https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86138
--- Comment #3 from Christian Franke <franke at computer dot org> --- (In reply to Jonathan Wakely from comment #1) > Why is the one in the DLL not compatible? I don't know. > The extern templates are disabled because std::basic_string has additional > member functions in C++17 mode, and they're not instantiated in the library. > By disabling the explicit instantiation declarations the compiler will emit > definitions for the C++17-only member functions. This has no effect due to the bogus specialization in basic_string.h (see patch below). > As requested at https://gcc.gnu.org/bugs testcases need to be provided here, > not as URLs. Sorry. New testcase below: $ uname -srvmo CYGWIN_NT-10.0 2.10.0(0.325/5/3) 2018-02-02 15:16 x86_64 Cygwin $ g++ --version g++ (GCC) 7.3.0 $ cygcheck -f /bin/cygstdc++-6.dll libstdc++6-7.3.0-2 $ cat getlinetest.cpp #include <sstream> int main() { std::string line; std::istringstream stream("*"); std::getline(stream, line, '\n'); return (int)line.c_str()[0]; } $ g++ -o getlinetest getlinetest.cpp && ./getlinetest; echo $? 42 $ g++ -std=c++17 -o getlinetest getlinetest.cpp && ./getlinetest; echo $? Aborted (core dumped) 134 $ g++ -std=c++17 -static -o getlinetest getlinetest.cpp && ./getlinetest;\ echo $? 42 Interestingly the statically linked version works. Is there possibly some template function called by getline() which is not C++17 compatible? In the static case the new version of this function from getline.o is used instead of the old one in the lib*.a file. Possible fix (char only, should also be done for wchar_t): $ cat basic_string.h.patch --- basic_string.h.orig 2018-05-03 06:22:46.000000000 +0200 +++ basic_string.h 2018-06-19 07:49:50.190322000 +0200 @@ -6329,11 +6329,6 @@ { return std::getline(__is, __str); } #endif - template<> - basic_istream<char>& - getline(basic_istream<char>& __in, basic_string<char>& __str, - char __delim); - #ifdef _GLIBCXX_USE_WCHAR_T template<> basic_istream<wchar_t>& $ (cd /usr/lib/gcc/x86_64-pc-cygwin/7.3.0/include/c++/bits && patch) \ < basic_string.h.patch patching file basic_string.h $ g++ -std=c++17 -o getlinetest getlinetest.cpp && ./getlinetest; echo $? 42
