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<head>
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<meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
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<meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++" />
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<meta name="DESCRIPTION" content="Configuration options for libstdc++-v3." />
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<meta name="GENERATOR" content="vi and eight fingers" />
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<title>libstdc++-v3 configure options</title>
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<link rel="StyleSheet" href="lib3styles.css" type="text/css" />
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<link rel="Copyright" href="17_intro/license.html" type="text/html" />
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</head>
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<body>
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<h1 class="centered"><a name="top">Interesting <code>configure</code>
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options</a></h1>
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<p class="fineprint"><em>
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The latest version of this document is always available at
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<a href="http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html">
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http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html</a>.
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</em></p>
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<p><em>
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To the <a href="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</a>.
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</em></p>
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<!-- ####################################################### -->
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<hr />
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<p>Here are some of the non-obvious options to libstdc++'s configure.
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Keep in mind that
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<!-- This SECnn should be the "Choosing Package Options" section. -->
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<a href="http://www.gnu.org/software/autoconf/manual/autoconf-2.57/html_node/autoconf_131.html#SEC131">they
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all have opposite forms as well</a>
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(enable/disable and with/without). The defaults are for <strong>current
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development sources</strong>, which may be different than those for
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released versions.
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</p>
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<p>The canonical way to find out the configure options that are
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available for a given set of libstdc++ sources is to go to the
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source directory and then type:<code> ./configure --help</code>
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</p>
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<dl>
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<dt><code>--enable-multilib </code>[default]</dt>
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<dd><p>This is part of the generic multilib support for building cross
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compilers. As such, targets like "powerpc-elf" will have
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libstdc++ built many different ways: "-msoft-float"
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and not, etc. A different libstdc++ will be built for each of
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the different multilib versions. This option is on by default.
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</p>
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</dd>
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<dt><code>--enable-sjlj-exceptions </code></dt>
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<dd><p>Forces old, set-jump/long-jump exception handling model. If
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at all possible, the new, frame unwinding exception handling routines
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should be used instead, as they significantly reduce both
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runtime memory usage and executable size. This option can
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change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-version-specific-runtime-libs </code></dt>
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<dd><p>Specify that run-time libraries should be installed in the
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compiler-specific subdirectory (i.e.,
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<code>${libdir}/gcc-lib/${target_alias}/${gcc_version}</code>)
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instead of <code>${libdir}</code>. This option is useful if you
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intend to use several versions of gcc in parallel. In addition,
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libstdc++'s include files will be installed in
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<code>${libdir}/gcc-lib/${target_alias}/${gcc_version}/include/g++</code>,
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unless you also specify
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<code>--with-gxx-include-dir=<em>dirname</em></code> during configuration.
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</p>
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</dd>
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<dt><code>--with-gxx-include-dir=<include-files dir></code></dt>
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<dd><p>Adds support for named libstdc++ include directory. For instance,
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the following puts all the libstdc++ headers into a directory
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called "2.97-20001008" instead of the usual
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"c++/(version)".
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</p>
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<pre>
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--with-gxx-include-dir=/foo/H-x86-gcc-3-c-gxx-inc/include/2.97-20001008</pre> </dd>
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<dt><code>--enable-cstdio </code></dt>
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<dd><p>This is an abbreviated form of <code>'--enable-cstdio=stdio'</code>
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(described next). This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-cstdio=OPTION </code></dt>
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<dd><p>Select a target-specific I/O package. At the moment, the only
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choice is to use 'stdio', a generic "C" abstraction.
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The default is 'stdio'. A longer explanation is <a
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href="explanations.html#cstdio">here</a>.
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</p>
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</dd>
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<dt><code>--enable-clocale </code></dt>
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<dd><p>This is an abbreviated form of <code>'--enable-clocale=generic'</code>
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(described next). This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-clocale=OPTION </code></dt>
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<dd><p>Select a target-specific underlying locale package. The
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choices are 'ieee_1003.1-2001' to specify an X/Open, Standard Unix
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(IEEE Std. 1003.1-2001) model based on langinfo/iconv/catgets,
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'gnu' to specify a model based on functionality from the GNU C
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library (langinfo/iconv/gettext) (from <a
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href="http://sources.redhat.com/glibc/">glibc</a>, the GNU C
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library), or 'generic' to use a generic "C"
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abstraction which consists of "C" locale info.
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</p>
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<p>As part of the configuration process, the "C" library is
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probed both for sufficient vintage, and installed locale
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data. If either of these elements are not present, the C++
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locale model default to 'generic.' On glibc-based systems of
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version 2.2.5 and above with installed locale files, 'gnu' is
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automatically selected.
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</p>
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</dd>
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<dt><code>--enable-libstdcxx-allocator </code></dt>
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<dd><p>This is an abbreviated form of
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<code>'--enable-libstdcxx-allocator=auto'</code> (described
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next). This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-libstdcxx-allocator=OPTION </code></dt>
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<dd><p>Select a target-specific underlying std::allocator. The
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choices are 'new' to specify a wrapper for new, 'malloc' to
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specify a wrapper for malloc, 'mt' for a fixed power of two allocator
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(<a href="ext/mt_allocator.html">documented</a> under extensions),
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'pool' for the SGI pooled allocator or 'bitmap' for a bitmap allocator.
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This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-cheaders=OPTION </code></dt>
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<dd><p>This allows the user to define what kind of C headers are
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used. Options are c and c_std. These correspond to the source
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directory's include/c and include/c_std. The default is c_std.
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</p>
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</dd>
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<dt><code>--enable-threads </code></dt>
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<dd><p>This is an abbreviated form of <code>'--enable-threads=yes'</code>
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(described next). This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-threads=OPTION </code></dt>
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<dd><p>Select a threading library. A full description is given in the
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general <a href="http://gcc.gnu.org/install/configure.html">compiler
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configuration instructions</a>.
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</p>
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</dd>
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<dt><code>--enable-libstdcxx-debug </code></dt>
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<dd><p>Build separate debug libraries in addition to what is normally built.
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By default, the debug libraries are compiled with
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<code> CXXFLAGS='-g3 -O0'</code>
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, are installed in <code>${libdir}/debug</code>, and have the
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same names and versioning information as the non-debug
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libraries. This option is off by default.
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</p>
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<p>Note this make command, executed in
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the build directory, will do much the same thing, without the
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configuration difference and without building everything twice:
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<code>make CXXFLAGS='-g3 -O0' all</code>
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</p>
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</dd>
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<dt><code>--enable-libstdcxx-debug-flags=FLAGS</code></dt>
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<dd><p>This option is only valid when <code> --enable-debug </code>
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is also specified, and applies to the debug builds only. With
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this option, you can pass a specific string of flags to the
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compiler to use when building the debug versions of libstdc++.
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FLAGS is a quoted string of options, like
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</p>
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<pre>
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--enable-libstdcxx-debug-flags='-g3 -O1 -gdwarf-2'</pre>
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</dd>
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<dt><code>--enable-cxx-flags=FLAGS</code></dt>
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<dd><p>With this option, you can pass a string of -f (functionality)
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flags to the compiler to use when building libstdc++. This
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option can change the library ABI. FLAGS is a quoted string of
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options, like
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</p>
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<pre>
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--enable-cxx-flags='-fvtable-gc -fomit-frame-pointer -ansi'</pre>
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<p>
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Note that the flags don't necessarily have to all be -f flags,
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as shown, but usually those are the ones that will make sense
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for experimentation and configure-time overriding.
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</p>
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<p>The advantage of --enable-cxx-flags over setting CXXFLAGS in
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the 'make' environment is that, if files are automatically
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rebuilt, the same flags will be used when compiling those files
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as well, so that everything matches.
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</p>
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<p>Fun flags to try might include combinations of
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</p>
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<pre>
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-fstrict-aliasing
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-fno-exceptions
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-ffunction-sections
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-fvtable-gc</pre>
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<p>and opposite forms (-fno-) of the same. Tell us (the libstdc++
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mailing list) if you discover more!
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</p>
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</dd>
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<dt><code>--enable-c99 </code></dt>
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<dd><p>The "long long" type was introduced in C99, along
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with many other functions for wide characters, and math
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classification macros, etc. If enabled, all C99 functions not
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specified by the C++ standard will be put into <code>namespace
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__gnu_cxx</code>, and then all these names will
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be injected into namespace std, so that C99 functions can be
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used "as if" they were in the C++ standard (as they
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will eventually be in some future revision of the standard,
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without a doubt). By default, C99 support is on, assuming the
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configure probes find all the necessary functions and bits
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necessary. This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-wchar_t </code>[default]</dt>
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<dd><p>Template specializations for the "wchar_t" type are
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required for wide character conversion support. Disabling
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wide character specializations may be expedient for initial
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porting efforts, but builds only a subset of what is required by
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ISO, and is not recommended. By default, this option is on.
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This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-long-long </code></dt>
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<dd><p>The "long long" type was introduced in C99. It is
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provided as a GNU extension to C++98 in g++. This flag builds
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support for "long long" into the library (specialized
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templates and the like for iostreams). This option is on by default:
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if enabled, users will have to either use the new-style "C"
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headers by default (i.e., <cmath> not <math.h>)
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or add appropriate compile-time flags to all compile lines to
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allow "C" visibility of this feature (on GNU/Linux,
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the flag is -D_ISOC99_SOURCE, which is added automatically via
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CPLUSPLUS_CPP_SPEC's addition of _GNU_SOURCE).
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This option can change the library ABI.
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</p>
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</dd>
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<dt><code>--enable-fully-dynamic-string </code></dt>
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<dd><p>This option enables a special version of basic_string avoiding
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the optimization that allocates empty objects in static memory.
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Mostly useful together with shared memory allocators, see PR
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libstdc++/16612 for details.
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</p>
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</dd>
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<dt><code>--enable-concept-checks </code></dt>
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<dd><p>This turns on additional compile-time checks for instantiated
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library templates, in the form of specialized templates,
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<a href="19_diagnostics/howto.html#3">described here</a>. They
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can help users discover when they break the rules of the STL, before
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their programs run.
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</p>
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</dd>
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<dt><code>--enable-symvers[=style] </code></dt>
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<dd><p>In 3.1 and later, tries to turn on symbol versioning in the
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shared library (if a shared library has been requested). The
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only 'style' currently supported is 'gnu' which requires that
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a recent version of the GNU linker be in use. With no style
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given, the configure script will try to guess if the 'gnu'
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style can be used, and if so, will turn it on. Hopefully
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people will volunteer to do other 'style' options.
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</p>
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</dd>
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<dt><code>--enable-libstdcxx-pch </code></dt>
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|
<dd><p>In 3.4 and later, tries to turn on the generation of
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stdc++.h.gch, a pre-compiled file including all the standard
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|
|
C++ includes. If enabled (as by default), and the compiler
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seems capable of passing the simple sanity checks thrown at
|
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|
it, try to build stdc++.h.gch as part of the make process.
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In addition, this generated file is used later on (by appending <code>
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--include bits/stdc++.h </code> to CXXFLAGS) when running the
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| 298 |
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testsuite.
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</p>
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</dd>
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<dt><code>--disable-hosted-libstdcxx </code></dt>
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<dd><p>By default, a complete <em>hosted</em> C++ library is built. The
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C++ Standard also describes a <em>freestanding</em> environment,
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in which only a minimal set of headers are provided. This option
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builds such an environment.
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</p>
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</dd>
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</dl>
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<p>Return <a href="#top">to the top of the page</a> or
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<a href="http://gcc.gnu.org/libstdc++/">to the libstdc++ homepage</a>.
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<hr />
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<p class="fineprint"><em>
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See <a href="17_intro/license.html">license.html</a> for copying conditions.
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Comments and suggestions are welcome, and may be sent to
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<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
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</em></p>
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