what is causing this error?
savannapan@Savannas-MacBook-Pro a4 % make
gcc -DPORT=\59208 -g -std=gnu99 -Wall -Werror  -o friend_server friend_server.c
Undefined symbols for architecture x86_64:
  "_accept_connection", referenced from:
      _main in friend_server-0cc6cb.o
  "_init_server_addr", referenced from:
      _main in friend_server-0cc6cb.o
  "_set_up_server_socket", referenced from:
      _main in friend_server-0cc6cb.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [friend_server] Error 1