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All library macros begin with < code class = "code" > _GLIBCXX_< / code > .
< / p > < p >
Furthermore, all pre-processor macros, switches, and
configuration options are gathered in the
file < code class = "filename" > c++config.h< / code > , which
is generated during the libstdc++ configuration and build
process. This file is then included when needed by files part of
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the public libstdc++ API, like
< code class = "filename" > < ios> < / code > . Most of these
macros should not be used by consumers of libstdc++, and are reserved
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for internal implementation use. < span class = "emphasis" > < em > These macros cannot
be redefined< / em > < / span > .
< / p > < p >
A select handful of macros control libstdc++ extensions and extra
features, or provide versioning information for the API. Only
those macros listed below are offered for consideration by the
general public.
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< / p > < p > Below are the macros which users may check for library version
information. < / p > < div class = "variablelist" > < dl class = "variablelist" > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_RELEASE< / code > < / span > < / dt > < dd > < p > The major release number for libstdc++. This macro is defined
to the GCC major version that the libstdc++ headers belong to,
as an integer constant.
When compiling with GCC it has the same value as GCC's pre-defined
macro < span class = "symbol" > __GNUC__< / span > .
This macro can be used when libstdc++ is used with a non-GNU
compiler where < span class = "symbol" > __GNUC__< / span > is not defined, or has a
different value that doesn't correspond to the libstdc++ version.
This macro first appeared in the GCC 7.1 release and is not defined
for GCC 6.x or older releases.
< / p > < / dd > < dt > < span class = "term" > < code class = "code" > __GLIBCXX__< / code > < / span > < / dt > < dd > < p > The revision date of the libstdc++ source code,
in compressed ISO date format, as an unsigned
long. For notes about using this macro and details on the value of
this macro for a particular release, please consult the
< a class = "link" href = "abi.html#abi.versioning.__GLIBCXX__" > ABI History< / a >
appendix.
< / p > < / dd > < / dl > < / div > < p > Below are the macros which users may change with #define/#undef or
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with -D/-U compiler flags. The default state of the symbol is
listed.< / p > < p > < span class = "quote" > “< span class = "quote" > Configurable< / span > ”< / span > (or < span class = "quote" > “< span class = "quote" > Not configurable< / span > ”< / span > ) means
that the symbol is initially chosen (or not) based on
--enable/--disable options at library build and configure time
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(documented in
< a class = "link" href = "configure.html" title = "Configure" > Configure< / a > ),
with the various --enable/--disable choices being translated to
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#define/#undef).
< / p > < p > < acronym class = "acronym" > ABI< / acronym > means that changing from the default value may
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mean changing the < acronym class = "acronym" > ABI< / acronym > of compiled code. In other words,
these choices control code which has already been compiled (i.e., in a
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binary such as libstdc++.a/.so). If you explicitly #define or
#undef these macros, the < span class = "emphasis" > < em > headers< / em > < / span > may see different code
paths, but the < span class = "emphasis" > < em > libraries< / em > < / span > which you link against will not.
Experimenting with different values with the expectation of
consistent linkage requires changing the config headers before
building/installing the library.
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< / p > < div class = "variablelist" > < dl class = "variablelist" > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_USE_DEPRECATED< / code > < / span > < / dt > < dd > < p >
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Defined by default. Not configurable. ABI-changing. Turning this off
removes older ARM-style iostreams code, and other anachronisms
from the API. This macro is dependent on the version of the
standard being tracked, and as a result may give different results for
< code class = "code" > -std=c++98< / code > and < code class = "code" > -std=c++11< / code > . This may
be useful in updating old C++ code which no longer meet the
requirements of the language, or for checking current code
against new language standards.
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_USE_CXX11_ABI< / code > < / span > < / dt > < dd > < p >
Defined to the value < code class = "literal" > 1< / code > by default.
Configurable via < code class = "code" > --disable-libstdcxx-dual-abi< / code >
and/or < code class = "code" > --with-default-libstdcxx-abi< / code > .
ABI-changing.
When defined to a non-zero value the library headers will use the
new C++11-conforming ABI introduced in GCC 5, rather than the older
ABI introduced in GCC 3.4. This changes the definition of several
class templates, including < code class = "classname" > std:string< / code > ,
< code class = "classname" > std::list< / code > and some locale facets.
For more details see < a class = "xref" href = "using_dual_abi.html" title = "Dual ABI" > Dual ABI< / a > .
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_CONCEPT_CHECKS< / code > < / span > < / dt > < dd > < p >
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Undefined by default. Configurable via
< code class = "code" > --enable-concept-checks< / code > . When defined, performs
compile-time checking on certain template instantiations to
detect violations of the requirements of the standard. This
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macro has no effect for freestanding implementations.
This is described in more detail in
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< a class = "link" href = "ext_compile_checks.html" title = "Chapter > Compile Time Checks< / a > .
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_ASSERTIONS< / code > < / span > < / dt > < dd > < p >
Undefined by default. When defined, enables extra error checking in
the form of precondition assertions, such as bounds checking in
strings and null pointer checks when dereferencing smart pointers.
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_DEBUG< / code > < / span > < / dt > < dd > < p >
Undefined by default. When defined, compiles user code using
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the < a class = "link" href = "debug_mode.html" title = "Chapter > debug mode< / a > .
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When defined, < code class = "code" > _GLIBCXX_ASSERTIONS< / code > is defined
automatically, so all the assertions enabled by that macro are also
enabled in debug mode.
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_DEBUG_PEDANTIC< / code > < / span > < / dt > < dd > < p >
Undefined by default. When defined while compiling with
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the < a class = "link" href = "debug_mode.html" title = "Chapter > debug mode< / a > , makes
the debug mode extremely picky by making the use of libstdc++
extensions and libstdc++-specific behavior into errors.
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_PARALLEL< / code > < / span > < / dt > < dd > < p > Undefined by default. When defined, compiles user code
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using the < a class = "link" href = "parallel_mode.html" title = "Chapter > parallel
mode< / a > .
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_PARALLEL_ASSERTIONS< / code > < / span > < / dt > < dd > < p > Undefined by default, but when any parallel mode header is included
this macro will be defined to a non-zero value if
< code class = "code" > _GLIBCXX_ASSERTIONS< / code > has a non-zero value, otherwise to zero.
When defined to a non-zero value, it enables extra error checking and
assertions in the parallel mode.
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_PROFILE< / code > < / span > < / dt > < dd > < p > Undefined by default. When defined, compiles user code
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using the < a class = "link" href = "profile_mode.html" title = "Chapter > profile
mode< / a > .
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > __STDCPP_WANT_MATH_SPEC_FUNCS__< / code > < / span > < / dt > < dd > < p > Undefined by default. When defined to a non-zero integer constant,
enables support for ISO/IEC 29124 Special Math Functions.
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< / p > < / dd > < dt > < span class = "term" > < code class = "code" > _GLIBCXX_SANITIZE_VECTOR< / code > < / span > < / dt > < dd > < p >
Undefined by default. When defined, < code class = "classname" > std::vector< / code >
operations will be annotated so that AddressSanitizer can detect
invalid accesses to the unused capacity of a
< code class = "classname" > std::vector< / code > . These annotations are only
enabled for
< code class = "classname" > std::vector< T, std::allocator< T> > < / code >
and only when < code class = "classname" > std::allocator< / code > is derived from
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< a class = "link" href = "memory.html#allocator.ext" title = "Extension Allocators" > < code class = "classname" > new_allocator< / code >
or < code class = "classname" > malloc_allocator< / code > < / a > . The annotations
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must be present on all vector operations or none, so this macro must
be defined to the same value for all translation units that create,
destroy or modify vectors.
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