gcc/libstdc++-v3/docs/configopts.html

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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/libstdc++/configopts.html">
   http://gcc.gnu.org/libstdc++/configopts.html</A>.
</P>

<P>To the <A HREF="index.html">libstdc++-v3 homepage</A>.


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<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 the latest
   snapshot, 2.90.8.
</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 &quot;powerpc-elf&quot; will have
        libstdc++ built many different ways:  &quot;-msoft-float&quot;
        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 &quot;long long&quot; type was introduced in C99.  It is
        provided as a GNU extension to C++98 in g++.  This flag builds
        support for &quot;long long&quot; 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=&lt;include-files dir&gt;</TT>
 <DD><P>Adds support for named libstdc++ include directory.  For instance,
        the following puts all the libstdc++ headers into a directory
        called &quot;2.97-20001008&quot; instead of the usual
        &quot;g++-v3&quot;.
        <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>
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   <A HREF="index.html">to the homepage</A>.
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