Boost C++ Libraries

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Boost Macro Reference

Broad C++ Standard Level Checks
Macros that describe C++03 defects
Macros that describe optional features
Macros that describe C++11 features not supported
Macros that allow use of C++11 features with C++03 compilers
Macros that describe C++14 features not supported
Macros that allow use of C++14 features with C++11 or earlier compilers
Macros that describe C++17 features not supported
Macros that allow use of C++17 features with C++14 or earlier compilers
Macros that describe C++20 features not supported
Macros that describe C++23 features not supported
Macros that describe features that have been removed from the standard.
Boost Helper Macros
Boost Informational Macros
Boost Deprecated Macros
Macros for libraries with separate source code

These are for the times when you just want to check "does this compiler conform to C++11" or some such.

C++ Standard Level

The macro BOOST_CXX_VERSION is set to the C++ standard version - it has the same value as __cplusplus if __cplusplus is set to a sensible value, otherwise the current C++ standard level in effect (for example for MSVC this is set to the value of _MSVC_LANG).

Available standard values are:

standard

value

2003

199711L

2011

201103L

2014

201402L

2017

201703L

2020

202002L

You should use this macro as a basic sanity check that the compiler is minimally at the required standard level - there may still be bugs, unimplemented features, and/or missing headers. The individual feature checks should be used for those.

Strict Standard Level Checks

The following macros:

BOOST_NO_CXX03
BOOST_NO_CXX11
BOOST_NO_CXX14
BOOST_NO_CXX17

Are set if any of our defect macros are set for that standard level, .

Note that these are therefore very strict checks and as a result, other than very recent gcc/clang releases, many compilers will end up defining all of these macros: even when BOOST_CXX_VERSION indicates a much more recent standard is in effect.

Strict Standard Check Headers

The following headers:

#include <boost/config/assert_cxx03.hpp>
#include <boost/config/assert_cxx11.hpp>
#include <boost/config/assert_cxx14.hpp>
#include <boost/config/assert_cxx17.hpp>

Can be used to assert that none of our defect macros are set for that standard (or any older standards).

The headers will provide a slightly more useful error message than just checking on BOOST_NO_CXX03 for example, as they will indicate which defect macro produced the error.

As noted abovem these are very strict checks, and therefore other than recent gcc/clang releases, many compilers will genrate a #error on including any of these headers.

SD6 Feature Test Macros

Note that none of the above checks take into account any standard library SD6 feature test macros, as doing so would require #includeing almost the whole standard library.

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.

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 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> 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> 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> 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(); }

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

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_MAP_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> 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).

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.

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_ALIGNOF

The compiler does not support the alignof 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 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>. Note that this header is deprecated post C++17, and therefore the macro may be set as a result of the feature being deliberately removed.

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 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 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 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 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.

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

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.

BOOST_NULLPTR

If BOOST_NO_CXX11_NULLPTR is not defined (i.e. C++11 compliant compilers), expands to nullptr, otherwise expands to 0.

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.

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);).

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

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.

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.

Macro

Description

BOOST_NO_CXX17_HDR_ANY

The compiler does not support the header <any>.

BOOST_NO_CXX17_HDR_CHARCONV

The compiler does not support the header <charconv>.

BOOST_NO_CXX17_HDR_EXECUTION

The compiler does not support the header <execution>.

BOOST_NO_CXX17_HDR_FILESYSTEM

The compiler does not support the header <filesystem>.

BOOST_NO_CXX17_HDR_MEMORY_RESOURCE

The compiler does not support the header <memory_resource>.

BOOST_NO_CXX17_HDR_OPTIONAL

The compiler does not support the header <optional>.

BOOST_NO_CXX17_HDR_STRING_VIEW

The compiler does not support the header <string_view>.

BOOST_NO_CXX17_HDR_VARIANT

The compiler does not support the header <variant>.

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.

BOOST_NO_CXX17_DEDUCTION_GUIDES

The compiler does not support class template argument deduction (CTAD) guides.

BOOST_NO_CXX17_AUTO_NONTYPE_TEMPLATE_PARAMS

The compiler does not support auto non-type template parameters.

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

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.

The following macros describe features in the 2020 ISO C++ standard, formerly known as C++2a, that are not yet supported by a particular compiler or library.

Macro

Description

BOOST_NO_CXX20_HDR_BARRIER

The compiler does not support the header <barrier>.

BOOST_NO_CXX20_HDR_FORMAT

The compiler does not support the header <format>.

BOOST_NO_CXX20_HDR_SOURCE_LOCATION

The compiler does not support the header <source_location>.

BOOST_NO_CXX20_HDR_BIT

The compiler does not support the header <bit>.

BOOST_NO_CXX20_HDR_LATCH

The compiler does not support the header <latch>.

BOOST_NO_CXX20_HDR_SPAN

The compiler does not support the header <span>.

BOOST_NO_CXX20_HDR_COMPARE

The compiler does not support the header <compare>.

BOOST_NO_CXX20_HDR_NUMBERS

The compiler does not support the header <numbers>.

BOOST_NO_CXX20_HDR_STOP_TOKEN

The compiler does not support the header <stop_token>.

BOOST_NO_CXX20_HDR_CONCEPTS

The compiler does not support the header <concepts>.

BOOST_NO_CXX20_HDR_RANGES

The compiler does not support the header <ranges>.

BOOST_NO_CXX20_HDR_SYNCSTREAM

The compiler does not support the header <syncstream>.

BOOST_NO_CXX20_HDR_COROUTINE

The compiler does not support the header <coroutine>.

BOOST_NO_CXX20_HDR_SEMAPHORE

The compiler does not support the header <semaphore>.

BOOST_NO_CXX20_HDR_VERSION

The compiler does not support the header <version>.

The following macros describe features in the 2023 ISO C++ standard, formerly known as C++2b, that are not yet supported by a particular compiler or library.

Macro

Description

BOOST_NO_CXX23_HDR_EXPECTED

The compiler does not support the header <expected>.

BOOST_NO_CXX23_HDR_FLAT_MAP

The compiler does not support the header <flat_map>.

BOOST_NO_CXX23_HDR_FLAT_SET

The compiler does not support the header <flat_set>.

BOOST_NO_CXX23_HDR_GENERATOR

The compiler does not support the header <generator>.

BOOST_NO_CXX23_HDR_MDSPAN

The compiler does not support the header <mdspan>.

BOOST_NO_CXX23_HDR_PRINT

The compiler does not support the header <print>.

BOOST_NO_CXX23_HDR_SPANSTREAM

The compiler does not support the header <spanstream>.

BOOST_NO_CXX23_HDR_STACKTRACE

The compiler does not support the header <stacktrace>.

BOOST_NO_CXX23_HDR_STDFLOAT

The compiler does not support the header <stdfloat>.

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

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.

BOOST_NO_CXX11_ATOMIC_SMART_PTR

The standard library no longer supports atomic overloads for std::shared_ptr: use std::atomic<shared_ptr<T>> instead.

BOOST_NO_CXX11_HDR_CODECVT

The standard library no longer supports <codecvt>, there is as yet no replacement.

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

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_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 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 values will be used to access the object it references. This limits the effect of pointer aliasing and helps optimizers in generating better code. However, if this condition is violated, undefined behavior may occur.

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_DEPRECATED(M)

Expands to an attribute for a symbol that generates warnings when that symbol is used in code. The warnings may contain a message M, which must be a string literal. This attribute may be applied to types, functions or objects and is typically used to mark parts of the API as deprecated with a recommendation of replacement.

Example:

BOOST_DEPRECATED("Use bar() instead.")
void foo();

template< typename T >
class BOOST_DEPRECATED("Use std::unique_ptr instead.") auto_ptr
{
};

BOOST_DEPRECATED("Use std::numeric_limits<int>::max() instead.")
const int max_int = 0x7fffffff;

The warnings issued by BOOST_DEPRECATED can be suppressed by defining BOOST_ALLOW_DEPRECATED_SYMBOLS or BOOST_ALLOW_DEPRECATED macros.

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 BOOST_ALLOW_DEPRECATED_HEADERS or BOOST_ALLOW_DEPRECATED macros.

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

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_CLANG_VERSION

<boost/config.hpp>

Defined to the version of the Clang compiler, usually __clang_major__ * 10000 + __clang_minor__ * 100 + __clang_patchlevel__. On Apple Clang, has a best-effort value reflecting the upstream version, rather than the Apple version.

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_MSSTL_VERSION

<boost/config.hpp>

Defined if the Microsoft Visual C++ standard library is in use. Has the value of _MSVC_STL_VERSION when that is defined, and a synthesized value of the same format otherwise. Example values are 143 for VS2022/msvc-14.3, 142 for VS2019/msvc-14.2, 141 for VS2017/msvc-14.1, 140 for VS2015/msvc-14.0, 120 for VS2013/msvc-12.0, and so on.

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.

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

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

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 Guidelines for Authors of Boost Libraries Containing Separate Source

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.

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.

BOOST_DISABLE_EXPLICIT_SYMBOL_VISIBILITY

Disables the effect of the BOOST_SYMBOL_EXPORT, BOOST_SYMBOL_IMPORT and BOOST_SYMBOL_VISIBLE macros, in order to revert to the default compiler behaviour. Note that this option should never be used if Boost libraries are being linking against dynamically, or if you are building a shared library that exposes Boost types in its public API. It is however advisable when statically-linking against Boost to prevent Boost symbols from leaking from the binary: for instance because you are building a plug-in for a software which may itself use Boost which could cause ODR conflicts.

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()
{
  ...
}
...

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.

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:

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>
...

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