On Mon, Mar 4, 2024, at 12:17 AM, Peter Johansson wrote: > This is with autoconf 2.72 and GCC 9.4.0. > I try to configure a project with > > ./configure 'CXX=c++ -std=c++2a' > > but the configure seems to dislike that because it outputs > > checking whether the compiler supports GNU C++... yes > checking whether c++ -std=c++2a accepts -g... yes > checking for c++ -std=c++2a option to enable C++11 features... -std=gnu++11 > checking dependency style of c++ -std=c++2a -std=gnu++11... gcc3 > > So it decides to add -std=gnu++11. Yeah, the logic for selecting a version of the C++ standard is inflexible at the moment. It always tries to force the highest standard that it already knows about -- and right now that's C++ 2011, no higher. (At the time 2.72 was released, the 202x C and C++ standards were still in flux so we elected not to add support for them.) Making it more flexible -- specifically, allowing the project to declare which version of the standard they want to use -- is tracked as <https://savannah.gnu.org/support/index.php?110286>. Also, what we currently have assumes that code that's valid in C++ XXXX will _remain_ valid in C++ YYYY, where YYYY > XXXX. That used to be reliably true but the 202x standard drafts broke it. That's why the test program threw the error you quoted... > conftest.cpp: In function 'int main(int, char**)': > conftest.cpp:199:22: error: invalid conversion from 'const char8_t*' to > 'const char*' [-fpermissive] > 199 | char const *utf8 = u8"UTF-8 string \u2500"; Fixing these things is a high priority for Autoconf 2.73 but nobody currently has time to work on it. If you have time, we would appreciate your working on it -- even just a rough draft of revised test programs would be helpful. zw
