All library macros begin with _GLIBCXX_.
Furthermore, all pre-processor macros, switches, and
configuration options are gathered in the
file c++config.h, which
is generated during the libstdc++ configuration and build
process. This file is then included when needed by files part of
the public libstdc++ API, like
<ios>. Most of these
macros should not be used by consumers of libstdc++, and are reserved
for internal implementation use. These macros cannot
be redefined.
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.
Below are the macros which users may check for library version information.
_GLIBCXX_RELEASEThe 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 __GNUC__. This macro can be used when libstdc++ is used with a non-GNU compiler where __GNUC__ 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.
__GLIBCXX__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 ABI History appendix.
Below are the macros which users may change with #define/#undef or with -D/-U compiler flags. The default state of the symbol is listed.
“Configurable” (or “Not configurable”) means that the symbol is initially chosen (or not) based on --enable/--disable options at library build and configure time (documented in Configure), with the various --enable/--disable choices being translated to #define/#undef).
ABI means that changing from the default value may mean changing the ABI of compiled code. In other words, these choices control code which has already been compiled (i.e., in a binary such as libstdc++.a/.so). If you explicitly #define or #undef these macros, the headers may see different code paths, but the libraries 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.
_GLIBCXX_USE_DEPRECATED
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
-std=c++98 and -std=c++11. 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.
_GLIBCXX_USE_CXX11_ABI
Defined to the value 1 by default.
Configurable via --disable-libstdcxx-dual-abi
and/or --with-default-libstdcxx-abi.
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 std:string,
std::list and some locale facets.
For more details see Dual ABI.
_GLIBCXX_CONCEPT_CHECKS
Undefined by default. Configurable via
--enable-concept-checks. When defined, performs
compile-time checking on certain template instantiations to
detect violations of the requirements of the standard. This
macro has no effect for freestanding implementations.
This is described in more detail in
Compile Time Checks.
_GLIBCXX_ASSERTIONSUndefined 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.
_GLIBCXX_DEBUG
Undefined by default. When defined, compiles user code using
the debug mode.
When defined, _GLIBCXX_ASSERTIONS is defined
automatically, so all the assertions enabled by that macro are also
enabled in debug mode.
_GLIBCXX_DEBUG_PEDANTICUndefined by default. When defined while compiling with the debug mode, makes the debug mode extremely picky by making the use of libstdc++ extensions and libstdc++-specific behavior into errors.
_GLIBCXX_PARALLELUndefined by default. When defined, compiles user code using the parallel mode.
_GLIBCXX_PARALLEL_ASSERTIONSUndefined by default, but when any parallel mode header is included
this macro will be defined to a non-zero value if
_GLIBCXX_ASSERTIONS 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.
_GLIBCXX_PROFILEUndefined by default. When defined, compiles user code using the profile mode.
__STDCPP_WANT_MATH_SPEC_FUNCS__Undefined by default. When defined to a non-zero integer constant, enables support for ISO/IEC 29124 Special Math Functions.