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

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  13 <h1 class="centered"><a name="top">Interesting <code>configure</code>
  14 options</a></h1>
  15
  16 <p>The latest version of this document is always available at
  17    <a href="http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html">
  18    http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html</a>.
  19 </p>
  20
  21 <p>To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
  22
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  25 <hr>
  26 <p>Here are some of the non-obvious options to libstdc++'s configure.
  27    Keep in mind that
  28    <!-- This SECnn should be the "Choosing Package Options" section. -->
  29    <a href="http://www.gnu.org/manual/autoconf/html_node/Package-Options.html#Package%20Options">they
  30    all have opposite forms as well</a>
  31    (enable/disable and with/without).  The defaults are for current
  32    development sources.
  33 </p>
  34 <p>The canonical way to find out the configure options that are
  35    available for a given set of libstdc++ sources is to go to the
  36    source directory and then type:<code>  ./configure --help</code>
  37
  38 <dl>
  39  <dt><code>--enable-multilib  </code>[default]
  40  <dd><p>This is part of the generic multilib support for building cross
  41         compilers.  As such, targets like &quot;powerpc-elf&quot; will have
  42         libstdc++ built many different ways:  &quot;-msoft-float&quot;
  43         and not, etc.  A different libstdc++ will be built for each of
  44         the different multilib versions.  This option is on by default.
  45      </p>
  46
  47  <dt><code>--enable-debug  </code>
  48  <dd><p>The configure script will automatically detect the highest
  49         level of optimization that the compiler in use can use.
  50         This --enable flag will disable all optimizations and instruct
  51         the compiler to emit as much extra debugging information as it
  52         can, for use inside GDB.  Note this make command, executed in
  53         the build directory, will do much the same thing, without the
  54         configuration difference:
  55         <code>make CXXFLAGS='-g -O0' all</code>
  56      </p>
  57
  58  <dt><code>--enable-cstdio  </code>
  59  <dd><p>This is an abbreviated form of <code>'--enable-cstdio=stdio'</code>
  60         (described next).
  61      </p>
  62
  63  <dt><code>--enable-cstdio=LIB  </code>
  64  <dd><p>Select a target-specific I/O package.  As of libstdc++-v3
  65         snapshot 3.0.96, 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'.  A longer explanation
  70         is <a href="explanations.html#cstdio">here</a>.
  71      </p>
  72
  73  <dt><code>--enable-sjlj-exceptions  </code>
  74  <dd><p>Forces old, set-jump/long-jump exception handling model.  If
  75         at all possible, the new, frame unwinding exception handling routines
  76         should be used instead, as they significantly reduce both runtime
  77         memory usage and executable size.
  78      </p>
  79
  80  <dt><code>--enable-clocale  </code>
  81  <dd><p>This is an abbreviated form of <code>'--enable-clocale=generic'</code>
  82         (described next).
  83      </p>
  84
  85  <dt><code>--enable-clocale=MODEL  </code>
  86  <dd><p>Select a target-specific underlying locale package.  The
  87         choices are 'ieee_1003.1-2001' to specify an X/Open, Standard Unix
  88         (IEEE Std. 1003.1-2001) model based on langinfo/iconv/catgets,
  89         'gnu' to specify a model based on functionality from the GNU C
  90         library (langinfo/iconv/gettext) (from <A
  91         href="http://sources.redhat.com/glibc/">glibc</a>, the GNU C
  92         library), or 'generic' to use a generic &quot;C&quot;
  93         abstraction which consists of &quot;C&quot; locale info.  The
  94         default is 'generic'.
  95      </p>
  96
  97  <dt><code>--enable-c99  </code>
  98  <dd><p>The &quot;long long&quot; type was introduced in C99, along
  99         with many other functions for wide characters, and math
 100         classification macros, etc.  If enabled, all C99 functions not
 101         specified by the C++ standard will be put into <code>namespace
 102         __gnu_cxx</code>, and then all these names will
 103         be injected into namespace std, so that C99 functions can be
 104         used &quot;as if&quot; they were in the C++ standard (as they
 105         will eventually be in some future revision of the standard,
 106         without a doubt).  By default, C99 support is on, assuming the
 107         configure probes find all the necessary functions and bits
 108         necessary.
 109     </p>
 110
 111  <dt><code>--enable-long-long  </code>
 112  <dd><p>The &quot;long long&quot; type was introduced in C99.  It is
 113         provided as a GNU extension to C++98 in g++.  This flag builds
 114         support for &quot;long long&quot; into the library (specialized
 115         templates and the like for iostreams).  This option is on by default:
 116         if enabled, users will have to either use the new-style &quot;C&quot;
 117         headers by default (i.e., &lt;cmath&gt; not &lt;math.h&gt;)
 118         or add appropriate compile-time flags to all compile lines to
 119         allow &quot;C&quot; visibility of this feature (on GNU/Linux,
 120         the flag is -D_ISOC99_SOURCE, which is added automatically via
 121         CPLUSPLUS_CPP_SPEC's addition of _GNU_SOURCE).
 122      </p>
 123
 124  <dt><code>--enable-cheaders=OPTION  </code>
 125  <dd><p>This allows the user to define what kind of C headers are
 126         used.  Options are: c, c_std, and c_shadow. These correspond
 127         to the source directory's include/c, include/c_std, and
 128         include/c_shadow directories.  The default is c_std.
 129      </p>
 130
 131  <dt><code>--enable-threads  </code>
 132  <dd><p>This is an abbreviated form of <code>'--enable-threads=yes'</code>
 133         (described next).
 134      </p>
 135
 136  <dt><code>--enable-threads=LIB  </code>
 137  <dd><p>Select a threading library.  A full description is given in the
 138         general <a href="http://gcc.gnu.org/install/configure.html">compiler
 139         configuration instructions</a>.
 140      </p>
 141
 142  <dt><code>--enable-version-specific-runtime-libs  </code>
 143  <dd><p>Specify that run-time libraries should be installed in the
 144         compiler-specific subdirectory (i.e.,
 145         <code>${libdir}/gcc-lib/${target_alias}/${gcc_version}</code>)
 146         instead of <code>${libdir}</code>.  This option is useful if you
 147         intend to use several versions of gcc in parallel.  In addition,
 148         libstdc++'s include files will be installed in
 149         <code>${libdir}/gcc-lib/${target_alias}/${gcc_version}/include/g++</code>,
 150         unless you also specify
 151        <code>--with-gxx-include-dir=<em>dirname</em></code> during configuration.
 152      </p>
 153
 154  <dt><code>--with-gxx-include-dir=&lt;include-files dir&gt;</code>
 155  <dd><p>Adds support for named libstdc++ include directory.  For instance,
 156         the following puts all the libstdc++ headers into a directory
 157         called &quot;2.97-20001008&quot; instead of the usual
 158         &quot;g++-v3&quot;.
 159         <pre>
 160    --with-gxx-include-dir=/foo/H-x86-gcc-3-c-gxx-inc/include/2.97-20001008</pre>
 161      </p>
 162
 163  <dt><code>--enable-cxx-flags=FLAGS</code>
 164  <dd><p>With this option, you can pass a string of -f (functionality)
 165         flags to the compiler to use when building libstdc++.  FLAGS
 166         is a quoted string of options, like
 167         <pre>
 168   --enable-cxx-flags='-fvtable-gc -fomit-frame-pointer -ansi'</pre>
 169         Note that the flags don't necessarily have to all be -f flags,
 170         as shown, but usually those are the ones that will make sense
 171         for experimentation and configure-time overriding.
 172      </p>
 173      <p>The advantage of --enable-cxx-flags over setting CXXFLAGS in
 174         the 'make' environment is that, if files are automatically
 175         rebuilt, the same flags will be used when compiling those files
 176         as well, so that everything matches.
 177      </p>
 178      <p>Fun flags to try might include combinations of
 179         <pre>
 180   -fstrict-aliasing
 181   -fno-exceptions
 182   -ffunction-sections
 183   -fvtable-gc</pre>
 184         and opposite forms (-fno-) of the same.  Tell us (the libstdc++
 185         mailing list) if you discover more!
 186      </p>
 187
 188  <dt><code>--enable-c-mbchar  </code>[default]
 189  <dd><p>Certain template specializations are required for wide
 190         character conversion support.  This is tricky and currently
 191         changing rapidly, and can cause problems on new platforms.
 192         Disabling wide character specializations is useful for initial
 193         porting steps, but builds only a subset of what is required by
 194         ISO.  By default, this option is on.
 195      </p>
 196
 197  <dt><code>--enable-concept-checks  </code>
 198  <dd><p>This turns on additional compile-time checks for instantiated
 199         library templates, in the form of specialized templates,
 200         <a href="19_diagnostics/howto.html#3">described here</a>.  They
 201         can help users discover when they break the rules of the STL, before
 202         their programs run.
 203      </p>
 204
 205  <dt><code>--enable-symvers[=style]  </code>
 206  <dd><p>In 3.1, tries to turn on symbol versioning in the shared library (if a
 207         shared library has been requested).  The only 'style' currently
 208         supported is 'gnu' which requires that a recent version of the GNU
 209         linker be in use.  With no style given, the configure script will
 210         try to guess if the 'gnu' style can be used, and if so, will turn it
 211         on.  Hopefully people will volunteer to do other 'style' options.
 212      </p>
 213 </dl>
 214 </p>
 215 <p>Return <a href="#top">to the top of the page</a> or
 216    <a href="http://gcc.gnu.org/libstdc++/">to the libstdc++ homepage</a>.
 217 </p>
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