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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
< a class = "xref" href = "memory.html#allocator.impl" title = "Implementation" > the section called “Implementation”< / a > . The annotations
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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