Mosquitto with ROS Jade undefined reference

Question

I am currently using ROS Jade in Ubuntu 14.04 and am trying to create a MQTT Publisher to my Mosquitto software. However, I am unable to build it properly via catkin_make. In my main cpp code, I have included the "mosquitto.h" file. Apologies that I am unable to post my cpp file as it is for work purposes.

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.3)

find_package(catkin REQUIRED COMPONENTS
roscpp
rospy
std_msgs
)

catkin_package(
INCLUDE_DIRS include
LIBRARIES mqtt 
CATKIN_DEPENDS roscpp std_msgs
DEPENDS system_lib
)

set(MOSQ_LIB_LOCATIONS
/usr/lib
)

set(INCLUDE_HEADER_FILES
src/mosquitto.h
#include/lib/cpp/mosquittopp.h
)

include_directories(
${catkin_INCLUDE_DIRS}
${mosquitto_INCLUDE_DIRS}
/home/catkin_ws/src/mqtt/include/lib
/home/catkin_ws/src/mqtt/include/lib/cpp
)

add_executable(mqtt src/mqtt.transmit.cpp ${INCLUDE_HEADER_FILES} ${MOSQ_LIB_LOCATIONS})
target_link_libraries(mqtt ${catkin_LIBRARIES})

Error

mqtt.transmit.cpp:(.text+0x1f8): undefined reference to `mosquitto_lib_init'
mqtt.transmit.cpp:(.text+0x210): undefined reference to `mosquitto_new'
mqtt.transmit.cpp:(.text+0x237): undefined reference to `mosquitto_username_pw_set'
mqtt.transmit.cpp:(.text+0x259): undefined reference to `mosquitto_connect'
mqtt.transmit.cpp:(.text+0x285): undefined reference to `mosquitto_loop_start'
mqtt.transmit.cpp:(.text+0x2bc): undefined reference to `mosquitto_publish'
mqtt.transmit.cpp:(.text+0x2d0): undefined reference to `mosquitto_loop_stop'
mqtt.transmit.cpp:(.text+0x2df): undefined reference to `mosquitto_disconnect'
mqtt.transmit.cpp:(.text+0x2ee): undefined reference to `mosquitto_destroy'
mqtt.transmit.cpp:(.text+0x2f3): undefined reference to `mosquitto_lib_cleanup'
collect2: error: ld returned 1 exit status

I initially thought that there was an error reading the header file which I included, but if that was the case, the "no such file directory" error would occur. The functions that were in the "undefined references" are located in the header file which I included, not sure why it is still undefined. Would appreciate the guidance to get rid of the undefined reference.

Thanks so much!

[EDIT] I got the MQTT Publishing cpp code from the following site, you have to scroll to the bottom. Thanks! Mosquitto software is working fine. https://robomq.readthedocs.io/en/latest/MQTT/

Answer 1

Solved. When using Mosquitto, I had to link the client library in my CMakeList. Basically the libmosquitto.so file, which is the client library.

I added the following to my cmake list:

set(Mosquitto_libs
  /usr/lib/x86_64-linux-gnu/libmosquitto.so
  /usr/lib/x86_64-linux-gnu/libmosquitto.so.1
)
target_link_libraries(mqtt_pub_node ${catkin_LIBRARIES} ${Mosquitto_libs})

Answer 2

In this case it's the linker that cannot find the object files that contain the function names displayed in the error output. Unless you changed this CMake file, I would guess that the necessary object files are not in your /usr/lib dir which is where the linker is looking.