gcc -pthread  -Wall -Wextra -Werror=implicit-function-declaration unistd/getlogin_r.c -o unistd/getlogin_r -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt -lxnet -lsocket -latomic
unistd/getlogin_r.c: In function 'main':
unistd/getlogin_r.c:16:22: error: initialization of 'int' from 'char *' makes integer from pointer without a cast [-Wint-conversion]
   16 |         int errnum = getlogin_r(buf, sizeof(buf));
      |                      ^~~~~~~~~~