Hi Jonathan, Thanks for the answer! I also found the GCC ABI compatibility wiki page you mentioned, that's why I had concerns. At least these seem to be real issues for us: * `vector::data()`'s return type changes from `pointer` to `_Tp*` [gcc-4.6 - ...] * `std::operator-(reverse_iterator)` and `std::operator-(__normal_iterator)` [gcc-4.4 - ...] * `istreambuf_iterator::reference` changes from `_CharT&` to `_CharT` [gcc-4.7 - ...] This also, but at least it would cause compilation error: * Types with node allocators, like `deque` and lists, maps and sets [... - gcc-5] Based on the wiki page, I'm not sure how we could pinpoint the root cause if any of the above issues would be triggered in our program, especially if they would manifest in some runtime fault. On the other hand, they all seem to be very "esoteric" issues, and luckily most of our 3PP libraries focus on using as few C++ language features as possible. I hope this "mixed C++ versions" approach will turn out to be usable. Thanks, Tamas 2016-08-22 15:31 GMT+02:00 Jonathan Wakely <jwakely.gcc@xxxxxxxxx>: > On 22 August 2016 at 14:15, Tamás Kiss wrote: >> Hi, >> >> I'd like to ask some questions about codebase migration to C++11. In >> the company I work, we have a large C++ codebase, currently C++98. We >> recently upgraded GCC to 4.8.3, so at last using C++11 became a >> possibility. Our product is built on-, and runs on x86_64 Linux >> platform only, so no cross-platform considerations are needed. We also >> make use of some third party C++ libraries, that are also C++98. We >> build everything from sources (including the 3PPs), so recompilation >> is not an issue, and we always deploy all of our built code together >> (i.e. no partial upgrades), so backwards compatibility between our >> components is also not a problem. >> >> We plan to recompile our own codebase with the -std=c++11 flag, and if >> there are any problems, we can rewrite the necessary code parts. And >> here comes my question at last :) Do we need to use the -std=c++11 >> flag also while recompiling the 3PP libraries, or is it enough to use >> the same build environment with the same GCC version as used for our >> own code? Or more simply put: can we use C++11 code and C++98 >> libraries together, given that they are compiled with the same >> compiler on the same environment, just with different language version >> flags? > > Yes. > > There are some rare corner cases that can cause problems, see > https://gcc.gnu.org/wiki/Cxx11AbiCompatibility > > With GCC 4.8.3 you should be OK. > > Be aware that the ABI for the new C++11 components was not stable > until GCC 5.1, so if you upgrade to GCC 4.9.x you'll need to rebuild > everything again, and similarly if you upgrade to GCC 5.x > > Since GCC 5.1 the C++11 support is stable and provides the same level > of ABI compatibility between releases as has long been available for > C++98 support. > > See https://gcc.gnu.org/gcc-6/porting_to.html for some common problems > encountered when switching to C++11.
