On Mon, Oct 10, 2011 at 5:25 PM, Joe Buck <joe.b...@synopsys.com> wrote: > On Fri, Oct 07, 2011 at 07:35:17PM -0700, Gabriel Dos Reis wrote: >> C++11 is essentially binary incompatible with C++98. > > Only partially. The layout for user-defined classes is the same, and
PODness has changed from C++98. > code sequences for calls that don't include new features like rvalue > references is the same. Some very important classes from the standard > library are different, and that creates an incompatibility. It is not just class layout. It is also function signatures. > >> The best thing people should do is to take it seriously that that they should >> not attempt to mix or play loose. > > Unfortunately, distros aren't going to start shipping two versions of > every C++ library, so people are going to have to solve the problem that > you are saying should not be solved, or at least determine which cases > are problems and which aren't. If common libraries are all c++98-only > this will slow the adoption of c++11: forcing a flag day when this is not > necessary is probably not the right thing to do. By no means am I preventing anybody from solving that problem if they believe that is how their time is best spent. I am offering only a realistic assessment. When distros deam g++ support for C++11 sufficiently well advanced that they feel adventurous enough to officially support the experimental support, then I am confident they will do the responsible thing: offer two sets of libraries, as they did in the past when we moved to GCC3. > > I wrote: >> Eventually there would need to be one libstdc++ that programs link against >> and >> run whether they use c++98 or c++11. I would expect there to be restrictions, >> but it's a problem that eventually needs to be tackled. > > Gaby writes: > >> My opinion is that it would an exercise in futility, frustration, and >> possibly deception to try to make people believe that there are sets of >> simple rules they can follow to mix their C++98 binaries with fully >> compatible C++11 library. They would have to recompile the source code. > > They will need to build their code with the same compiler, yes, and it > won't be binary-compatible with older versions. But as of today, the > templates in libstdc++ expand differently depending on language mode, so > the library is already providing both sets of interfaces. For the record, I am not endorsing this as a recommendation for those interested in C++11 -- I am already stated my recommendation. > > A bump to libstdc++ major version number could be made that ensures, for > example, that std::string satisfies the requirements of both languages. > It's also possible that the code in the standard library uses c++11 features > internally even when the user has specified c++98 (to get move semantics, > for example). > >
