On 24 March 2016 at 12:20, Jeffrey Walton <noloader@xxxxxxxxx> wrote: > On Thu, Mar 24, 2016 at 8:10 AM, Jonathan Wakely <jwakely.gcc@xxxxxxxxx> wrote: >> On 24 March 2016 at 11:55, Jeffrey Walton wrote: >>> In the test program below, why does -Wabi-tag trigger a warning with >>> the std::string when using -std=c++03? >> >> "Although the changes were made for C++11 conformance, the choice of >> ABI to use is independent of the -std option used to compile your >> code, i.e. for a given GCC build the default value of the >> _GLIBCXX_USE_CXX11_ABI macro is the same for all dialects. This >> ensures that the -std does not change the ABI, so that it is >> straightforward to link C++03 and C++11 code together. " >> >> https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html > > Thanks. I recall reading that a couple of days ago. I still don't > quite understand what it means. I'm obviously missing something. > > I guess my knowledge gap is due to _GLIBCXX_USE_CXX11_ABI should apply > to C++11 and above to comply with the newer C++ rules, wrote-on-copy > strings, etc. I don't understand how it effects C++03 and below since > the rules that required the change don't apply. The new std::string and std::list are also valid implementations for C++03. Try reading this bit again: "This ensures that the -std does not change the ABI, so that it is straightforward to link C++03 and C++11 code together."
