source directory and then type: <spanclass="command"><strong>./configure --help</strong></span>.
</p><divclass="variablelist"><dlclass="variablelist"><dt><spanclass="term"><codeclass="code">--enable-multilib</code>[default]</span></dt><dd><p>This is part of the generic multilib support for building cross
compilers. As such, targets like "powerpc-elf" will have
libstdc++ built many different ways: "-msoft-float"
and not, etc. A different libstdc++ will be built for each of
the different multilib versions. This option is on by default.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-sjlj-exceptions</code></span></dt><dd><p>Forces old, set-jump/long-jump exception handling model. If
at all possible, the new, frame unwinding exception handling routines
should be used instead, as they significantly reduce both
runtime memory usage and executable size. This option can
change the library ABI.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-version-specific-runtime-libs</code></span></dt><dd><p>Specify that run-time libraries should be installed in the
<codeclass="literal">--with-gxx-include-dir=</code><codeclass="filename">dirname</code> during configuration.
</p></dd><dt><spanclass="term"><codeclass="code">--with-gxx-include-dir=<include-files dir></code></span></dt><dd><p>Adds support for named libstdc++ include directory. For instance,
the following puts all the libstdc++ headers into a directory
called "4.4-20090404" instead of the usual
"c++/(version)".
</p><preclass="programlisting">
--with-gxx-include-dir=/foo/H-x86-gcc-3-c-gxx-inc/include/4.4-20090404</pre></dd><dt><spanclass="term"><codeclass="code">--enable-cstdio</code></span></dt><dd><p>This is an abbreviated form of <codeclass="code">'--enable-cstdio=stdio'</code>
(described next).
</p></dd><dt><spanclass="term"><codeclass="code">--enable-cstdio=OPTION</code></span></dt><dd><p>Select a target-specific I/O package. At the moment, the only
choice is to use 'stdio', a generic "C" abstraction.
The default is 'stdio'. This option can change the library ABI.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-clocale</code></span></dt><dd><p>This is an abbreviated form of <codeclass="code">'--enable-clocale=generic'</code>
(described next).
</p></dd><dt><spanclass="term"><codeclass="code">--enable-clocale=OPTION</code></span></dt><dd><p>Select a target-specific underlying locale package. The
choices are 'ieee_1003.1-2001' to specify an X/Open, Standard Unix
(IEEE Std. 1003.1-2001) model based on langinfo/iconv/catgets,
'gnu' to specify a model based on functionality from the GNU C
</p></dd><dt><spanclass="term"><codeclass="code">--enable-libstdcxx-allocator=OPTION </code></span></dt><dd><p>Select a target-specific underlying std::allocator. The
choices are 'new' to specify a wrapper for new, 'malloc' to
specify a wrapper for malloc, 'mt' for a fixed power of two allocator,
'pool' for the SGI pooled allocator or 'bitmap' for a bitmap allocator.
See this page for more information on allocator
<aclass="link"href="memory.html#allocator.ext"title="Extension Allocators">extensions</a>. This option
can change the library ABI.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-cheaders=OPTION</code></span></dt><dd><p>This allows the user to define the approach taken for C header
compatibility with C++. Options are c, c_std, and c_global.
These correspond to the source directory's include/c,
include/c_std, and include/c_global, and may also include
include/c_compatibility. The default is 'c_global'.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-threads</code></span></dt><dd><p>This is an abbreviated form of <codeclass="code">'--enable-threads=yes'</code>
(described next).
</p></dd><dt><spanclass="term"><codeclass="code">--enable-threads=OPTION</code></span></dt><dd><p>Select a threading library. A full description is
</p></dd><dt><spanclass="term"><codeclass="code">--enable-libstdcxx-threads</code></span></dt><dd><p>Enable C++11 threads support. If not explicitly specified,
the configure process enables it if possible. It defaults to 'off'
on Solaris 9, where it would break symbol versioning. This
</p></dd><dt><spanclass="term"><codeclass="code">--enable-libstdcxx-time=OPTION</code></span></dt><dd><p>Enables link-type checks for the availability of the
clock_gettime clocks, used in the implementation of [time.clock],
and of the nanosleep and sched_yield functions, used in the
implementation of [thread.thread.this] of the 2011 ISO C++ standard.
The choice OPTION=yes checks for the availability of the facilities
desirable because, in glibc, for example, in turn it triggers the
linking of libpthread too, which activates locking, a large overhead
for single-thread programs. OPTION=no skips the tests completely.
The default is OPTION=no.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-libstdcxx-debug</code></span></dt><dd><p>Build separate debug libraries in addition to what is normally built.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-libstdcxx-debug-flags=FLAGS</code></span></dt><dd><p>This option is only valid when <codeclass="code"> --enable-debug </code>
is also specified, and applies to the debug builds only. With
this option, you can pass a specific string of flags to the
compiler to use when building the debug versions of libstdc++.
FLAGS is a quoted string of options, like
</p><preclass="programlisting">
--enable-libstdcxx-debug-flags='-g3 -O1 -fno-inline'</pre></dd><dt><spanclass="term"><codeclass="code">--enable-cxx-flags=FLAGS</code></span></dt><dd><p>With this option, you can pass a string of -f (functionality)
flags to the compiler to use when building libstdc++. This
option can change the library ABI. FLAGS is a quoted string of
</p></dd><dt><spanclass="term"><codeclass="code">--enable-c99</code></span></dt><dd><p>The <spanclass="type">long long</span> type was introduced in C99, along
</p></dd><dt><spanclass="term"><codeclass="code">--enable-wchar_t</code>[default]</span></dt><dd><p>Template specializations for the <spanclass="type">wchar_t</span> type are
</p></dd><dt><spanclass="term"><codeclass="code">--enable-long-long </code></span></dt><dd><p>The <spanclass="type">long long</span> type was introduced in C99. It is
provided as a GNU extension to C++98 in g++. This flag builds
support for "long long" into the library (specialized
templates and the like for iostreams). This option is on by default:
if enabled, users will have to either use the new-style "C"
headers by default (i.e., <cmath> not <math.h>)
or add appropriate compile-time flags to all compile lines to
allow "C" visibility of this feature (on GNU/Linux,
the flag is -D_ISOC99_SOURCE, which is added automatically via
CPLUSPLUS_CPP_SPEC's addition of _GNU_SOURCE).
This option can change the library ABI.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-fully-dynamic-string</code></span></dt><dd><p>This option enables a special version of basic_string avoiding
the optimization that allocates empty objects in static memory.
Mostly useful together with shared memory allocators, see PR
libstdc++/16612 for details.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-concept-checks</code></span></dt><dd><p>This turns on additional compile-time checks for instantiated
library templates, in the form of specialized templates,
can help users discover when they break the rules of the STL, before
their programs run.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-symvers[=style]</code></span></dt><dd><p>In 3.1 and later, tries to turn on symbol versioning in the
shared library (if a shared library has been
requested). Values for 'style' that are currently supported
are 'gnu', 'gnu-versioned-namespace', 'darwin',
'darwin-export', and 'sun'. Both gnu- options require that a recent
version of the GNU linker be in use. Both darwin options are
equivalent. With no style given, the configure script will try
to guess correct defaults for the host system, probe to see if
additional requirements are necessary and present for
activation, and if so, will turn symbol versioning on. This
option can change the library ABI.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-libstdcxx-visibility</code></span></dt><dd><p> In 4.2 and later, enables or disables visibility
attributes. If enabled (as by default), and the compiler seems
capable of passing the simple sanity checks thrown at it, adjusts
items in namespace std, namespace std::tr1, namespace std::tr2,
and namespace __gnu_cxx to have <codeclass="code">visibility ("default")</code>
so that -fvisibility options can be used without affecting the
normal external-visibility of namespace std entities.
Prior to 4.7 this option was spelled <codeclass="code">--enable-visibility</code>.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-libstdcxx-pch</code></span></dt><dd><p>In 3.4 and later, tries to turn on the generation of
stdc++.h.gch, a pre-compiled file including all the standard
C++ includes. If enabled (as by default), and the compiler
seems capable of passing the simple sanity checks thrown at
it, try to build stdc++.h.gch as part of the make process.
In addition, this generated file is used later on (by appending <codeclass="code">
--include bits/stdc++.h </code> to CXXFLAGS) when running the
testsuite.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-extern-template</code>[default]</span></dt><dd><p>Use extern template to pre-instantiate all required
specializations for certain types defined in the standard libraries.
These types include <codeclass="classname">string</code> and dependents like
By default, the library is configured to write descriptive messages
to standard error for certain events such as calling a pure virtual
function or the invocation of the standard terminate handler. Those
messages cause the library to depend on the demangler and standard I/O
facilities, which might be undesirable in a low-memory environment or
when standard error is not available. This option disables those
messages. This option does not change the library ABI.
</p></dd><dt><spanclass="term"><codeclass="code">--enable-vtable-verify</code>[default]</span></dt><dd><p>Use <codeclass="code">-fvtable-verify=std</code> to compile the C++
runtime with instrumentation for vtable verification. All virtual
functions in the standard library will be verified at runtime.
Types impacted include <codeclass="classname">locale</code> and
<codeclass="classname">iostream</code>, and others. Disabling means that
the C++ runtime is compiled without support for vtable
