clang -O2 -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations unistd/setregid.c -o unistd/setregid -D_POSIX_C_SOURCE=202405L -lm -lintl unistd/setregid.c:11:28: error: use of undeclared identifier 'setregid'; did you mean 'setegid'? int (*foo)(gid_t, gid_t) = setregid; ^~~~~~~~ setegid /usr/include/unistd.h:179:6: note: 'setegid' declared here int setegid(gid_t); ^ unistd/setregid.c:11:7: error: incompatible pointer types initializing 'int (*)(__gid_t, __gid_t)' with an expression of type 'int (__gid_t)' [-Werror,-Wincompatible-pointer-types] int (*foo)(gid_t, gid_t) = setregid; ^ ~~~~~~~~ 2 errors generated.