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<META NAME="AUTHOR" CONTENT="pme@sources.redhat.com (Phil Edwards)">
<META NAME="KEYWORDS" CONTENT="libstdc++, libstdc++-v3, GCC, g++">
<META NAME="DESCRIPTION" CONTENT="Configuration options for libstdc++-v3.">
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<TITLE>libstdc++-v3 configure options</TITLE>
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<H1 CLASS="centered"><A NAME="top">Interesting <TT>configure</TT>
options</A></H1>
<P>The latest version of this document is always available at
<A HREF="http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html">
http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html</A>.
</P>
<P>To the <A HREF="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</A>.
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<HR>
<P>Here are some of the non-obvious options to libstdc++'s configure.
Keep in mind that
<!-- This SECnn should be the "Choosing Package Options" section. -->
<A HREF="http://sources.redhat.com/autoconf/autoconf.html#SEC74">they
all have opposite forms as well</A>
(enable/disable and with/without). The defaults are for current
development sources.
</P>
<P>The canonical way to find out the configure options that are
available for a given set of libstdc++ sources is to go to the
source directory and then type:<TT> ./configure --help</TT>
<DL>
<DT><TT>--enable-multilib </TT>[default]
<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>
<DT><TT>--enable-debug </TT>
<DD><P>The configure script will automatically detect the highest level
of optimization that the compiler in use can use (certain
versions of g++ will ICE if given the <TT>-O2</TT> option, but
this is fixed in later versions of the compiler). This --enable
flag will disable all optimizations and instruct the compiler to
emit as much extra debugging information as it can, for use
inside GDB.
</P>
<DT><TT>--enable-cstdio </TT>[default]
<DD><P>This is an abbreviated form of <TT>'--enable-cstdio=libio'</TT>
(described next).
</P>
<DT><TT>--enable-cstdio=LIB </TT>
<DD><P>Select a target-specific I/O package. As of libstdc++-v3
snapshot 2.90.8, the choices are 'libio' to specify the GNU
I/O package (from
<A HREF="http://sources.redhat.com/glibc/">glibc</A>, the
GNU C library), or 'stdio' to use a generic "C" abstraction.
</P>
<DT><TT>--enable-long-long </TT>
<DD><P>The "long long" 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).
</P>
<DT><TT>--enable-cshadow-headers </TT>
<DD><P>This turns on the code to construct shadowed C headers, and to
use c headers in the std:: namespace. Very experimental as of
this writing.
</P>
<DT><TT>--enable-threads </TT>
<DD><P>This is an abbreviated form of <TT>'--enable-threads=yes'</TT>
(described next).
</P>
<DT><TT>--enable-threads=LIB </TT>
<DD><P>Select a threading library. As of libstdc++-v3 snapshot 2.90.8,
the choices are:
'yes' for some kind of default (hmmmmm);
'decosf1', 'irix', 'mach', 'os2', 'posix'/'pthreads'
(same thing),
'solaris', 'win32', 'dce', or 'vxworks' to select the
corresponding interface;
and 'single', 'no', or 'none' for the null-case,
single-threaded library.
</P>
<P>All of this is currently undergoing a lot of changes. As of
2.90.8, 'single' and 'posix' are the only implemented models.
</P>
<DT><TT>--enable-version-specific-runtime-libs </TT>
<DD><P>Specify that run-time libraries should be installed in the
compiler-specific subdirectory (i.e.,
<TT>$(libdir)/gcc-lib/$(target_alias)/$(gcc_version)</TT>)
instead of <TT>$(libdir)</TT>. This option is useful if you
intend to use several versions of gcc in parallel. In addition,
libstdc++'s include files will be installed in
<TT>$(libdir)/gcc-lib/$(target_alias)/$(gcc_version)/include/g++</TT>,
unless you also specify
<TT>--with-gxx-include-dir=_dirname_</TT> during configuration.
</P>
<DT><TT>--with-gxx-include-dir=<include-files dir></TT>
<DD><P>Adds support for named libstdc++ include directory. For instance,
the following puts all the libstdc++ headers into a directory
called "2.97-20001008" instead of the usual
"g++-v3".
<PRE>
--with-gxx-include-dir=/foo/H-x86-gcc-3-c-gxx-inc/include/2.97-20001008</PRE>
</P>
<DT><TT>--enable-cxx-flags=FLAGS</TT>
<DD><P>With this option, you can pass a string of -f (functionality)
flags to the compiler to use when building libstdc++. FLAGS
is a quoted string of options, like
<PRE>
--enable-cxx-flags='-fsquangle -fvtable-gc -ansi'</PRE>
Note that the flags don't necessarily have to all be -f flags,
as shown, but usually those are the ones that will make sense
for experimentation and configure-time overriding.
</P>
<P>The advantage of --enable-cxx-flags over setting CXXFLAGS in
the 'make' environment is that, if libgcc is automatically
rebuilt, the same flags will be used when compiling those files
as well, so that everything matches.
</P>
<P>Fun flags to try might include combinations of
<PRE>
-fstrict-aliasing
-fnew-abi
-fnew-exceptions
-ffunction-sections
-fvtable-gc</PRE>
and -fno- forms of the same. Tell us (the mailing list) if
you discover more!
</P>
<DT><TT>--enable-wchar </TT>[default]
<DD><P>Certain template specializations are required for wide character
conversion support. This is tricky and currently changing rapidly,
and can cause problems on new platforms. Disabling wide character
specializations is useful for initial porting steps, but builds
only a subset of what is required by ISO.
</P>
</DL>
</P>
<P>Return <A HREF="#top">to the top of the page</A> or
<A HREF="http://gcc.gnu.org/libstdc++/">to the homepage</A>.
</P>
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