYPE`][Platform][
The Platform does not provide `<wctype.h>` and `<cwctype>`.
]]
[[`BOOST_NO_FENV_H`][Platform, Standard library][
The C standard library doesn't provide `<fenv.h>`. [@../../../../boost/detail/fenv.hpp
`<boost/detail/fenv.hpp>`] should be included instead of `<fenv.h>` for maximum
portability on platforms which do provide `<fenv.h>`. 
]]
[[`BOOST_NO_DEPENDENT_NESTED_DERIVATIONS`][Compiler][
The compiler fails to compile a nested class that has a dependent base class:
``
template<typename T>
struct foo : {
   template<typename U>
   struct bar : public U {};
``
};
]]
[[`BOOST_NO_DEPENDENT_TYPES_IN_TEMPLATE_VALUE_PARAMETERS`][Compiler][
Template value parameters cannot have a dependent type, for example:
``
template<class T, typename T::type value> 
class X { ... };
``
]]
[[`BOOST_NO_EXCEPTION_STD_NAMESPACE`][Standard Library][
The standard library does not put some or all of the contents of
`<exception>` in namespace std.
]]
[[`BOOST_NO_EXCEPTIONS`][Compiler][
The compiler does not support exception handling (this setting is typically
required by many C++ compilers for embedded platforms). Note that there is
no requirement for boost libraries to honor this configuration setting -
indeed doing so may be impossible in some cases. Those libraries that do
honor this will typically abort if a critical error occurs - you have been
warned!
]]
[[`BOOST_NO_FUNCTION_TEMPLATE_ORDERING`][Compiler][
The compiler does not perform function template ordering or its function
template ordering is incorrect.
``
// #1
template<class T> void f(T);

// #2
template<class T,class U> void f(T(*)(U));

void bar(int);

f(&bar); // should choose #2.
``
]]
[[`BOOST_NO_INCLASS_MEMBER_INITIALIZATION`][Compiler][
Compiler violates std::9.4.2/4.
]]
[[`BOOST_NO_INTRINSIC_WCHAR_T`][Compiler][
The C++ implementation does not provide `wchar_t`, or it is really a synonym
for another integral type. Use this symbol to decide whether it is appropriate
to explicitly specialize a template on `wchar_t` if there is already a
specialization for other integer types.
]]
[[`BOOST_NO_IOSFWD`][std lib][
The standard library lacks `<iosfwd>`.
]]
[[`BOOST_NO_IOSTREAM`][std lib][
The standard library lacks `<iostream>`, `<istream>` or `<ostream>`.
]]
[[`BOOST_NO_IS_ABSTRACT`][Compiler][
The C++ compiler does not support SFINAE with abstract types, this is covered
by __CORE_LANGUAGE_DR337__, but is not part of the current standard.  Fortunately
most compilers that support SFINAE also support this DR.  See also BOOST_NO_SFINAE and BOOST_NO_SFINAE_EXPR
]]
[[`BOOST_NO_LIMITS`][Standard library][
The C++ implementation does not provide the `<limits>` header. Never check for
this symbol in library code; always include `<boost/limits.hpp>`, which
guarantees to provide `std::numeric_limits`.
]]
[[`BOOST_NO_CXX11_NUMERIC_LIMITS`][Standard library][
C++11 additions to `std::numeric_limits` are not available for use.
`static function numeric_limits<T>::lowest()` the lowest finite value representable by the numeric type.
`static int const max_digits10` the number of decimal digits that are required to make sure that two distinct values of the type have distinct decimal representations.
`template<> class numeric_limits<char16_t>;`, see also `BOOST_NO_CXX11_CHAR16_T`, 
`template<> class numeric_limits<char32_t>;` see also `BOOST_NO_CXX11_CHAR32_T`.
Replaces BOOST_NO_NUMERIC_LIMITS_LOWEST.
]]
[[`BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS`][Standard library][
Constants such as `numeric_limits<T>::is_signed` are not available for use
at compile-time.
]]
[[`BOOST_NO_LONG_LONG_NUMERIC_LIMITS`][Standard library][
There is no specialization for `numeric_limits<long long>` and
`numeric_limits<unsigned long long>`. `<boost/limits.hpp>` will then add these
specializations as a standard library "fix" only if the compiler supports the
`long long` datatype.
]]
[[`BOOST_NO_MEMBER_FUNCTION_SPECIALIZATIONS`][Compiler][
The compiler does not support the specialization of individual member
functions of template classes.
]]
[[`BOOST_NO_MEMBER_TEMPLATE_KEYWORD`][Compiler][
If the compiler supports member templates, but not the template keyword
when accessing member template classes.
]]
[[`BOOST_NO_MEMBER_TEMPLATE_FRIENDS`][Compiler][
Member template friend syntax (`template<class P> friend class frd;`)
described in the C++ Standard, 14.5.3, not supported.
]]
[[`BOOST_NO_MEMBER_TEMPLATES`][Compiler][
Member template functions not fully supported.
]]
[[`BOOST_NO_MS_INT64_NUMERIC_LIMITS`][Standard library][
There is no specialization for `numeric_limits<__int64>` and
`numeric_limits<unsigned __int64>`. `<boost/limits.hpp>` will then add these
specializations as a standard library "fix", only if the compiler supports
the `__int64` datatype.
]]
[[`BOOST_NO_NESTED_FRIENDSHIP`][Compiler][
Compiler doesn't allow a nested class to access private members of its
containing class. Probably Borland/CodeGear specific.
]]
[[`BOOST_NO_OPERATORS_IN_NAMESPACE`][Compiler][
Compiler requires inherited operator friend functions to be defined at
namespace scope, then using'ed to boost. Probably GCC specific. See
[@../../../../boost/operators.hpp `<boost/operators.hpp>`] for example.
]]
[[`BOOST_NO_PARTIAL_SPECIALIZATION_IMPLICIT_DEFAULT_ARGS`][Compiler][
The compiler does not correctly handle partial specializations
which depend upon default arguments in the primary template.
]]
[[`BOOST_NO_POINTER_TO_MEMBER_CONST`][Compiler][
The compiler does not correctly handle pointers to const member functions,
preventing use of these in overloaded function templates. See
[@../../../../boost/functional.hpp `<boost/functional.hpp>`] for example.
]]
[[`BOOST_NO_POINTER_TO_MEMBER_TEMPLATE_PARAMETERS`][Compiler][
Pointers to members don't work when used as template parameters.
]]
[[`BOOST_NO_PRIVATE_IN_AGGREGATE`][Compiler][
The compiler misreads 8.5.1, treating classes as non-aggregate if they
contain private or protected member functions.
]]
[[`BOOST_NO_RESTRICT_REFERENCES`][Compiler][
Compiler-specific `restrict` keyword can not be applied to references.
]]
[[`BOOST_NO_RTTI`][Compiler][
The compiler may (or may not) have the typeid operator, but RTTI on the dynamic type
of an object is not supported.
]]
[[`BOOST_NO_SFINAE`][Compiler][
The compiler does not support the "Substitution Failure Is Not An Error"
meta-programming idiom.  This is the lightweight pre-C++11 version of SFINAE.
]]
[[`BOOST_NO_SFINAE_EXPR`][Compiler][
The compiler does not support usage of SFINAE with arbitrary expressions.  This is the
post-C++11 SFINAE, but excludes a few specific corner cases, see also BOOST_NO_CXX11_SFINAE_EXPR.
]]
[[`BOOST_NO_STD_ALLOCATOR`][Standard library][
The C++ standard library does not provide a standards conforming
`std::allocator`.
]]
[[`BOOST_NO_STD_DISTANCE`][Standard library][
The platform does not have a conforming version of `std::distance`.
]]
[[`BOOST_NO_STD_ITERATOR`][Standard library][
The C++ implementation fails to provide the `std::iterator` class.  
Note that post C++17, this macro is re-purposed to indicate that std::iterator has been removed or deprecated.
]]
[[`BOOST_NO_STD_ITERATOR_TRAITS`][Standard library][
The compiler does not provide a standard compliant implementation of
`std::iterator_traits`. Note that the compiler may still have a
non-standard implementation.
]]
[[`BOOST_NO_STD_LOCALE`][Standard library][
The standard library lacks `std::locale`.
]]
[[`BOOST_NO_STD_MESSAGES`][Standard library][
The standard library lacks a conforming `std::messages` facet.
]]
[[`BOOST_NO_STD_MIN_MAX`][Standard library][
The C++ standard library does not provide the `min()` and `max()` template
functions that should be in `<algorithm>`.
]]
[[`BOOST_NO_STD_OUTPUT_ITERATOR_ASSIGN`][Standard library][
Defined if the standard library's output iterators are not assignable.
]]
[[`BOOST_NO_STD_TYPEINFO`][Standard library][
The <typeinfo> header declares `type_info` in the global namespace instead of namespace std.
]]
[[`BOOST_NO_STD_USE_FACET`][Standard library][
The standard library lacks a conforming `std::use_facet`.
]]
[[`BOOST_NO_STD_WSTREAMBUF`][Standard library][
The standard library's implementation of `std::basic_streambuf<wchar_t>`
is either missing, incomplete, or buggy.
]]
[[`BOOST_NO_STD_WSTRING`][Standard library][
The standard library lacks `std::wstring`.
]]
[[`BOOST_NO_STDC_NAMESPACE`][Compiler, Platform][
The contents of C++ standard headers for C library functions
(the `<c...>` headers) have not been placed in namespace std. This test is
difficult - some libraries "fake" the std C functions by adding using
declarations to import them into namespace std, unfortunately they don't
necessarily catch all of them...
]]
[[`BOOST_NO_STRINGSTREAM`][Standard library][
The C++ implementation does not provide the `<sstream>` header.
]]
[[`BOOST_NO_SWPRINTF`][Platform][
The platform does not have a conforming version of `swprintf`.
]]
[[`BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION`][Compiler][
Class template partial specialization (14.5.4 \[temp.class.spec\]) not
supported.
]]
[[`BOOST_NO_TEMPLATED_IOSTREAMS`][Standard library][
The standard library does not provide templated iostream classes.
]]
[[`BOOST_NO_TEMPLATED_ITERATOR_CONSTRUCTORS`][Standard library][
The standard library does not provide templated iterator constructors
for its containers.
]]
[[`BOOST_NO_TEMPLATE_TEMPLATES`][Compiler][
The compiler does not support template template parameters.
]]
[[`BOOST_NO_TYPEID`][Compiler][
The compiler does not support the typeid operator at all.
]]
[[`BOOST_NO_TYPENAME_WITH_CTOR`][Compiler][
The typename keyword cannot be used when creating a temporary of a
Dependent type.
]]
[[`BOOST_NO_UNREACHABLE_RETURN_DETECTION`][Compiler][
If a return is unreachable, then no return statement should be required,
however some compilers insist on it, while other issue a bunch of warnings
if it is in fact present.
]]
[[`BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE`][Compiler][
The compiler will not accept a using declaration that brings a function
from a typename used as a base class into a derived class if functions of
the same name are present in the derived class.
]]
[[`BOOST_NO_USING_TEMPLATE`][Compiler][
The compiler will not accept a using declaration that imports a template
class or function from another namespace. Originally a Borland specific
problem with imports to/from the global namespace, extended to MSVC6
which has a specific issue with importing template classes (but not
functions).
]]
[[`BOOST_NO_VOID_RETURNS`][Compiler][
The compiler does not allow a void function to return the result of calling
another void function.
``
void f() {}
void g() { return f(); }
``
]]
]

[endsect]

[#config_features]


[section Macros that describe optional features]

The following macros describe features that are not required by the C++
standard. The macro is only defined if the feature is present.


[table
[[Macro       ][Section        ][Description       ]]

[[`BOOST_HAS_BETHREADS`][Platform][
The platform supports BeOS style threads.
]]
[[`BOOST_HAS_CLOCK_GETTIME`][Platform][
The platform has the POSIX API `clock_gettime`.
]]
[[`BOOST_HAS_DIRENT_H`][Platform][
The platform has the POSIX header `<dirent.h>`.
]]
[[`BOOST_HAS_EXPM1`][Platform][
The platform has the functions `expm1`, `expm1f` and `expm1l` in `<math.h>`
]]
[[`BOOST_HAS_FLOAT128`][Compiler][
The compiler has `__float128` as a native type which is distinct
from all the regular C++ floating point types.]]
[[`BOOST_HAS_FTIME`][Platform][
The platform has the Win32 API type FTIME.
]]
[[`BOOST_HAS_GETSYSTEMTIMEASFILETIME`][Platform][
The platform has the Win32 API GetSystemTimeAsFileTime.
]]
[[`BOOST_HAS_GETTIMEOFDAY`][Platform][
The platform has the POSIX API `gettimeofday`.
]]
[[`BOOST_HAS_HASH`][Standard library][
The C++ implementation provides the (SGI) hash_set and hash_map classes.
When defined, `BOOST_HASH_SET_HEADER` and `BOOST_HASH_LIST_HEADER` will contain
the names of the header needed to access hash_set and hash_map;
`BOOST_STD_EXTENSION_NAMESPACE` will provide the namespace in which the two
class templates reside.
]]
[[`BOOST_HAS_INT128`][Compiler][
The compiler has `__int128` and `unsigned __int128` as native types which are distinct
from all the regular C++ integer types.]]
[[`BOOST_HAS_LOG1P`][Platform][
The platform has the functions `log1p`, `log1pf` and `log1pl` in `<math.h>`.
]]
[[`BOOST_HAS_MACRO_USE_FACET`][Standard library][
The standard library lacks a conforming `std::use_facet`, but has a macro
`_USE(loc, Type)` that does the job. This is primarily for the Dinkumware
std lib.
]]
[[`BOOST_HAS_MS_INT64`][Compiler][
The compiler supports the `__int64` data type.
]]
[[`BOOST_HAS_NANOSLEEP`][Platform][
The platform has the POSIX API nanosleep.
]]
[[`BOOST_HAS_NL_TYPES_H`][Platform][
The platform has an `<nl_types.h>`.
]]
[[`BOOST_HAS_NRVO`][Compiler][
Indicated that the compiler supports the named return value optimization
(NRVO). Used to select the most efficient implementation for some function.
See [@../../../../boost/operators.hpp `<boost/operators.hpp>`] for example.
]]
[[`BOOST_HAS_PARTIAL_STD_ALLOCATOR`][Standard Library][
The standard library has a partially conforming `std::allocator` class, but
without any of the member templates.
]]
[[`BOOST_HAS_PRAGMA_ONCE`][Compiler][
The compiler recognizes the `#pragma once` directive which tells that the
containing header should be included only once while preprocessing the
current translation unit. The pragma may improve compile times of large projects
with some compilers.
]]
[[`BOOST_HAS_PRAGMA_DETECT_MISMATCH`][Compiler][
The compiler recognizes the `#pragma detect_mismatch("name", "value")` directive which tells that the
link stage should be terminated with error if values for provided `"name"` missmatch.
This pragma may be a help in preventing ODR violations and ensuring that different modules
are compiled with same flags.
]]

[[`BOOST_HAS_PTHREAD_DELAY_NP`][Platform][
The platform has the POSIX API `pthread_delay_np`.
]]
[[`BOOST_HAS_PTHREAD_MUTEXATTR_SETTYPE`][Platform][
The platform has the POSIX API `pthread_mutexattr_settype`.
]]
[[`BOOST_HAS_PTHREAD_YIELD`][Platform][
The platform has the POSIX API `pthread_yield`.
]]
[[`BOOST_HAS_PTHREADS`][Platform][
The platform support POSIX style threads.
]]
[[`BOOST_HAS_SCHED_YIELD`][Platform][
The platform has the POSIX API `sched_yield`.
]]
[[`BOOST_HAS_SGI_TYPE_TRAITS`][Compiler, Standard library][
The compiler has native support for SGI style type traits.
]]
[[`BOOST_HAS_STDINT_H`][Platform][
The platform has a `<stdint.h>`
]]
[[`BOOST_HAS_SLIST`][Standard library][
The C++ implementation provides the (SGI) slist class. When defined,
`BOOST_SLIST_HEADER` will contain the name of the header needed to access
`slist` and `BOOST_STD_EXTENSION_NAMESPACE` will provide the namespace in
which `slist` resides.
]]
[[`BOOST_HAS_STLP_USE_FACET`][Standard library][
The standard library lacks a conforming `std::use_facet`, but has a workaround
class-version that does the job. This is primarily for the STLport std lib.
]]
[[`BOOST_HAS_TR1_ARRAY`][Standard library][
The library has a TR1 conforming version of `<array>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_ARRAY.
]]
[[`BOOST_HAS_TR1_COMPLEX_OVERLOADS`][Standard library][
The library has a version of `<complex>` that supports passing scalars to the
complex number algorithms.
]]
[[`BOOST_HAS_TR1_COMPLEX_INVERSE_TRIG`][Standard library][
The library has a version of `<complex>` that includes the new inverse trig
functions from TR1.
]]
[[`BOOST_HAS_TR1_REFERENCE_WRAPPER`][Standard library][
The library has TR1 conforming reference wrappers in `<functional>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_FUNCTIONAL.
]]
[[`BOOST_HAS_TR1_RESULT_OF`][Standard library][
The library has a TR1 conforming result_of template in `<functional>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_FUNCTIONAL.
]]
[[`BOOST_HAS_TR1_MEM_FN`][Standard library][
The library has a TR1 conforming mem_fn function template in `<functional>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_FUNCTIONAL.
]]
[[`BOOST_HAS_TR1_BIND`][Standard library][
The library has a TR1 conforming bind function template in `<functional>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_FUNCTIONAL.
]]
[[`BOOST_HAS_TR1_FUNCTION`][Standard library][
The library has a TR1 conforming function class template in `<functional>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_FUNCTIONAL.
]]
[[`BOOST_HAS_TR1_HASH`][Standard library][
The library has a TR1 conforming hash function template in `<functional>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_FUNCTIONAL.
]]
[[`BOOST_HAS_TR1_SHARED_PTR`][Standard library][
The library has a TR1 conforming `shared_ptr` class template in `<memory>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_SMART_PTR.
]]
[[`BOOST_HAS_TR1_RANDOM`][Standard library][
The library has a TR1 conforming version of `<random>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_RANDOM.
]]
[[`BOOST_HAS_TR1_REGEX`][Standard library][
The library has a TR1 conforming version of `<regex>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_REGEX.
]]
[[`BOOST_HAS_TR1_TUPLE`][Standard library][
The library has a TR1 conforming version of `<tuple>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_TUPLE.
]]
[[`BOOST_HAS_TR1_TYPE_TRAITS`][Standard library][
The library has a TR1 conforming version of `<type_traits>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_TYPE_TRAITS.
]]
[[`BOOST_HAS_TR1_UTILITY`][Standard library][
The library has the TR1 additions to `<utility>` (tuple interface to `std::pair`).  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_TUPLE.
]]
[[`BOOST_HAS_TR1_UNORDERED_MAP`][Standard library][
The library has a TR1 conforming version of `<unordered_map>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_UNORDERED_MAP.
]]
[[`BOOST_HAS_TR1_UNORDERED_SET`][Standard library][
The library has a TR1 conforming version of `<unordered_set>`.  This macro is only guaranteed
to be defined after including one of the headers from Boost.TR1.  Further this macro
is now deprecated in favour of BOOST_NO_CXX11_HDR_UNORDERED_SET.
]]
[[`BOOST_HAS_TR1`][Standard library][
Implies all the other `BOOST_HAS_TR1_*` macros should be set.
]]
[[`BOOST_HAS_THREADS`][Platform, Compiler][
Defined if the compiler, in its current translation mode, supports multiple
threads of execution.
]]
[[`BOOST_HAS_TWO_ARG_USE_FACET`][Standard library][
The standard library lacks a conforming std::use_facet, but has a two
argument version that does the job. This is primarily for the Rogue Wave
std lib.
]]
[[`BOOST_HAS_UNISTD_H`][Platform][
The Platform provides `<unistd.h>`.
]]
[[`BOOST_HAS_WINTHREADS`][Platform][
The platform supports MS Windows style threads.
]]
[[`BOOST_MSVC_STD_ITERATOR`][Standard library][
Microsoft's broken version of `std::iterator` is being used. This implies that
`std::iterator` takes no more than two template parameters.
]]
[[`BOOST_MSVC6_MEMBER_TEMPLATES`][Compiler][
Microsoft Visual C++ 6.0 has enough member template idiosyncrasies
(being polite) that `BOOST_NO_MEMBER_TEMPLATES` is defined for this compiler.
`BOOST_MSVC6_MEMBER_TEMPLATES` is defined to allow compiler specific workarounds.
This macro gets defined automatically if `BOOST_NO_MEMBER_TEMPLATES` is not
defined - in other words this is treated as a strict subset of the features
required by the standard.
]]
[[`BOOST_HAS_STDINT_H`][Platform][
There are no 1998 C++ Standard headers `<stdint.h>` or `<cstdint>`, although the
1999 C Standard does include `<stdint.h>`. If `<stdint.h>` is present,
`<boost/stdint.h>` can make good use of it, so a flag is supplied (signalling
presence; thus the default is not present, conforming to the current C++
standard).
]]
]

[endsect]

[section Macros that describe possible C++ future features]

The following macros describe features that may be included in some future
ISO C++ standard, but have not yet been approved for inclusion in the language.


[table
[[Macro     ][Description     ]]

[[`BOOST_HAS_CONCEPTS`][
The compiler supports  concepts.
]]
]

[endsect]

[section Macros that describe C++11 features not supported]

The following macros describe features in the 2011 ISO C++ standard, formerly known as C++0x,
that are not yet supported by a particular compiler or library.

[table
[[Macro     ][Description     ]]

[[`BOOST_NO_CXX11_ADDRESSOF`][The standard library header <memory> has no working std::addressof.]]
[[`BOOST_NO_CXX11_ALIGNAS`][The compiler does not support the `alignas` keyword.]]
[[`BOOST_NO_CXX11_ALLOCATOR`][The standard library does not provide a C++11 version of `std::allocator` in <memory>.]]
[[`BOOST_NO_CXX11_ATOMIC_SMART_PTR`][The standard library <memory> does not support atomic smart pointer operations.]]
[[`BOOST_NO_CXX11_AUTO_DECLARATIONS`][The compiler does not support
type deduction for variables declared with the `auto` keyword (`auto var = ...;`).
]]
[[`BOOST_NO_CXX11_AUTO_MULTIDECLARATIONS`][The compiler does not support
type deduction for multiple variables declared with the `auto` keyword (`auto var = ..., *ptr = ...;`).
]]
[[`BOOST_NO_CXX11_CHAR16_T`][The compiler does not support
type `char16_t`. 
]]
[[`BOOST_NO_CXX11_CHAR32_T`][The compiler does not support 
type `char32_t`. 
]]
[[`BOOST_NO_CXX11_CONSTEXPR`][The compiler does not support 
`constexpr`. 
]]
[[`BOOST_NO_CXX11_DECLTYPE`][The compiler does not support 
`decltype`. 
]]
[[`BOOST_NO_CXX11_DECLTYPE_N3276`][The compiler does not support the extension to
`decltype` described in [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3276.pdf N3276],
accepted in Madrid, March 2011.
]]
[[`BOOST_NO_CXX11_DELETED_FUNCTIONS`][The compiler does not support
deleted (`= delete`) functions.
]]
[[`BOOST_NO_CXX11_DEFAULTED_FUNCTIONS`][The compiler does not support
defaulted (`= default`) functions.
]]
[[`BOOST_NO_CXX11_DEFAULTED_MOVES`][The compiler does not support
defaulted move constructor or assignment. Other defaulted functions may still be supported.
]]
[[`BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS`][The compiler does not support 
explicit conversion operators (`explicit operator T()`).
]] 
[[`BOOST_NO_CXX11_EXTERN_TEMPLATE`][The compiler does not support 
explicit instantiation forward declarations for templates (`extern template ...`).
]]
[[`BOOST_NO_CXX11_FINAL`][The compiler does not support the C++ class-virt-specifier final.
]]
[[`BOOST_NO_CXX11_FIXED_LENGTH_VARIADIC_TEMPLATE_EXPANSION_PACKS`][The compiler does not support
expanding a variadic template parameter pack into a template containing one or more
fixed arguments]]
[[`BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS`][The compiler does not support
default template arguments for function templates.
]]
[[`BOOST_NO_CXX11_HDR_ATOMIC`][The standard library does not provide header <atomic>.]]
[[`BOOST_NO_CXX11_HDR_ARRAY`][The standard library does not provide header <array>.]]
[[`BOOST_NO_CXX11_HDR_CHRONO`][The standard library does not provide header <chrono>.]]
[[`BOOST_NO_CXX11_HDR_CODECVT`][The standard library does not provide header <codecvt>.]]
[[`BOOST_NO_CXX11_HDR_CONDITION_VARIABLE`][The standard library does not provide header <condition_variable>.]]
[[`BOOST_NO_CXX11_HDR_EXCEPTION`][The standard library does not provide a C++11 compatible version of <exception>.]]
[[`BOOST_NO_CXX11_HDR_FORWARD_LIST`][The standard library does not provide header <forward_list>.]]
[[`BOOST_NO_CXX11_HDR_FUNCTIONAL`][The standard library does not provide a C++11 compatible version of <functional>.]]
[[`BOOST_NO_CXX11_HDR_FUTURE`][The standard library does not provide header <future>.]]
[[`BOOST_NO_CXX11_HDR_INITIALIZER_LIST`][The standard library does not provide header <initializer_list>.]]
[[`BOOST_NO_CXX11_HDR_MUTEX`][The standard library does not provide header <mutex>.]]
[[`BOOST_NO_CXX11_HDR_RANDOM`][The standard library does not provide header <random>.]]
[[`BOOST_NO_CXX11_HDR_RATIO`][The standard library does not provide header <ratio>.]]
[[`BOOST_NO_CXX11_HDR_REGEX`][The standard library does not provide header <regex>.]]
[[`BOOST_NO_CXX11_HDR_SYSTEM_ERROR`][The standard library does not provide header <system_error>.]]
[[`BOOST_NO_CXX11_HDR_THREAD`][The standard library does not provide header <thread>.]]
[[`BOOST_NO_CXX11_HDR_TUPLE`][The standard library does not provide header <tuple>.]]
[[`BOOST_NO_CXX11_HDR_TYPEINDEX`][The standard library does not provide header <typeindex>.]]
[[`BOOST_NO_CXX11_HDR_TYPE_TRAITS`][The standard library does not provide header <type_traits>.]]
[[`BOOST_NO_CXX11_HDR_UNORDERED_MAP`][The standard library does not provide header <unordered_map>.]]
[[`BOOST_NO_CXX11_HDR_UNORDERED_SET`][The standard library does not provide header <unordered_set>.]]

[[`BOOST_NO_CXX11_INLINE_NAMESPACES`][The compiler does not support inline namespaces.]]
[[`BOOST_NO_CXX11_LAMBDAS`][The compiler does not support Lambdas. 
]]
[[`BOOST_NO_CXX11_LOCAL_CLASS_TEMPLATE_PARAMETERS`][The compiler does not allow to
pass local classes as template parameters (this macro intentionally does not
control passing of unnamed types as template parameters, see also
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm N2657]).
]]
[[`BOOST_NO_CXX11_NON_PUBLIC_DEFAULTED_FUNCTIONS`][The compiler does not support
defaulted (`= default`) functions in access control sections other than `public`. Public defaulted
functions may still be supported, as indicated by `BOOST_NO_CXX11_DEFAULTED_FUNCTIONS`. Some
compilers implementing an early draft of the C++11 standard (in particular, incorporating
[@http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#906 DR906]) are susceptible to this problem.
]]
[[`BOOST_NO_CXX11_NOEXCEPT`][The compiler does not support `noexcept`. 
]]
[[`BOOST_NO_CXX11_NULLPTR`][The compiler does not support `nullptr`. 
]]
[[`BOOST_NO_CXX11_NUMERIC_LIMITS`][The standard library `<limits>` header does
not support the C++11 version of `numeric_limits`. 
]]
[[`BOOST_NO_CXX11_OVERRIDE`][The compiler does not support `override`.
]]
[[`BOOST_NO_CXX11_POINTER_TRAITS`][The standard library does not provide a
C++11 version of `std::pointer_traits` in <memory>.]]
[[`BOOST_NO_CXX11_RANGE_BASED_FOR`][The compiler does not support
range-based for statements. 
]]
[[`BOOST_NO_CXX11_RAW_LITERALS`][The compiler does not support
raw string literals. 
]]
[[`BOOST_NO_CXX11_REF_QUALIFIERS`][The compiler does not support
ref-qualifiers on member functions as described in 
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2439.htm N2439]. 
]]
[[`BOOST_NO_CXX11_RVALUE_REFERENCES`][The compiler does not support
r-value references. 
]]
[[`BOOST_NO_CXX11_SCOPED_ENUMS`][The compiler does not support
scoped enumerations (`enum class`). 
]]
[[`BOOST_NO_CXX11_SFINAE_EXPR`][The compiler does not support
usage of C++11 SFINAE with arbitrary expressions.  Use this macro only if you
are using all of the features of SFINAE including substitution-failure-on-private-member-access.  
Otherwise use BOOST_NO_SFINAE_EXPR or BOOST_NO_SFINAE which get defined for fewer compilers.
]]
[[`BOOST_NO_CXX11_SMART_PTR`][The standard library header <memory> has no shared_ptr and unique_ptr.]]
[[`BOOST_NO_CXX11_STATIC_ASSERT`][The compiler does not support
`static_assert`. 
]]
[[`BOOST_NO_CXX11_STD_ALIGN`][The standard library header <memory> has no working std::align.]]
[[`BOOST_NO_CXX11_STD_UNORDERED`][The standard library does not support
<unordered_map> and <unordered_set>. 
]]
[[`BOOST_NO_CXX11_TEMPLATE_ALIASES`][The compiler does not support template aliases. 
]]
[[`BOOST_NO_CXX11_THREAD_LOCAL`][The compiler does not support the `thread_local` storage specifier. 
]]
[[`BOOST_NO_CXX11_TRAILING_RESULT_TYPES`][The compiler does not support the new function result type
specification syntax (e.g. `auto foo(T) -> T;`).]]
[[`BOOST_NO_CXX11_UNICODE_LITERALS`][The compiler does not support
Unicode (`u8`, `u`, `U`) literals. 
]]
[[`BOOST_NO_CXX11_UNIFIED_INITIALIZATION_SYNTAX`][The compiler does not support
the [@http://en.wikipedia.org/wiki/C%2B%2B0x#Uniform_initialization C++11 Unified Initialization Syntax].
]]
[[`BOOST_NO_CXX11_UNRESTRICTED_UNION`][The compiler does not support an unrestricted union. This is
a union that may contain static data as well as user-defined member data with non-trivial special
member functions.
]]
[[`BOOST_NO_CXX11_USER_DEFINED_LITERALS`][The compiler does not support user defined literals. 
]]
[[`BOOST_NO_CXX11_VARIADIC_TEMPLATES`][The compiler does not support
variadic templates.
]]
[[`BOOST_NO_CXX11_VARIADIC_MACROS`][The compiler does not support
variadic macros.
]]
[[`BOOST_NO_LONG_LONG`][The compiler does not support `long long`.
]]
]

[endsect]

[#config_11_for_03]

[section Macros that allow use of C++11 features with C++03 compilers]

The following macros allow use of C++11 features even with compilers that do not yet
provide compliant C++11 support.

[table
[[Macro        ][ Description          ]]

[[`BOOST_ALIGNMENT(X)`, `BOOST_NO_ALIGNMENT`][
Some compilers don't support the `alignas` keyword but provide other means to specify alignment
(usually, through compiler-specific attributes). The macro `BOOST_ALIGNMENT(X)` will expand to the `alignas(X)`
keyword if the compiler supports it or to some compiler-specific attribute to achieve the specified alignment.
If no such compiler-specific attribute is known then `BOOST_ALIGNMENT(X)` will expand to nothing and
`BOOST_NO_ALIGNMENT` will be defined. Unlike native `alignas`, `X` must always be a compile-time integer constant.
The macro can be used to specify alignment of types and data:
``
  struct BOOST_ALIGNMENT(16) my_data
  {
      char c[16];
  };
  BOOST_ALIGNMENT(8) int arr[32];
``
]]
[[`BOOST_CONSTEXPR`][
Some compilers don't support the use of `constexpr`. This macro expands to nothing on those compilers, and `constexpr`
elsewhere. For example, when defining a constexpr function or constructor replace:
``
  constexpr tuple();
``
with:
``
  BOOST_CONSTEXPR tuple();
``
]]
[[`BOOST_CONSTEXPR_OR_CONST`][
Some compilers don't support the use of `constexpr`. This macro expands to `const` on those compilers, and `constexpr`
elsewhere. For example, when defining const expr variables replace:
``
  static constexpr UIntType xor_mask = a;
``
with:
``
  static BOOST_CONSTEXPR_OR_CONST UIntType xor_mask = a;
``
]]
[[`BOOST_OVERRIDE`][
If `BOOST_NO_CXX11_OVERRIDE` is not defined (i.e. C++11 compliant compilers),
expands to `override` keyword, otherwise expands to nothing.
]]
[[`BOOST_STATIC_CONSTEXPR`][
This is a shortcut for `static BOOST_CONSTEXPR_OR_CONST`. For example, when defining const expr variables replace:
``
  static constexpr UIntType xor_mask = a;
``
with:
``
  BOOST_STATIC_CONSTEXPR UIntType xor_mask = a;
``
]]
[[`BOOST_DEFAULTED_FUNCTION(fun, body)`][
This macro is intended to be used within a class definition in order to declare a default implementation of function `fun`.
For the compilers that do not support C++11 defaulted functions the macro will expand into an inline function definition
with the `body` implementation. For example:
``
  struct my_struct
  {
      BOOST_DEFAULTED_FUNCTION(my_struct(), {})
  };
``
is equivalent to:
``
  struct my_struct
  {
      my_struct() = default;
  };
``
or:
``
  struct my_struct
  {
      my_struct() {}
  };
``
]]
[[`BOOST_DELETED_FUNCTION(fun)`][
This macro is intended to be used within a class definition in order to declare a deleted function `fun`.
For the compilers that do not support C++11 deleted functions the macro will expand into a private function
declaration with no definition. Since the macro may change the access mode, it is recommended to use this macro
at the end of the class definition. For example:
``
  struct noncopyable
  {
      BOOST_DELETED_FUNCTION(noncopyable(noncopyable const&))
      BOOST_DELETED_FUNCTION(noncopyable& operator= (noncopyable const&))
  };
``
is equivalent to:
``
  struct noncopyable
  {
      noncopyable(noncopyable const&) = delete;
      noncopyable& operator= (noncopyable const&) = delete;
  };
``
or:
``
  struct noncopyable
  {
  private:
      noncopyable(noncopyable const&);
      noncopyable& operator= (noncopyable const&);
  };
``
]]
[[
``
  BOOST_NOEXCEPT
  BOOST_NOEXCEPT_OR_NOTHROW
  BOOST_NOEXCEPT_IF(Predicate)
  BOOST_NOEXCEPT_EXPR(Expression)
``
][
If `BOOST_NO_CXX11_NOEXCEPT` is defined (i.e. C++03 compliant compilers) these macros are defined as:
[:
``
  #define BOOST_NOEXCEPT
  #define BOOST_NOEXCEPT_OR_NOTHROW throw()
  #define BOOST_NOEXCEPT_IF(Predicate)
  #define BOOST_NOEXCEPT_EXPR(Expression) false
``
]
If `BOOST_NO_CXX11_NOEXCEPT` is not defined (i.e. C++11 compliant compilers) they are defined as:
[:
``
  #define BOOST_NOEXCEPT noexcept
  #define BOOST_NOEXCEPT_OR_NOTHROW noexcept
  #define BOOST_NOEXCEPT_IF(Predicate) noexcept((Predicate))
  #define BOOST_NOEXCEPT_EXPR(Expression) noexcept((Expression))
``
]
]]
[[`BOOST_FINAL`][
If `BOOST_NO_CXX11_FINAL` is not defined (i.e. C++11 compliant compilers), expands to `final` keyword,
otherwise expands to nothing.
]]
[[`BOOST_MSVC_ENABLE_2012_NOV_CTP`][
For Microsoft Visual C++ 2012, enable the C++11 features supplied by the
November 2012 Community Technology Preview. These features are not automatically
enabled because the CTP is non-supported alpha code that is not recommended
for production use. This macro must be defined before including any Boost headers,
and must be defined for all translation units in the program, including Boost library builds.
This macro will no longer have any effect once an official Microsoft
release supports the CTP features.
]]
]

[endsect]

[section Macros that describe C++14 features not supported]

The following macros describe features in the 2014 ISO C++ standard, formerly known as C++0y,
that are not yet supported by a particular compiler or library.

[table
[[Macro ][Description ]]
[[`BOOST_NO_CXX14_AGGREGATE_NSDMI`][The compiler does not support member initializer for aggregates as in the following example:
[:
``
struct Foo
{
  int x, y = 42;
};

Foo foo = { 0 };
``
]
]]
[[`BOOST_NO_CXX14_BINARY_LITERALS`][The compiler does not binary literals (e.g. `0b1010`).]]
[[`BOOST_NO_CXX14_CONSTEXPR`][The compiler does not support relaxed `constexpr`.]]
[[`BOOST_NO_CXX14_DECLTYPE_AUTO`][The compiler does not support `decltype(auto)`.]]
[[`BOOST_NO_CXX14_DIGIT_SEPARATORS`][The compiler does not support digit separators (e.g. `1'000'000`).]]
[[`BOOST_NO_CXX14_STD_EXCHANGE`][The compiler does not support `std::exchange()`.]]
[[`BOOST_NO_CXX14_GENERIC_LAMBDAS`][The compiler does not support generic lambda (e.g. `[](auto v){ }`).]]
[[`BOOST_NO_CXX14_HDR_SHARED_MUTEX`][The standard library does not provide header <shared_mutex>.]]
[[`BOOST_NO_CXX14_INITIALIZED_LAMBDA_CAPTURES`][The compiler does not support initialized lambda capture (e.g. `[foo = 42]{ }`).]]
[[`BOOST_NO_CXX14_RETURN_TYPE_DEDUCTION`][The compiler does not support return type deduction for normal functions (e.g. `auto f() { return val; }`).]]
[[`BOOST_NO_CXX14_VARIABLE_TEMPLATES`][The compiler does not support variable template (e.g. `template <class T> T kibi = T(1024);`).]]
]

[endsect]

[#config_14_for_11]

[section Macros that allow use of C++14 features with C++11 or earlier compilers]

The following macros allow use of C++14 features even with compilers that do not yet
provide compliant C++14 support.

[table
[[Macro ][ Description ]]
[[`BOOST_CXX14_CONSTEXPR`][This macro works similar to `BOOST_CONSTEXPR`, but expands to `constexpr` only if the C++14 "relaxed" `constexpr` is available.]]
]

[endsect]

[section Macros that describe C++17 features not supported]

The following macros describe features in the 2017 ISO C++ standard, formerly known as C++1z,
that are not yet supported by a particular compiler or library.

[table
[[Macro ][Description ]]
[[`BOOST_NO_CXX17_HDR_OPTIONAL`][The compiler does not support the header `<optional>`.]]
[[`BOOST_NO_CXX17_HDR_VARIANT`][The compiler does not support the header `<variant>`.]]
[[`BOOST_NO_CXX17_HDR_STRING_VIEW`][The compiler does not support the header `<string_view>`.]]
[[`BOOST_NO_CXX17_STD_APPLY`][The compiler does not support `std::apply()`.]]
[[`BOOST_NO_CXX17_STD_INVOKE`][The compiler does not support `std::invoke()`.]]
[[`BOOST_NO_CXX17_ITERATOR_TRAITS`][The compiler does not support SFINAE-friendly `std::iterator_traits`.]]
[[`BOOST_NO_CXX17_IF_CONSTEXPR`][The compiler does not support `if constexpr`.]]
[[`BOOST_NO_CXX17_INLINE_VARIABLES`][The compiler does not support `inline` variables.]]
]

[endsect]

[#config_17_for_14]

[section Macros that allow use of C++17 features with C++14 or earlier compilers]

The following macros allow use of C++17 features even with compilers that do not yet
provide compliant C++17 support.

[table
[[Macro ][ Description ]]
[[`BOOST_INLINE_VARIABLE`][This macro expands to `inline` on compilers that support C++17 inline variables and to nothing otherwise. Users may need to check for `BOOST_NO_CXX17_INLINE_VARIABLES` for further adjustments to the code.]]
[[`BOOST_IF_CONSTEXPR`][Expands to `if constexpr` when supported, or `if` otherwise.]]
[[`BOOST_INLINE_CONSTEXPR`][This is a shortcut for `BOOST_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST`.]]
]

[endsect]

[section Macros that describe features that have been removed from the standard.]

The following macros describe features which were required by one version of the standard, but have been removed by later versions.

[table
[[Macro ][Description ]]
[[`BOOST_NO_CXX98_RANDOM_SHUFFLE`][The standard library no longer supports `std::random_shuffle()`. It was deprecated in C++11 and is removed from C++14.]]
[[`BOOST_NO_AUTO_PTR`][The standard library no longer supports `std::auto_ptr`. It was deprecated in C++11 and is removed from C++14.]]
[[`BOOST_NO_CXX98_FUNCTION_BASE`][The standard library no longer supports `std::unary_function` and `std::binary_function`. They were deprecated in C++11 and is removed from C++14.]]
[[`BOOST_NO_CXX98_BINDERS`][The standard library no longer supports `std::bind1st`, `std::bind2nd`, `std::ptr_fun` and `std::mem_fun`. They were deprecated in C++11 and is removed from C++14.]]
]

[endsect]

[#config_helpers]

[section Boost Helper Macros]

The following macros are either simple helpers, or macros that provide
workarounds for compiler/standard library defects.


[table
[[Macro           ][Description            ]]

[[`BOOST_WORKAROUND`][
This macro is used where a compiler specific workaround is required that is not otherwise
described by one of the other Boost.Config macros.  To use the macro you must first
``
#include <boost/config/workaround.hpp>
``
usage is then:
``
#if BOOST_WORKAROUND(MACRONAME, CONDITION)
   // workaround code goes here...
#else
   // Standard conforming code goes here...
#endif
``
where `MACRONAME` is a macro that usually describes the version number to be tested against, and `CONDITION`
is a comparison operator followed by a value.  For example `BOOST_WORKAROUND(BOOST_INTEL, <= 1010)` would 
evaluate to `1` for Intel C++ 10.1 and earlier.  

The macro can also be used with `BOOST_TESTED_AT` if all
current compiler versions exhibit the issue, but the issue is expected to be fixed at some later point.  

For example
`BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x590))` would normally evaluate to `1` for all values
of `__BORLANDC__` /unless/ the macro `BOOST_DETECT_OUTDATED_WORKAROUNDS` is defined, in which case evaluates to
`(__BORLANDC__ <= 0x590)`.

[*Note]: the ultimate source of documentation for this macro is in [@../../../../boost/config/workaround.hpp boost/config/workaround.hpp].
]]
[[`BOOST_PREVENT_MACRO_SUBSTITUTION`][
Sometimes you have a function name with the same name as a C macro, for example "min" and "max"
member functions, in which case one can prevent the function being expanded as a macro using:
``
someclass.min BOOST_PREVENT_MACRO_SUBSTITUTION(arg1, arg2);
``
The following also works in most, but not all, contexts:
``
(someclass.max)(arg1, arg2);
``
]]
[[`BOOST_DEDUCED_TYPENAME`][
Some compilers don't support the use of typename for dependent types in deduced
contexts. This macro expands to nothing on those compilers, and typename
elsewhere. For example, replace:
`template <class T> void f(T, typename T::type);`
with:
`template <class T> void f(T, BOOST_DEDUCED_TYPENAME T::type);`
]]
[[`BOOST_HASH_MAP_HEADER`][
The header to include to get the SGI `hash_map` class. This macro is only
available if `BOOST_HAS_HASH` is defined.
]]
[[`BOOST_HASH_SET_HEADER`][
The header to include to get the SGI `hash_set` class. This macro is only
available if `BOOST_HAS_HASH` is defined.
]]
[[`BOOST_SLIST_HEADER`][
The header to include to get the SGI `slist` class. This macro is only
available if `BOOST_HAS_SLIST` is defined.
]]
[[`BOOST_STD_EXTENSION_NAMESPACE`][
The namespace used for std library extensions (hashtable classes etc).
]]
[[`BOOST_STATIC_CONSTANT(Type, assignment)`][
On compilers which don't allow in-class initialization of static integral
constant members, we must use enums as a workaround if we want the constants
to be available at compile-time. This macro gives us a convenient way to
declare such constants.
For example instead of:
``
struct foo{
   static const int value = 2;
};
``
use:
``
struct foo{
   BOOST_STATIC_CONSTANT(int, value = 2);
};
``
]]
[[`BOOST_UNREACHABLE_RETURN(result)`][
Normally evaluates to nothing, but evaluates to return x; if the compiler
requires a return, even when it can never be reached.
]]
[[`BOOST_FALLTHROUGH`][ 
The BOOST_FALLTHROUGH macro can be used to annotate implicit fall-through 
between switch labels: 
`` 
 switch (x) { 
 case 40: 
 case 41: 
    if (truth_is_out_there) { 
       ++x; 
       BOOST_FALLTHROUGH;  // Use instead of/along with annotations in 
       // comments. 
    } else { 
      return x; 
    } 
    case 42: 
       ... 
`` 
As shown in the example above, the BOOST_FALLTHROUGH macro should be 
followed by a semicolon. It is designed to mimic control-flow statements 
like 'break;', so it can be placed in most places where 'break;' can, but 
only if there are no statements on the execution path between it and the 
next switch label. 

When compiled with Clang >3.2 in C++11 mode, the BOOST_FALLTHROUGH macro is 
expanded to `[[clang::fallthrough]]` attribute, which is analysed when 
performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough'). 
See clang [@http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough 
documentation on language extensions for details.] 

When used with unsupported compilers, the BOOST_FALLTHROUGH macro has no 
effect on diagnostics. 

In either case this macro has no effect on runtime behavior and performance 
of code. 
]] 
[[`BOOST_EXPLICIT_TEMPLATE_TYPE(t)`

  `BOOST_EXPLICIT_TEMPLATE_NON_TYPE(t,v)`

  `BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE(t)`

  `BOOST_APPEND_EXPLICIT_TEMPLATE_NON_TYPE(t,v)`][
Some compilers silently "fold" different function template instantiations if
some of the template parameters don't appear in the function parameter list.
For instance:
``
  #include <iostream>
  #include <ostream>
  #include <typeinfo>

  template <int n>
  void f() { std::cout << n << ' '; }

  template <typename T>
  void g() { std::cout << typeid(T).name() << ' '; }

  int main() {
    f<1>();
    f<2>();

    g<int>();
    g<double>();
  }
``
incorrectly outputs [^2 2 double double] on VC++ 6. These macros, to be used
in the function parameter list, fix the problem without effects on the calling
syntax. For instance, in the case above write:
``
  template <int n>
  void f(BOOST_EXPLICIT_TEMPLATE_NON_TYPE(int, n)) { ... }

  template <typename T>
  void g(BOOST_EXPLICIT_TEMPLATE_TYPE(T)) { ... }
``
Beware that they can declare (for affected compilers) a dummy defaulted
parameter, so they

[*a)] should be always invoked [*at the end] of the parameter list

[*b)] can't be used if your function template is multiply declared.

Furthermore, in order to add any needed comma separator, an `APPEND_*` version
must be used when the macro invocation appears after a normal parameter
declaration or after the invocation of another macro of this same group.
]]
[[`BOOST_USE_FACET(Type, loc)`][
When the standard library does not have a conforming `std::use_facet` there
are various workarounds available, but they differ from library to library.
This macro provides a consistent way to access a locale's facets. For example,
replace:
`std::use_facet<Type>(loc);`
with:
`BOOST_USE_FACET(Type, loc);`
Note do not add a `std::` prefix to the front of `BOOST_USE_FACET`.
]]
[[`BOOST_HAS_FACET(Type, loc)`][
When the standard library does not have a comforming `std::has_facet` there
are various workarounds available, but they differ from library to library.
This macro provides a consistent way to check a locale's facets. For example,
replace:
`std::has_facet<Type>(loc);`
with:
`BOOST_HAS_FACET(Type, loc);`
Note do not add a `std::` prefix to the front of `BOOST_HAS_FACET`.
]]
[[`BOOST_NESTED_TEMPLATE`][
Member templates are supported by some compilers even though they can't use
the `A::template member<U>` syntax, as a workaround replace:
`typedef typename A::template rebind<U> binder;`
with:
`typedef typename A::BOOST_NESTED_TEMPLATE rebind<U> binder;`
]]
[[`BOOST_STRINGIZE(X)`][
Converts the parameter `X` to a string after macro replacement on `X` has
been performed.
]]
[[`BOOST_JOIN(X,Y)`][
This piece of macro magic joins the two arguments together, even when one of
the arguments is itself a macro (see 16.3.1 in C++ standard). This is normally
used to create a mangled name in combination with a predefined macro such a
\_\_LINE__.
]]
[[`BOOST_RESTRICT`][
This macro can be used in place of the compiler specific variant of the C99 `restrict` keyword to
notify the compiler that, for the lifetime of the qualified pointer variable, only it and its
derivative value will be used to gain access to the object it references. This limits the effect of
pointer aliasing and helps the optimizers in generating better code. However, i this condition is
violated, undefined behavior may occurs.

Usage example:
``
  void perform_computation( float* BOOST_RESTRICT in, float* BOOST_RESTRICT out )
  {
    *out = *in * 0.5f;
  }
``
]]
[[`BOOST_FORCEINLINE`][
This macro can be used in place of the `inline` keyword to instruct the compiler
that the function should always be inlined.
Overuse of this macro can lead to significant bloat, while good use can increase
performance in certain cases, such as computation-intensive code built through
generative programming techniques.

Usage example:
``
  template<class T>
  BOOST_FORCEINLINE T& f(T& t)
  {
      return t;
  }
``

Note that use of this macro can lead to cryptic error messages with some compilers.
Consider defining it to `inline` before including the Boost.Config header in order to be
able to debug errors more easily.
]]
[[`BOOST_NOINLINE`][
This macro can be used in place of the `inline` keyword to instruct the compiler
that the function should never be inlined. One should typically use this macro
to mark functions that are unlikely to be called, such as error handling routines.

Usage example:
``
  BOOST_NOINLINE void handle_error(const char* descr)
  {
      // ...
  }
``
]]
[[`BOOST_NORETURN`][
This macro can be used before the function declaration or definition to instruct the compiler
that the function does not return normally (i.e. with a `return` statement or by leaving
the function scope, if the function return type is `void`). The macro can be used to mark
functions that always throw exceptions or terminate the application. Compilers that support
this markup may use this information to specifically organize the code surrounding calls to
this function and suppress warnings about missing `return` statements in the functions
enclosing such calls.

Usage example:
``
  BOOST_NORETURN void on_error_occurred(const char* descr)
  {
      throw std::runtime_error(descr);
  }
``

If the compiler does not support this markup, `BOOST_NORETURN` is defined empty and an
additional macro `BOOST_NO_NORETURN` is defined.
]]
[[`BOOST_LIKELY(X)`

  `BOOST_UNLIKELY(X)`][
These macros communicate to the compiler that the conditional expression `X` is likely
or unlikely to yield a positive result. The expression should result in a boolean value.
The result of the macro is an integer or boolean value equivalent to the result of `X`.

The macros are intended to be used in branching statements. The additional hint they provide
can be used by the compiler to arrange the compiled code of the branches more effectively.

Usage example:
``
  if (BOOST_UNLIKELY(ptr == NULL))
    handle_error("ptr is NULL");
``
]]
[[`BOOST_ATTRIBUTE_UNUSED`][Expands to `__attribute__((unused))` when this is available - 
can be used to disable compiler warnings relating to unused types or variables.]]
[[`BOOST_ATTRIBUTE_NODISCARD`][Expands to `[[nodiscard]]` when this is available - 
can be used to create a warning when a type or variable is unused.]]
[[`BOOST_ATTRIBUTE_NO_UNIQUE_ADDRESS`][Expands to `[[no_unique_address]]` when this is available - 
can be used to indicate that a non-static data member need not have a unique address (for example empty classes).]]
[[`BOOST_MAY_ALIAS`, `BOOST_NO_MAY_ALIAS`][
`BOOST_MAY_ALIAS` expands to a type attribute that can be used to mark types that may
alias other types. Pointers or references to such marked types can be used to access objects
of other types. If the compiler supports this feature `BOOST_NO_MAY_ALIAS` is not defined.
Otherwise `BOOST_MAY_ALIAS` expands to nothing and `BOOST_NO_MAY_ALIAS` is defined.

Usage example:
``
  struct BOOST_MAY_ALIAS aliasing_struct;
  typedef unsigned int BOOST_MAY_ALIAS aliasing_uint;
``
]]
[[`BOOST_PRAGMA_MESSAGE(M)`][Defined in header `<boost/config/pragma_message.hpp>`,
this macro expands to the equivalent of `#pragma message(M)`. `M` must be a string
literal.

Example: `BOOST_PRAGMA_MESSAGE("This header is deprecated.")`

The messages issued by `BOOST_PRAGMA_MESSAGE` can be suppressed by defining the macro
`BOOST_DISABLE_PRAGMA_MESSAGE`.]]

[[`BOOST_HEADER_DEPRECATED(A)`][Defined in header `<boost/config/header_deprecated.hpp>`,
this macro issues the message "This header is deprecated. Use `A` instead." via
`BOOST_PRAGMA_MESSAGE`. `A` must be a string literal.

Example: `BOOST_HEADER_DEPRECATED("<boost/config/workaround.hpp>")`

The messages issued by `BOOST_HEADER_DEPRECATED` can be suppressed by defining the macro
`BOOST_ALLOW_DEPRECATED_HEADERS`.]]
]

[endsect]

[#config_info_macros]

[section Boost Informational Macros]

The following macros describe boost features; these are, generally speaking
the only boost macros that should be tested in user code.

[table

[[Macro            ][Header         ][Description               ]]

[[`BOOST_VERSION`][`<boost/version.hpp>`][
Describes the boost version number in XYYYZZ format such that:
`(BOOST_VERSION % 100)` is the sub-minor version, `((BOOST_VERSION / 100) % 1000)`
is the minor version, and `(BOOST_VERSION / 100000)` is the major version.
]]
[[`BOOST_NO_INT64_T`][`<boost/cstdint.hpp>` `<boost/stdint.h>`][
Defined if there are no 64-bit integral types: `int64_t`, `uint64_t` etc.
]]
[[`BOOST_NO_INTEGRAL_INT64_T`][`<boost/cstdint.hpp>` `<boost/stdint.h>`][
Defined if `int64_t` as defined by `<boost/cstdint.hpp>` is not usable in
integral constant expressions.
]]
[[`BOOST_MSVC`][`<boost/config.hpp>`][
Defined if the compiler is really Microsoft Visual C++, as opposed to one
of the many other compilers that also define `_MSC_VER`.  Has the same value as 
_MSC_VER.
]]
[[`BOOST_MSVC_FULL_VER`][`<boost/config.hpp>`][
Defined to a normalised 9 digit version of _MSC_FULL_VER (which sometimes only has 8 digits), 
the macro has the form VVMMPPPPP where VV is the major version number, MM is the minor version number, and
PPPPP is the compiler build number.
]]
[[`BOOST_GCC`][`<boost/config.hpp>`][
Defined if the compiler is really GCC, as opposed to one
of the many other compilers that also define `__GNUC__`.  Has the value:
`__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__`.
]]
[[`BOOST_INTEL`][`<boost/config.hpp>`][
Defined if the compiler is an Intel compiler, takes the same value as the
compiler version macro.
]]
[[`BOOST_CLANG`][`<boost/config.hpp>`][
Defined to 1 if the compiler is the Clang compiler.
]]
[[`BOOST_BORLANDC`][`<boost/config.hpp>`][
Defined to the value of __BORLANDC__ if the compiler is the Embarcadero
non-clang based compiler.
]]
[[`BOOST_CODEGEARC`][`<boost/config.hpp>`][
Defined to the value of __CODEGEARC__ if the compiler is the Embarcadero
non-clang based compiler.
]]
[[`BOOST_EMBTC`][`<boost/config.hpp>`][
Defined to the value of __CODEGEARC__ if the compiler is the Embarcadero
clang based compiler.
]]
[[`BOOST_WINDOWS`][`<boost/config.hpp>`][
Defined if the Windows platform API is available.
]]
[[`BOOST_DINKUMWARE_STDLIB`][`<boost/config.hpp>`][
Defined if the dinkumware standard library is in use, takes the same value
as the Dinkumware library version macro `_CPPLIB_VER` if defined, otherwise 1.
]]
[[`BOOST_NO_WREGEX`][`<boost/regex.hpp>`][
Defined if the regex library does not support wide character regular
expressions.
]]
[[`BOOST_COMPILER`][`<boost/config.hpp>`][
Defined as a string describing the name and version number of the compiler
in use. Mainly for debugging the configuration.
]]
[[`BOOST_STDLIB`][`<boost/config.hpp>`][
Defined as a string describing the name and version number of the standard
library in use. Mainly for debugging the configuration.
]]
[[`BOOST_PLATFORM`][`<boost/config.hpp>`][
Defined as a string describing the name of the platform. Mainly for debugging
the configuration.
]]
[[`BOOST_LIBSTDCXX_VERSION`][`<boost/config.hpp>`][
Defined if the libstdc++ standard library is in use.
Has the value of normalised 5 digit integer of the form VVMMM where
VV is the major version number, MM is the minor version number.
]]
]

[endsect]

[#deprecated_macros]

[section Boost Deprecated Macros]

The following have been deprecated; please use the replacements instead.
They will be removed in a future version of boost.

[table

[[Deprecated Macro][Replacement][When deprecated][When removed]]

[[`BOOST_NO_0X_HDR_ARRAY`][`BOOST_NO_CXX11_HDR_ARRAY`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_CHRONO`][`BOOST_NO_CXX11_HDR_CHRONO`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_CODECVT`][`BOOST_NO_CXX11_HDR_CODECVT`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_CONDITION_VARIABLE`][`BOOST_NO_CXX11_HDR_CONDITION_VARIABLE`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_FORWARD_LIST`][`BOOST_NO_CXX11_HDR_FORWARD_LIST`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_FUTURE`][`BOOST_NO_CXX11_HDR_FUTURE`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_INITIALIZER_LIST`][`BOOST_NO_CXX11_HDR_INITIALIZER_LIST`][Boost 1.50][]]
[[`BOOST_NO_INITIALIZER_LISTS`][`BOOST_NO_CXX11_HDR_INITIALIZER_LIST`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_MUTEX`][`BOOST_NO_CXX11_HDR_MUTEX`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_RANDOM`][`BOOST_NO_CXX11_HDR_RANDOM`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_RATIO`][`BOOST_NO_CXX11_HDR_RATIO`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_REGEX`][`BOOST_NO_CXX11_HDR_REGEX`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_SYSTEM_ERROR`][`BOOST_NO_CXX11_HDR_SYSTEM_ERROR`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_THREAD`][`BOOST_NO_CXX11_HDR_THREAD`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_TUPLE`][`BOOST_NO_CXX11_HDR_TUPLE`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_TYPE_TRAITS`][`BOOST_NO_CXX11_HDR_TYPE_TRAITS`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_TYPEINDEX`][`BOOST_NO_CXX11_HDR_TYPEINDEX`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_UNORDERED_SET`][`BOOST_NO_CXX11_HDR_UNORDERED_SET`][Boost 1.50][]]
[[`BOOST_NO_0X_HDR_UNORDERED_MAP`][`BOOST_NO_CXX11_HDR_UNORDERED_MAP`][Boost 1.50][]]
[[`BOOST_NO_STD_UNORDERED`][`BOOST_NO_CXX11_HDR_UNORDERED_SET`][Boost 1.50][]]
[[][][][]]
[[`BOOST_NO_AUTO_DECLARATIONS`][`BOOST_NO_CXX11_AUTO_DECLARATIONS`][Boost 1.51][]]
[[`BOOST_NO_AUTO_MULTIDECLARATIONS`][`BOOST_NO_CXX11_AUTO_MULTIDECLARATIONS`][Boost 1.51][]]
[[`BOOST_NO_CHAR16_T`][`BOOST_NO_CXX11_CHAR16_T`][Boost 1.51][]]
[[`BOOST_NO_CHAR32_T`][`BOOST_NO_CXX11_CHAR32_T`][Boost 1.51][]]
[[`BOOST_NO_TEMPLATE_ALIASES`][`BOOST_NO_CXX11_TEMPLATE_ALIASES`][Boost 1.51][]]
[[`BOOST_NO_CONSTEXPR`][`BOOST_NO_CXX11_CONSTEXPR`][Boost 1.51][]]
[[`BOOST_NO_DECLTYPE`][`BOOST_NO_CXX11_DECLTYPE`][Boost 1.51][]]
[[`BOOST_NO_DECLTYPE_N3276`][`BOOST_NO_CXX11_DECLTYPE_N3276`][Boost 1.51][]]
[[`BOOST_NO_DEFAULTED_FUNCTIONS`][`BOOST_NO_CXX11_DEFAULTED_FUNCTIONS`][Boost 1.51][]]
[[`BOOST_NO_DELETED_FUNCTIONS`][`BOOST_NO_CXX11_DELETED_FUNCTIONS`][Boost 1.51][]]
[[`BOOST_NO_EXPLICIT_CONVERSION_OPERATORS`][`BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS`][Boost 1.51][]]
[[`BOOST_NO_EXTERN_TEMPLATE`][`BOOST_NO_CXX11_EXTERN_TEMPLATE`][Boost 1.51][]]
[[`BOOST_NO_FUNCTION_TEMPLATE_DEFAULT_ARGS`][`BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS`][Boost 1.51][]]
[[`BOOST_NO_LAMBDAS`][`BOOST_NO_CXX11_LAMBDAS`][Boost 1.51][]]
[[`BOOST_NO_LOCAL_CLASS_TEMPLATE_PARAMETERS`][`BOOST_NO_CXX11_LOCAL_CLASS_TEMPLATE_PARAMETERS`][Boost 1.51][]]
[[`BOOST_NO_NOEXCEPT`][`BOOST_NO_CXX11_NOEXCEPT`][Boost 1.51][]]
[[`BOOST_NO_NULLPTR`][`BOOST_NO_CXX11_NULLPTR`][Boost 1.51][]]
[[`BOOST_NO_RAW_LITERALS`][`BOOST_NO_CXX11_RAW_LITERALS`][Boost 1.51][]]
[[`BOOST_NO_RVALUE_REFERENCES`][`BOOST_NO_CXX11_RVALUE_REFERENCES`][Boost 1.51][]]
[[`BOOST_NO_SCOPED_ENUMS`][`BOOST_NO_CXX11_SCOPED_ENUMS`][Boost 1.51][]]
[[`BOOST_NO_STATIC_ASSERT`][`BOOST_NO_CXX11_STATIC_ASSERT`][Boost 1.51][]]
[[`BOOST_NO_STD_UNORDERED`][`BOOST_NO_CXX11_STD_UNORDERED`][Boost 1.51][]]
[[`BOOST_NO_UNICODE_LITERALS`][`BOOST_NO_CXX11_UNICODE_LITERALS`][Boost 1.51][]]
[[`BOOST_NO_UNIFIED_INITIALIZATION_SYNTAX`][`BOOST_NO_CXX11_UNIFIED_INITIALIZATION_SYNTAX`][Boost 1.51][]]
[[`BOOST_NO_VARIADIC_TEMPLATES`][`BOOST_NO_CXX11_VARIADIC_TEMPLATES`][Boost 1.51][]]
[[`BOOST_NO_VARIADIC_MACROS`][`BOOST_NO_CXX11_VARIADIC_MACROS`][Boost 1.51][]]
[[`BOOST_NO_NUMERIC_LIMITS_LOWEST`][`BOOST_NO_CXX11_NUMERIC_LIMITS`][Boost 1.51][]]
[[][][][]]
[[`BOOST_HAS_STATIC_ASSERT`][`BOOST_NO_CXX11_STATIC_ASSERT` (negated)][Boost 1.53][]]
[[`BOOST_HAS_VARIADIC_TMPL`][`BOOST_NO_CXX11_VARIADIC_TEMPLATES` (negated)][Boost 1.53][]]
[[`BOOST_HAS_RVALUE_REFS`][`BOOST_NO_CXX11_RVALUE_REFERENCES` (negated)][Boost 1.53][]]
[[`BOOST_HAS_CHAR16_T`][`BOOST_NO_CXX11_CHAR16_T` (negated)][Boost 1.53][]]
[[`BOOST_HAS_CHAR32_T`][`BOOST_NO_CXX11_CHAR32_T` (negated)][Boost 1.53][]]
]

[endsect]

[section Macros for libraries with separate source code]

The following macros and helper headers are of use to authors whose libraries
include separate source code, and are intended to address several issues:

* Controlling shared library symbol visibility
* Fixing the ABI of the compiled library
* Selecting which compiled library to link against based upon the compilers settings

See [@http://www.boost.org/development/separate_compilation.html Guidelines for Authors of Boost Libraries Containing Separate Source]

[section Macros controlling shared library symbol visibility]

Some compilers support C++ extensions that control which symbols 
will be exported from shared libraries such as dynamic shared objects (DSO's) on Unix-like
systems or dynamic-link libraries (DLL's) on Windows.

The Microsoft VC++ compiler has long supplied 
`__declspec(dllexport)` and `__declspec(dllimport)` extensions for this purpose,
as do virtually all other compilers targeting the Windows platform.
 
Modern versions of the GNU GCC compiler provide the `__attribute__((visibility("default")))` 
extension to indicate that a symbol should be exported. All other symbols may be hidden by using the
`-fvisibility-hidden` or `-fvisibility-ms-compat` compiler switches.

Boost supplies several macros to make it easier to manage symbol visibility in a way that
is portable between compilers and operating systems.

[table
[[Macro       ][Description       ]]
[[`BOOST_SYMBOL_EXPORT`][
Defines the syntax of a C++ language extension that indicates a symbol is to be exported from a shared library.
If the compiler has no such extension, the macro is defined with no replacement text. 
]]
[[`BOOST_SYMBOL_IMPORT`][
Defines the syntax of a C++ language extension that indicates a symbol is to be imported from a shared library.
If the compiler has no such extension, the macro is defined with no replacement text. 
]]
[[`BOOST_SYMBOL_VISIBLE`][
Defines the syntax of a C++ language extension that indicates a symbol is to be globally visible.
If the compiler has no such extension, the macro is defined with no replacement text. 
Needed for classes that are not otherwise exported, but are used by RTTI. Examples include
class for objects that will be thrown as exceptions or used in dynamic_casts,
across shared library boundaries. For example, a header-only exception class might look like this:
``
  class BOOST_SYMBOL_VISIBLE my_exception : public std::runtime_error { ... };
`` 
Without BOOST_SYMBOL_VISIBLE, it would be impossible to catch my_exception thrown from a shared library
compiled by GCC with the -fvisibility=hidden option.
]]
[[`BOOST_HAS_DECLSPEC`][
The compiler has C++ extensions `__declspec(dllexport)` and `__declspec(dllimport)` to control
export/import of symbols from shared libraries.
['Deprecated. This macro is no longer necessary since BOOST_SYMBOL_EXPORT and BOOST_SYMBOL_IMPORT
are now supplied. It is provided to support legacy code.]
]]
]

Typical usage:

[*boost/foo/config.hpp]

    ...
    #if defined(BOOST_ALL_DYN_LINK) || defined(BOOST_FOO_DYN_LINK)
    # if defined(BOOST_FOO_SOURCE)
    #   define BOOST_FOO_DECL BOOST_SYMBOL_EXPORT
    # else 
    #   define BOOST_FOO_DECL BOOST_SYMBOL_IMPORT
    # endif
    #else
    # define BOOST_FOO_DECL
    #endif
    ...
 
[*boost/foo/foo.hpp] 
  
    #include <boost/foo/config.hpp>
    ...
    class BOOST_FOO_DECL bar { ... };
    ...
    void BOOST_FOO_DECL f();
    ...

[*boost/libs/foo/src/foo.cpp] 
   
    #define BOOST_FOO_SOURCE
    #include <boost/foo/foo.hpp>    
    ...
    void BOOST_FOO_DECL f()
    {
      ...
    }
    ...
     
[endsect]

[section ABI Fixing]

When linking against a pre-compiled library it vital that the ABI used by the
compiler when building the library ['matches exactly] the ABI used by the code
using the library.  In this case ABI means things like the struct packing
arrangement used, the name mangling scheme used, or the size of some types
(enum types for example).  This is separate from things like threading support,
or runtime library variations, which have to be dealt with by build variants.
To put this in perspective there is one compiler (Borland's) that has so many
compiler options that make subtle changes to the ABI, that at least in theory
there 3200 combinations, and that's without considering runtime library
variations. Fortunately these variations can be managed by `#pragma`'s that
tell the compiler what ABI to use for the types declared in your library.
In order to avoid sprinkling `#pragma`'s all over the boost headers, there are
some prefix and suffix headers that do the job. Typical usage is:

[*my_library.hpp]

    #ifndef MY_INCLUDE_GUARD
    #define MY_INCLUDE_GUARD

    // all includes go here:
    ``[^[*#include <boost/config.hpp>]]``
    #include <whatever>

    ``[^[*#include <boost/config/abi_prefix.hpp>]]`` // must be the last #include

    namespace boost {

    // your code goes here

    }

    ``[^[*#include <boost/config/abi_suffix.hpp>]]`` // pops abi_prefix.hpp pragmas

    #endif // include guard

[*my_library.cpp]

    ...
    // nothing special need be done in the implementation file
    ...

The user can disable this mechanism by defining `BOOST_DISABLE_ABI_HEADERS`, or
they can define `BOOST_ABI_PREFIX` and/or `BOOST_ABI_SUFFIX` to point to their
own prefix/suffix headers if they so wish.

[endsect]

[section Automatic library selection]

It is essential that users link to a build of a library which was built against
the same runtime library that their application will be built against -if this
does not happen then the library will not be binary compatible with their own
code- and there is a high likelihood  that their application will experience
runtime crashes.  These kinds of problems can be extremely time consuming and
difficult to debug, and often lead to frustrated users and authors alike (simply
selecting the right library to link against is not as easy as it seems when
their are 6-8 of them to chose from, and some users seem to be blissfully
unaware that there even are different runtimes available to them).

To solve this issue, some compilers allow source code to contain `#pragma`'s that
instruct the linker which library to link against, all the user need do is
include the headers they need, place the compiled libraries in their library
search path, and the compiler and linker do the rest. Boost.config supports
this via the header `<boost/config/auto_link.hpp>`, before including this header
one or more of the following macros need to be defined:

[variablelist
[[`BOOST_LIB_NAME`][
Required: An identifier containing the basename of the library, for
example 'boost_regex'.
]]
[[`BOOST_DYN_LINK`][
Optional: when set link to dll rather than static library.
]]
[[`BOOST_LIB_DIAGNOSTIC`][
Optional: when set the header will print out the name of the library selected
(useful for debugging).
]]
[[`BOOST_AUTO_LINK_NOMANGLE`][
Optional: whan set specifies that we should link to BOOST_LIB_NAME.lib, rather than a mangled-name version.]]
[[`BOOST_AUTO_LINK_TAGGED`][Optional: Specifies that we link to libraries built with the --layout=tagged option.
                          This is essentially the same as the default name-mangled version, but without
                          the compiler name and version, or the Boost version.  Just the build options.]]
[[`BOOST_AUTO_LINK_SYSTEM`][Optional: Specifies that we link to libraries built with the --layout=system option.
                          This is essentially the same as the non-name-mangled version, but with
                          the prefix to differentiate static and dll builds]]
]

If the compiler supports this mechanism, then it will be told to link against
the appropriately named library, the actual algorithm used to mangle the name
of the library is documented inside `<boost/config/auto_link.hpp>` and has to
match that used to create the libraries via bjam 's install rules.


[*my_library.hpp]

    ...
    //
    // Don't include auto-linking code if the user has disabled it by
    // defining BOOST_ALL_NO_LIB, or BOOST_MY_LIBRARY_NO_LIB, or if this 
    // is one of our own source files (signified by BOOST_MY_LIBRARY_SOURCE):
    //
    #if !defined(BOOST_ALL_NO_LIB) && !defined(BOOST_MY_LIBRARY_NO_LIB) && !defined(BOOST_MY_LIBRARY_SOURCE)
    #  define BOOST_LIB_NAME boost_my_library
    #  ifdef BOOST_MY_LIBRARY_DYN_LINK
    #     define BOOST_DYN_LINK
    #  endif
    #  include <boost/config/auto_link.hpp>
    #endif
    ...

[*my_library.cpp]

    // define BOOST_MY_LIBRARY_SOURCE so that the header knows that the
    // library is being built (possibly exporting rather than importing code)
    //
    #define BOOST_MY_LIBRARY_SOURCE

    #include <boost/my_library/my_library.hpp>
    ...

[endsect]

[endsect]

[endsect]



