Cmake-Linker error when linking Cmake-Library in subdirectory

edit

Hello, I'm trying to link an existing (selfwritten cmake lib) with my ros node, but when I try to link it, I get

undefined reference to ros::init(int&, char**, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned int)

and many others (all undefined references, all in the ros namespace)

My Cmake file:

cmake_minimum_required(VERSION 3.0.2)
project(ros_motor)
add_compile_options(-std=c++11)
find_package(catkin REQUIRED COMPONENTS
  can_msgs
  roscpp
  socketcan_interface
)

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES ros_motor
#  CATKIN_DEPENDS can_msgs roscpp socketcan_interface
#  DEPENDS system_lib
)
add_subdirectory(lib/motor/)
include_directories(

  ${catkin_INCLUDE_DIRS}
)
add_executable(motor_node src/motor_node.cpp)
target_link_libraries(motor_node motor ${catkin_PACKAGES})

I don't know where my issue is, else I wouldn't post here :)

Edit: My code of motor_node.cpp:

#include <ros/ros.h>
#include <can_msgs/Frame.h>
#include "motor.h"

int main(int argc, char **argv) {
    ros::init(argc, argv, "motor_node");
    ros::NodeHandle nh;
    ros::Rate r(10);
    auto motor_command_pub = nh.advertise<can_msgs::Frame>("/can/send", 10, false);
    int max = 30;
    int min = 10;
    int current = 10;
    int increment = 1;
    bool rev = false;
    auto ccmode = CurrentControl(0xDF);
    while(!ros::isShuttingDown()) {
        ccmode.setCurrent(current);
        auto frame = ccmode.getMessage();
        can_msgs::Frame ros_frame;
        ros_frame.dlc = 8;
        ros_frame.id = frame->can_id;
        boost::array<uint8_t, 8> data;
        auto c_frame = ros_frame.data.c_array();
        c_frame = frame->data;
        motor_command_pub.publish(ros_frame);
        if(current < max && !rev) {
            current += increment;
        } else if(current == max){
            rev = true;
            current -= increment;
        } else if(current > min){
            current -= increment;
        } else {
            rev = false;
            current += increment;
        }
        r.sleep();
    }
}

Motor.h of the library: #ifndef _MOTOR_H_ #define _MOTOR_H_

#include "can_frame.h"
#include "motor_const.h"
#include "Send/MessageBuilder.h"
//#include "Recv/MultipleControllerParser.h"

#endif

Send/MessageBuilder.h:

class MessageBuilder {
    protected:
        uint8_t data[8];
        uint8_t can_address;
    public:
        MessageBuilder(uint8_t address);
        MessageBuilder();
        can_frame* getMessage();
};

class ScanMessage : public MessageBuilder {
    public:
        ScanMessage();
};

class PingMessage : public MessageBuilder {
    public:
        PingMessage(uint8_t address);
};

class CurrentControl : public MessageBuilder {
    public:
        CurrentControl(uint8_t address);
        void setCurrent(int32_t current);
};

Can't provide more :)