What's new with G++

A number of major changes appear in this release of G++. If some features mentioned below sound unfamiliar, you will probably want to look at the recently-released public review copy of the C++ Working Paper. For PostScript and PDF (Adobe Acrobat) versions, see the archive at `ftp://research.att.com/dist/stdc++/WP'. For HTML and ASCII versions, see `ftp://ftp.cygnus.com/pub/g++'. On the Web, see `http://www.cygnus.com/misc/wp-draft'.

• -fhandle-exception This is a flag to the C++ frontend. This option turns on C++ exception handling as documented in the ANSI draft standard for C++. This draft standard can be viewed at `http://www.cygnus.com/misc/'. This option adds some readonly text and readonly data space overhead necessary for the implementation of exception handling. It cannot be used with -O yet. The option -frtti can be used in conjunction with this flag to enable subtype matching on catch clauses.
• Binary incompatibility Classes that do not define the copy constructor will sometimes be passed and returned in registers. This may illuminate latent bugs in our code. This will not affect the SPARC, as the ABI specifies that structs are never passed in registers.
• Support for automatic template instantiation For this support to work, the template definition must be available at one or more use sites; as ever, G++ will not go looking in other files. Use the -frepo flag when compiling to enable; collect2 will recompile affected files as necessary toprovide all needed template instantiations. Do not use -fexternal-templates with -frepo.
• for-init-statement The scope of variables declared in the for-init-statement has been changed to conform to

  http://www.cygnus.com/misc/wp-draft/stmt.html#stmt.for
  

  Most old code will continue to compile with a warning; use -ffor-scope to disallow it or -fno-for-scope to revert to the old semantics.
• keyword typename for G++ G++ now accepts the typename keyword, though it currently has no semantics; it can be a no-op in the current template implementation. You may want to start using it in your code, however, since the pending rewrite of the template implementation to compile STL properly (perhaps for 2.8.0, perhaps not) will require you to use it as indicated by the current draft.
• Testing conditions improved The code generated for testing conditions, especially those using || and &&, is now more efficient.
• User-defined type conversion Handling of user-defined type conversion has been overhauled so that type conversion operators are now found and used properly in expressions and function calls.
• extern inline Functions declared extern inline now have the same linkage semantics as inline member functions. On supported targets, where previously these functions (and vtables, and template instantiations) would have been defined statically, they will now be defined as weak symbols so that only one out-of-line definition is used.
• collect2 collect2 now demangles linker output, and c++filt has become part of the GCC distribution.
• Class template members Specializations of class template members can now be declared.
• Synthesized methods Synthesized methods are now emitted exactly as needed; they are no longer affected by #pragma interface/implementation or the location of the vtable.
• Linking with libg++ There are two issues:
  1. Symbols referenced by the shared library that wouldn't be referenced linking with the static library. Specifically, the curses functions.
  2. Finding the shared library at run time.
  The fixes for the first are:
  1. Don't link with libg++ (if using g++, use c++ instead), OR
  2. Link with -lcurses (and possibly -ltermcap), OR
  3. Remove `/usr/progressive/lib/libg++.s*', OR
  4. Link with -static to avoid using any shared libraries
  The fixes for the second are:
  1. Add `/usr/progressive/lib' to your LD_LIBRARY_PATH environment variable, OR
  2. Use the appropriate option when linking: -rpath `/usr/progressive/lib' for DEC UNIX (OSF/1), -R `/usr/progressive/lib' for Solaris. SunOS 4 does not need such an option, nor does AIX.