https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104397
Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Status|UNCONFIRMED |WAITING Last reconfirmed| |2022-02-05 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This does not use modules though: g++ -Wall class.hpp class.cpp main.cpp -o main This just uses precompiled headers. As shown by: #pragma GCC pch_preprocess "class.hpp.gch" This means the a is defined but not used. See https://gcc.gnu.org/onlinedocs/gcc-11.2.0/gcc/C_002b_002b-Modules.html#C_002b_002b-Modules on how to use modules rather than precompiled headers.