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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
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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.">
<META NAME="GENERATOR" CONTENT="vi and eight fingers">
<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>.
<!-- ####################################################### -->
<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>
<DD><P>This is an abbreviated form of <TT>'--enable-cstdio=stdio'</TT>
(described next).
</P>
<DT><TT>--enable-cstdio=LIB </TT>
<DD><P>Select a target-specific I/O package. As of libstdc++-v3
snapshot 2.91, 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. The default is 'stdio'. A longer explanation
is <A HREF="explanations.html#cstdio">here</A>.
</P>
<DT><TT>--enable-sjlj-exceptions </TT>
<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.
</P>
<DT><TT>--enable-clocale </TT>
<DD><P>This is an abbreviated form of <TT>'--enable-clocale=generic'</TT>
(described next).
</P>
<DT><TT>--enable-clocale=MODEL </TT>
<DD><P>Select a target-specific underlying locale package. The choices
are 'gnu' to specify an X/Open (IEEE Std. 1003.1-200x) model based
on langinfo/iconv (from
<A HREF="http://sources.redhat.com/glibc/">glibc</A>, the GNU C
library), or 'generic' to use a generic "C" abstraction
which consists of "C" locale info. The default is 'generic'.
</P>
<DT><TT>--enable-c99 </TT>
<DD><P>The "long long" type was introduced in C99, along
with bunches of other functions for wide characters, and math
classification macros, etc. If enabled, all C99 functions not
specified by the C++ standard will be put into <TT>namespace
c99</TT>, and then all names in the c99 namespace will be injected
into namespace std, so that C99 functions can be used "as
if" they were in the C++ standard (as they will eventually
be in some future revision of the standard, without a doubt).
By default, C99 support is on, assuming the configure probes find
all the necessary functions and bits necessary.
</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 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).
</P>
<DT><TT>--enable-cheaders=OPTION </TT>
<DD><P>This allows the user to define what kind of C headers are
used. Options are: c, c_std, and c_shadow. These correspond
to the source directory's include/c, include/c_std, and
include/c_shadow directories. The default is c_std.
</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 2.91,
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
2.91, 'single' and 'posix' are the only implemented
models. Default is single.
</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=<EM>dirname</EM></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='-fvtable-gc -fomit-frame-pointer -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 files are 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
-fno-exceptions
-ffunction-sections
-fvtable-gc</PRE>
and opposite forms (-fno-) of the same. Tell us (the mailing
list) if you discover more!
</P>
<DT><TT>--enable-c-mbchar </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. Default is on, but the <TT>--enable-cstdio=stdio </TT>
option currently turns it off.
</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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