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

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  14 <H1 CLASS="centered"><A NAME="top">Interesting <TT>configure</TT>
  15 options</A></H1>
  16
  17 <P>The latest version of this document is always available at
  18    <A HREF="http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html">
  19    http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html</A>.
  20 </P>
  21
  22 <P>To the <A HREF="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</A>.
  23
  24
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  27 <P>Here are some of the non-obvious options to libstdc++'s configure.
  28    Keep in mind that
  29    <!-- This SECnn should be the "Choosing Package Options" section. -->
  30    <A HREF="http://sources.redhat.com/autoconf/autoconf.html#SEC74">they
  31    all have opposite forms as well</A>
  32    (enable/disable and with/without).  The defaults are for current
  33    development sources.
  34 </P>
  35 <P>The canonical way to find out the configure options that are
  36    available for a given set of libstdc++ sources is to go to the
  37    source directory and then type:<TT>  ./configure --help</TT>
  38
  39 <DL>
  40  <DT><TT>--enable-multilib  </TT>[default]
  41  <DD><P>This is part of the generic multilib support for building cross
  42         compilers.  As such, targets like &quot;powerpc-elf&quot; will have
  43         libstdc++ built many different ways:  &quot;-msoft-float&quot;
  44         and not, etc.  A different libstdc++ will be built for each of
  45         the different multilib versions.  This option is on by default.
  46      </P>
  47
  48  <DT><TT>--enable-debug  </TT>
  49  <DD><P>The configure script will automatically detect the highest level
  50         of optimization that the compiler in use can use (certain
  51         versions of g++ will ICE if given the <TT>-O2</TT> option, but
  52         this is fixed in later versions of the compiler).  This --enable
  53         flag will disable all optimizations and instruct the compiler to
  54         emit as much extra debugging information as it can, for use
  55         inside GDB.
  56      </P>
  57
  58  <DT><TT>--enable-cstdio  </TT>
  59  <DD><P>This is an abbreviated form of <TT>'--enable-cstdio=stdio'</TT>
  60         (described next).
  61      </P>
  62
  63  <DT><TT>--enable-cstdio=LIB  </TT>
  64  <DD><P>Select a target-specific I/O package.  As of libstdc++-v3
  65         snapshot 2.91, the choices are 'libio' to specify the GNU
  66         I/O package (from
  67         <A HREF="http://sources.redhat.com/glibc/">glibc</A>, the
  68         GNU C library), or 'stdio' to use a generic &quot;C&quot;
  69         abstraction.  The default is 'stdio'.
  70      </P>
  71
  72  <DT><TT>--enable-sjlj-exceptions </TT>
  73  <DD><P> Forces old, short-jump/long-jump exception handling model. If
  74  at all possible, the new, frame unwinding exception handling routines
  75  should be used instead, as they significantly reduce both runtime
  76  memory usage and executable size.
  77      </P>
  78
  79
  80  <DT><TT>--enable-clocale  </TT>
  81  <DD><P>This is an abbreviated form of <TT>'--enable-clocale=generic'</TT>
  82         (described next).
  83      </P>
  84
  85  <DT><TT>--enable-clocale=MODEL </TT> <DD><P>Select a target-specific
  86  underlying locale package. The choices are 'gnu' to specify an X/Open
  87  (IEEE Std. 1003.1-200x) model based on langinfo/iconv (from <A
  88  HREF="http://sources.redhat.com/glibc/">glibc</A>, the GNU C
  89  library), or 'generic' to use a generic &quot;C&quot; abstraction
  90  which consists of &quot;C&quot; locale info.  The default is
  91  'generic'.
  92      </P>
  93
  94  <DT><TT>--enable-long-long  </TT>
  95  <DD><P>The &quot;long long&quot; type was introduced in C99.  It is
  96         provided as a GNU extension to C++98 in g++.  This flag builds
  97         support for &quot;long long&quot; into the library
  98         (specialized templates and the like). This option is off by
  99         default:  if enabled, users will have to either use the
 100         new-style &quot;C&quot; headers by default (ie cmath not math.h)
 101         or add appropriate compile-time flags to all compile lines to
 102         allow &quot;C&quot; visibility of this feature (on GNU/Linux,
 103         the flag is -D_ISOC99_SOURCE).
 104      </P>
 105
 106  <DT><TT>--enable-cheaders=OPTION  </TT>
 107  <DD><P>This allows the user to define what kind of C headers are
 108         used.  Options are: c, c_std, and c_shadow. These correspond
 109         to the source directory's include/c, include/c_std, and
 110         include/c_shadow directories.  The default is c_std.
 111      </P>
 112
 113  <DT><TT>--enable-threads  </TT>
 114  <DD><P>This is an abbreviated form of <TT>'--enable-threads=yes'</TT>
 115         (described next).
 116      </P>
 117
 118  <DT><TT>--enable-threads=LIB  </TT>
 119  <DD><P>Select a threading library.  As of libstdc++-v3 snapshot 2.91,
 120         the choices are:
 121         'yes' for some kind of default (hmmmmm);
 122         'decosf1', 'irix', 'mach', 'os2', 'posix'/'pthreads'
 123         (same thing),
 124         'solaris', 'win32', 'dce', or 'vxworks' to select the
 125         corresponding interface;
 126         and 'single', 'no', or 'none' for the null-case,
 127         single-threaded library.
 128      </P>
 129      <P>All of this is currently undergoing a lot of changes.  As of
 130         2.91, 'single' and 'posix' are the only implemented
 131         models.  Default is single.
 132      </P>
 133
 134  <DT><TT>--enable-version-specific-runtime-libs  </TT>
 135  <DD><P>Specify that run-time libraries should be installed in the
 136        compiler-specific subdirectory (i.e.,
 137        <TT>$(libdir)/gcc-lib/$(target_alias)/$(gcc_version)</TT>)
 138        instead of <TT>$(libdir)</TT>.  This option is useful if you
 139        intend to use several versions of gcc in parallel.  In addition,
 140        libstdc++'s include files will be installed in
 141        <TT>$(libdir)/gcc-lib/$(target_alias)/$(gcc_version)/include/g++</TT>,
 142        unless you also specify
 143        <TT>--with-gxx-include-dir=_dirname_</TT> during configuration.
 144      </P>
 145
 146  <DT><TT>--with-gxx-include-dir=&lt;include-files dir&gt;</TT>
 147  <DD><P>Adds support for named libstdc++ include directory.  For instance,
 148         the following puts all the libstdc++ headers into a directory
 149         called &quot;2.97-20001008&quot; instead of the usual
 150         &quot;g++-v3&quot;.
 151         <PRE>
 152    --with-gxx-include-dir=/foo/H-x86-gcc-3-c-gxx-inc/include/2.97-20001008</PRE>
 153      </P>
 154
 155  <DT><TT>--enable-cxx-flags=FLAGS</TT>
 156  <DD><P>With this option, you can pass a string of -f (functionality)
 157         flags to the compiler to use when building libstdc++.  FLAGS
 158         is a quoted string of options, like
 159         <PRE>
 160   --enable-cxx-flags='-fvtable-gc -fomit-frame-pointer -ansi'</PRE>
 161         Note that the flags don't necessarily have to all be -f flags,
 162         as shown, but usually those are the ones that will make sense
 163         for experimentation and configure-time overriding.
 164      </P>
 165      <P>The advantage of --enable-cxx-flags over setting CXXFLAGS in
 166         the 'make' environment is that, if files are automatically
 167         rebuilt, the same flags will be used when compiling those files
 168         as well, so that everything matches.
 169      </P>
 170      <P>Fun flags to try might include combinations of
 171         <PRE>
 172   -fstrict-aliasing
 173   -fno-exceptions
 174   -ffunction-sections
 175   -fvtable-gc</PRE>
 176         and opposite forms (-fno-) of the same.  Tell us (the mailing
 177         list) if you discover more!
 178      </P>
 179
 180  <DT><TT>--enable-c-mbchar  </TT>[default]
 181  <DD><P>Certain template specializations are required for wide
 182         character conversion support.  This is tricky and currently
 183         changing rapidly, and can cause problems on new platforms.
 184         Disabling wide character specializations is useful for initial
 185         porting steps, but builds only a subset of what is required by
 186         ISO.  Default is on, but the <TT>--enable-cstdio=stdio </TT>
 187         option currently turns it off.
 188      </P>
 189 </DL>
 190 </P>
 191 <P>Return <A HREF="#top">to the top of the page</A> or
 192    <A HREF="http://gcc.gnu.org/libstdc++/">to the homepage</A>.
 193 </P>
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