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17 options</A></H1>
19 <P>The latest version of this document is always available at
21 http://sources.redhat.com/libstdc++/configopts.html</A>.
22 </P>
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29 <P>Here are some of the non-obvious options to libstdc++'s configure.
30 Keep in mind that
31 <!-- This SECnn should be the "Choosing Package Options" section. -->
33 all have opposite forms as well</A>
34 (enable/disable and with/without). The defaults are for the latest
35 snapshot, 2.90.8.
36 <P>
37 The canonical way to find out the configure options that are
38 available for a given set of libstdc++ sources is to go to the
41 <DL>
43 <DD><P>This is part of the generic multilib support for building
44 cross compilers. As such, targets like "powerpc-elf" will
45 have libstdc++ built many different ways: "-msoft-float" and
46 not, etc. A different libstdc++ will be built for each of the
47 different multilib versions. This option is on by default.
48 </P>
51 <DD><P>The configure script will automatically detect the highest level
52 of optimization that the compiler in use can use (certain
54 this is fixed in later versions of the compiler). This --enable
55 flag will disable all optimizations and instruct the compiler to
56 emit as much extra debugging information as it can, for use
57 inside GDB.
58 </P>
62 (described next).
63 </P>
66 <DD><P>Select a target-specific I/O package. As of libstdc++-v3
67 snapshot 2.90.8, the choices are 'libio' to specify the GNU
68 I/O package (from
70 GNU C library), or 'wince' to specify the Microsoft Windows CE
71 library. Eventually a generic cstdio interface will be added
72 so that people who want to use libstdc++-v3 with say, the Palm
73 Pilot, will be able to use libstdc++-v3 without libio.
74 </P>
78 provided as a GNU extension to C++98 in g++. This flag builds
80 templates and the like).
81 </P>
85 backwards compatibility. It can be turned on with the
87 snapshot 2.90.8, that flag is passed to g++ when building the
88 library. (In g++ 2.96 and later, this flag is on by default if
89 libstdc++-v3 is used.) The --disable variant will put all std::
90 symbols into the global namespace.
91 </P>
94 <DD><P>This turns on the code to construct shadowed C headers. Very
95 experimental as of this writing.
96 </P>
100 (described next).
101 </P>
105 the choices are:
106 'yes' for some kind of default (hmmmmm);
107 'decosf1', 'irix', 'mach', 'os2', 'posix'/'pthreads'
108 (same thing),
109 'solaris', 'win32', 'dce', or 'vxworks' to select the
110 corresponding interface;
111 and 'single', 'no', or 'none' for the null-case,
112 single-threaded library.
113 </P>
114 <P>All of this is currently undergoing a lot of changes. As of
115 2.90.8, 'single' and 'posix' are the only implemented models.
116 </P>
119 <DD><P>This is a grueling temporary hack no matter which way you look
121 little page</A>. Note that other --enable flags will
122 interact with this one. In libstdc++-v3 snapshot 2.90.8,
123 this is enabled by default, with DIR set to
125 with libstdc++-v3 in place works transparently. Since then,
126 library sources have been merged into the compiler sources,
127 and this option has been removed.
128 </P>
131 <DD><P>With this option, you can pass a string of -f (functionality)
132 flags to the compiler to use when building libstdc++. FLAGS
133 is a quoted string of options, like
134 <PRE>
135 --enable-cxx-flags='-fsquangle -fvtable-gc -ansi'</PRE>
136 Note that the flags don't necessarily have to all be -f flags,
137 as shown, but usually those are the ones that will make sense
138 for experimentation and configure-time overriding.
139 </P>
140 <P>The advantage of --enable-cxx-flags over setting CXXFLAGS in
141 the 'make' environment is that, if libgcc is automatically
142 rebuilt, the same flags will be used when compiling those files
143 as well, so that everything matches.
144 </P>
145 <P>Fun flags to try might include combinations of
146 <PRE>
147 -fstrict-aliasing
148 -fnew-abi
149 -fnew-exceptions
150 -ffunction-sections
151 -fvtable-gc</PRE>
152 and -fno- forms of the same. Tell us (the mailing list) if
153 you discover more!
154 </P>
157 <DD><P>Certain template specializations are required for wide character
158 conversion support. This is tricky and currently changing rapidly,
159 and can cause problems on new platforms. Disabling wide character
160 specializations is useful for initial porting steps, but builds
161 only a subset of what is required by ISO.
162 </P>
163 </DL>
164 </P>
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