gcc -pthread -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations sys_socket/SO_PROTOCOL.c -o sys_socket/SO_PROTOCOL -D_POSIX_C_SOURCE=202405L -lm -lpthread -lrt -lxnet -lsocket -latomic sys_socket/SO_PROTOCOL.c:2:17: error: ‘SO_PROTOCOL’ undeclared here (not in a function); did you mean ‘SO_PROTOTYPE’? 2 | int const foo = SO_PROTOCOL; | ^~~~~~~~~~~ | SO_PROTOTYPE