Undefined symbols for architecture x86_64

[innerNULL]

REALLY needs help with this 'Undefined symbols for architecture x86_64:' error T T

Here is my codes

#include "oatpp-websocket/WebSocket.hpp"
#include "oatpp-websocket/Connector.hpp"

#include "oatpp/network/tcp/client/ConnectionProvider.hpp"

#include <thread>

int main(int argc, char **argv) {
  //auto connectionProvider = oatpp::network::tcp::client::ConnectionProvider::createShared({"echo.websocket.org", 80});
  //const std::shared_ptr<oatpp::websocket::WebSocket> websocket;
  oatpp::base::Environment::init();
  return 0;
}

And here is my compile error:

[ 50%] Building CXX object CMakeFiles/demo.dir/demo.cpp.o
[100%] Linking CXX executable demo
Undefined symbols for architecture x86_64:
  "oatpp::base::Environment::init()", referenced from:
      _main in demo.cpp.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[2]: *** [demo] Error 1
make[1]: *** [CMakeFiles/demo.dir/all] Error 2
make: *** [all] Error 2

[innerNULL]

My fault, forgot link oatpp lib.