Hello Thank you for directing me to those options.
Setting _XOPEN_SOURCE to 500 or higher seems to restore the expected functionality of attrset in ncurses for colour. _XOPEN_SOURCE is a feature test macro, so it just determines that some functionality from X/Open is used (X/OPEN 5 for _XOPEN_SOURCE 500, X/OPEN 6 for _XOPEN_SOURCE 600, etc.). The program that is being compiled can have its own tests for functionality that it needs. I can add "#define _XOPEN_SOURCE 500" to the beginning of test.c from my previous email to make it work as it should when built with guix. So, this is something, the program could normally figure out itself without relying on curses being implemented in a specific way. There is a section on alternate configurations of ncurses in its manual [1] noting that it may be necessary for some functionality of ncurses to specify _XOPEN_SOURCE up to 600 for programs compiled against ncurses when the latter was built with --enable-widec. Since this option was chosen for ncurses in guix, it is fair enough that some functionality may need _XOPEN_SOURCE 600, even if I am not sure how my case is related to wide character support or what functionality from X/Open is used. [1]: https://invisible-island.net/ncurses/man/ncurses.3x.html#h2-ALTERNATE-CONFIGURATIONS I believe that the above is enough to close this issue. Roman
