Boost C++ Libraries

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Boost Macro Reference

Macros that describe defects
Macros that describe optional features
Macros that describe possible C++0x features
Macros that describe C++0x features not supported
Boost Helper Macros
Boost Informational Macros
Macros for libraries with separate source code

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

Macro

Section

Description

BOOST_BCB_PARTIAL_SPECIALIZATION_BUG

Compiler

The compiler exibits 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_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_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_EXPLICIT_FUNCTION_TEMPLATE_ARGUMENTS

Compiler

Can only use deduced template arguments when calling function template instantiations.

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.

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_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_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.

BOOST_NO_SFINAE_EXPR

Compiler

The compiler does not support usage of SFINAE with arbitrary expressions.

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.

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_DECLSPEC

Compiler

The compiler uses __declspec(dllexport) and __declspec(dllimport) to export/import symbols from dll's.

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_FTIME

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_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_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>.

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>.

BOOST_HAS_TR1_RESULT_OF

Standard library

The library has a TR1 conforming result_of template in <functional>.

BOOST_HAS_TR1_MEM_FN

Standard library

The library has a TR1 conforming mem_fn function template in <functional>.

BOOST_HAS_TR1_BIND

Standard library

The library has a TR1 conforming bind function template in <functional>.

BOOST_HAS_TR1_FUNCTION

Standard library

The library has a TR1 conforming function class template in <functional>.

BOOST_HAS_TR1_HASH

Standard library

The library has a TR1 conforming hash function template in <functional>.

BOOST_HAS_TR1_SHARED_PTR

Standard library

The library has a TR1 conforming shared_ptr class template in <memory>.

BOOST_HAS_TR1_RANDOM

Standard library

The library has a TR1 conforming version of <random>.

BOOST_HAS_TR1_REGEX

Standard library

The library has a TR1 conforming version of <regex>.

BOOST_HAS_TR1_TUPLE

Standard library

The library has a TR1 conforming version of <tuple>.

BOOST_HAS_TR1_TYPE_TRAITS

Standard library

The library has a TR1 conforming version of <type_traits>.

BOOST_HAS_TR1_UTILITY

Standard library

The library has the TR1 additions to <utility> (tuple interface to std::pair).

BOOST_HAS_TR1_UNORDERED_MAP

Standard library

The library has a TR1 conforming version of <unordered_map>.

BOOST_HAS_TR1_UNORDERED_SET

Standard library

The library has a TR1 conforming version of <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 that are likely to be included in the upcoming ISO C++ standard, C++0x, but have not yet been approved for inclusion in the language.

Macro

Description

BOOST_HAS_CONCEPTS

The compiler supports concepts.

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

Macro

Description

BOOST_NO_0X_HDR_ARRAY

The standard library does not provide header <array>.

BOOST_NO_0X_HDR_CHRONO

The standard library does not provide header <chrono>.

BOOST_NO_0X_HDR_CODECVT

The standard library does not provide header <codecvt>.

BOOST_NO_0X_HDR_CONCEPTS

The standard library does not provide header <concepts>.

BOOST_NO_0X_HDR_CONDITION_VARIABLE

The standard library does not provide header <condition_variable>.

BOOST_NO_0X_HDR_CONTAINER_CONCEPTS

The standard library does not provide header <container_concepts>.

BOOST_NO_0X_HDR_FORWARD_LIST

The standard library does not provide header <forward_list>.

BOOST_NO_0X_HDR_FUTURE

The standard library does not provide header <future>.

BOOST_NO_0X_HDR_INITIALIZER_LIST

The standard library does not provide header <initializer_list>.

BOOST_NO_0X_HDR_ITERATOR_CONCEPTS

The standard library does not provide header <iterator_concepts>.

BOOST_NO_0X_HDR_MEMORY_CONCEPTS

The standard library does not provide header <memory_concepts>.

BOOST_NO_0X_HDR_MUTEX

The standard library does not provide header <mutex>.

BOOST_NO_0X_HDR_RANDOM

The standard library does not provide header <random>.

BOOST_NO_0X_HDR_RATIO

The standard library does not provide header <ratio>.

BOOST_NO_0X_HDR_REGEX

The standard library does not provide header <regex>.

BOOST_NO_0X_HDR_SYSTEM_ERROR

The standard library does not provide header <system_error>.

BOOST_NO_0X_HDR_THREAD

The standard library does not provide header <thread>.

BOOST_NO_0X_HDR_TUPLE

The standard library does not provide header <tuple>.

BOOST_NO_0X_HDR_TYPE_TRAITS

The standard library does not provide header <type_traits>.

BOOST_NO_0X_HDR_UNORDERED_MAP

The standard library does not provide header <unordered_map>.

BOOST_NO_0X_HDR_UNORDERED_SET

The standard library does not provide header <unordered_set>.

BOOST_NO_AUTO_DECLARATIONS

The compiler does not support type deduction for variables declared with the auto keyword (auto var = ...;).

BOOST_NO_AUTO_MULTIDECLARATIONS

The compiler does not support type deduction for multiple variables declared with the auto keyword (auto var = ..., *ptr = ...;).

BOOST_NO_CHAR16_T

The compiler does not support type char16_t.

BOOST_NO_CHAR32_T

The compiler does not support type char32_t.

BOOST_NO_CONCEPTS

The compiler does not support Concepts.

BOOST_NO_TEMPLATE_ALIASES

The compiler does not support template aliases.

BOOST_NO_CONSTEXPR

The compiler does not support constexpr.

BOOST_NO_DECLTYPE

The compiler does not support decltype.

BOOST_NO_DEFAULTED_FUNCTIONS

The compiler does not support defaulted (= default) functions.

BOOST_NO_DELETED_FUNCTIONS

The compiler does not support deleted (= delete) functions.

BOOST_NO_EXPLICIT_CONVERSION_OPERATIONS

The compiler does not support explicit conversion operators (explicit operator T()).

BOOST_NO_EXTERN_TEMPLATE

The compiler does not support explicit instantiation declarations for templates (explicit template).

BOOST_NO_FUNCTION_TEMPLATE_DEFAULT_ARGS

The compiler does not support default template arguments for function templates.

BOOST_NO_INITIALIZER_LISTS

The C++ compiler does not support C++0x initializer lists.

BOOST_NO_LAMBDAS

The compiler does not support Lambdas.

BOOST_NO_LONG_LONG

The compiler does not support long long.

BOOST_NO_NULLPTR

The compiler does not support 'nullptr'.

BOOST_NO_RAW_LITERALS

The compiler does not support raw string literals.

BOOST_NO_RVALUE_REFERENCES

The compiler does not support r-value references.

BOOST_NO_SCOPED_ENUMS

The compiler does not support scoped enumerations (enum class).

BOOST_NO_STATIC_ASSERT

The compiler does not support static_assert.

BOOST_NO_STD_UNORDERD

The standard library does not support <unordered_map> and <unordered_set>.

BOOST_NO_TEMPLATE_ALIASES

The compiler does not support template aliases.

BOOST_NO_UNICODE_LITERALS

The compiler does not support Unicode (u8, u, U) literals.

BOOST_NO_VARIADIC_TEMPLATES

The compiler does not support variadic templates.

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/detail/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/detail/workaround.hpp.

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_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 comforming 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__.

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_INTEL

<boost/config.hpp>

Defined if the compiler is an Intel compiler, takes the same value as the compiler version macro.

BOOST_WINDOWS

<boost/config.hpp>

Defined if the Windows platfrom 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.

The following macros and helper headers are of use to authors whose libraries include separate source code, and are intended to address two issues: fixing the ABI of the compiled library, and selecting which compiled library to link against based upon the compilers settings.

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).

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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