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| <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)"> |
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| <meta name="DESCRIPTION" content="Configuration options for libstdc++-v3."> |
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| <h1 class="centered"><a name="top">Interesting <code>configure</code> |
| 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:<code> ./configure --help</code> |
| |
| <dl> |
| <dt><code>--enable-multilib </code>[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><code>--enable-debug </code> |
| <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 <code>-O2</code> |
| 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. Note this make command, executed in |
| the build directory, will do much the same thing, without the |
| configuration difference:<code>make CXXFLAGS='-g -O0' all</code> |
| </p> |
| |
| <dt><code>--enable-cstdio </code> |
| <dd><p>This is an abbreviated form of <code>'--enable-cstdio=stdio'</code> |
| (described next). |
| </p> |
| |
| <dt><code>--enable-cstdio=LIB </code> |
| <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><code>--enable-sjlj-exceptions </code> |
| <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><code>--enable-clocale </code> |
| <dd><p>This is an abbreviated form of <code>'--enable-clocale=generic'</code> |
| (described next). |
| </p> |
| |
| <dt><code>--enable-clocale=MODEL </code> |
| <dd><p>Select a target-specific underlying locale package. The |
| choices are 'ieee_1003.1' to specify an X/Open, Standard Unix |
| (IEEE Std. 1003.1-200x) model based on langinfo/iconv/catgets, |
| 'gnu' to specify a model based on functionality from the GNU C |
| library (langinfo/iconv/gettext) (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><code>--enable-c99 </code> |
| <dd><p>The "long long" type was introduced in C99, along |
| with many 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 <code>namespace |
| __gnu_cxx</code>, and then all these names 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><code>--enable-long-long </code> |
| <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><code>--enable-cheaders=OPTION </code> |
| <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><code>--enable-threads </code> |
| <dd><p>This is an abbreviated form of <code>'--enable-threads=yes'</code> |
| (described next). |
| </p> |
| |
| <dt><code>--enable-threads=LIB </code> |
| <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><code>--enable-version-specific-runtime-libs </code> |
| <dd><p>Specify that run-time libraries should be installed in the |
| compiler-specific subdirectory (i.e., |
| <code>${libdir}/gcc-lib/${target_alias}/${gcc_version}</code>) |
| instead of <code>${libdir}</code>. 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 |
| <code>${libdir}/gcc-lib/${target_alias}/${gcc_version}/include/g++</code>, |
| unless you also specify |
| <code>--with-gxx-include-dir=<em>dirname</em></code> during configuration. |
| </p> |
| |
| <dt><code>--with-gxx-include-dir=<include-files dir></code> |
| <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><code>--enable-cxx-flags=FLAGS</code> |
| <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 libstdc++ |
| mailing list) if you discover more! |
| </p> |
| |
| <dt><code>--enable-c-mbchar </code>[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. By default, this option is on. |
| </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 libstdc++ homepage</a>. |
| </p> |
| |
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| See <a href="17_intro/license.html">license.html</a> for copying conditions. |
| Comments and suggestions are welcome, and may be sent to |
| <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>. |
| </em></p> |
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