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compat.texi: Add info about C++ libraries. 

2002-10-11  Janis Johnson  <janis187@us.ibm.com>

	* doc/compat.texi: Add info about C++ libraries.

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@ -1,3 +1,7 @@
2002-10-11 Janis Johnson <janis187@us.ibm.com>
* doc/compat.texi: Add info about C++ libraries.
2002-10-11 Richard Henderson <rth@redhat.com>
PR opt/8165

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gcc/doc/compat.texi
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@ -113,3 +113,44 @@ interpretations of the C++ ABI by different vendors, bugs in the ABI, or
bugs in the implementation of the ABI in different compilers.
GCC's @code{-Wabi} switch warns when G++ generates code that is
probably not compatible with the C++ ABI@.
The C++ library used with a C++ compiler includes the Standard C++
Library, with functionality defined in the C++ Standard, plus language
runtime support. The runtime support is included in a C++ ABI, but there
is no formal ABI for the Standard C++ Library. Two implementations
of that library are interoperable if one follows the de-facto ABI of the
other and if they are both built with the same compiler, or with compilers
that conform to the same ABI for C++ compiler and runtime support.
When G++ and another C++ compiler conform to the same C++ ABI, but the
implementations of the Standard C++ Library that they normally use do not
follow the same ABI for the Standard C++ Library, object files built with
those compilers can be used in the same program only if they use the same
C++ library. This requires specifying the location of the C++ library
header files when invoking the compiler whose usual library is not being
used. The location of GCC's C++ header files depends on how the GCC
build was configured, but can be seen by using the G++ @option{-v} option.
With default configuration options for G++ 3.3 the compile line for a
different C++ compiler needs to include
@example
-I@var{gcc_install_directory}/include/c++/3.3
@end example
Similarly, compiling code with G++ that must use a C++ library other
than the GNU C++ library requires specifying the location of the header
files for that other library.
The most straightforward way to link a program to use a particular
C++ library is to use a C++ driver that specifies that C++ library by
default. The @command{g++} driver, for example, tells the linker where
to find GCC's C++ library (@file{libstdc++}) plus the other libraries
and startup files it needs, in the proper order.
If a program must use a different C++ library and it's not possible
to do the final link using a C++ driver that uses that library by default,
it is necessary to tell @command{g++} the location and name of that
library. It might also be necessary to specify different startup files
and other runtime support libraries, and to suppress the use of GCC's
support libraries with one or more of the options @option{-nostdlib},
@option{-nostartfiles}, and @option{-nodefaultlibs}.