How do I properly link my libraries in my project using CMake?

Question

I'm currently learning CMake and I'm trying to create my first test project. I'm able to get a simple project up and running in visual studio via CMake. However, I'm having trouble trying to add a library. I've read some guides and things but I keep getting errors. Basically, I'm trying to link SDL libraries (a game programming library) in my sample project. I've placed these libraries in a top level, 'ThirdParty' folder. Here is what my CmakeLists.txt file looks like in my top level directory:

cmake_minimum_required(VERSION 2.8.11)

project(Hello)

#Find necessary header files
find_path(SDL_INCLUDE_DIR SDL.h HINTS ${CMAKE_SOURCE_DIR}/ThirdParty/SDL2/include/)

#Find necessary library files
find_library(SDL_LIB_DIR SDL2 HINTS ${CMAKE_SOURCE_DIR}/ThirdParty/SDL2/lib/x86)
find_library(SDLMAIN_LIB_DIR SDLmain HINTS ${CMAKE_SOURCE_DIR}/ThirdParty/SDL2/lib/x86)

#Add/Link files to project
include_directories(${SDL_INCLUDE_DIR})
target_link_libraries(Test PUBLIC ${SDL_LIB_DIR})
target_link_libraries(Test PUBLIC ${SDLMAIN_LIB_DIR})



add_executable(Test "${CMAKE_SOURCE_DIR}/Source/Main.cpp")

I'm not 100 percent sure of the HINTS parameter, but I saw it used on another thread. Anyway, here's the error I keep getting:

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
SDLMAIN_LIB_DIR
    linked by target "Test" in directory C:/Users/Jason/Desktop/Test

What am I doing wrong and how do I properly link libraries in CMake?

Answer 1

1. In cmake, you first create the executable, and then you link it to a library
2. You have to understand how finding libraries and packages works in CMake. Typically the way it works is that you use find_library or find_package , and then cmake will set some variables that you can use to link to/use the library.

I'm not familiar with SDL, but by googling a little bit about it, I would say this is how it should look like:

find_file(SDL2_INCLUDE_DIR NAME SDL.h HINTS SDL2)
find_library(SDL2_LIBRARY NAME SDL2)
add_executable(MyExec main.cpp)
target_include_directories(MyExec ${SDL2_INCLUDE_DIR})
target_link_libraries(MyExec ${SDL2_LIBRARY})

That find_library will set the variables SDL2_INCLUDE_DIR and SDL2_LIBRARY , which you can use to link to SDL and add its includes to your project.

Answer 2

I'm trying to do the same, but when I try to use my bookstore it doesn't recognize it.

catkin_package(
  INCLUDE_DIRS include ${EXTERNAL_INCLUDE_DIRS}
  LIBRARIES ${PROJECT_NAME}
  CATKIN_DEPENDS message_runtime roscpp actionlib
  DEPENDS
)

## Setup include dirs
include_directories(include ${catkin_INCLUDE_DIRS} ${Boost_INCLUDE_DIRS})
include_directories(SYSTEM ${EIGEN3_INCLUDE_DIRS})

include_directories(
  SYSTEM
  ${EXTERNAL_INCLUDE_DIRS}
  ${catkin_INCLUDE_DIRS}
)

# Trajectory planners

add_library(${PROJECT_NAME}_planners
  src/PRM_planner.cpp
 )

target_link_libraries(${PROJECT_NAME}_planners
  ${catkin_LIBRARIES}
  ${RL_LIBRARIES}
)


add_executable(trajectory_planner src/trajectory_planner.cpp)
target_link_libraries(trajectory_planner
  ${PROJECT_NAME}_planners
  ${catkin_LIBRARIES}
  ${RL_LIBRARIES}
)

In my file trajectory_planner.cpp:

#include "trajectory/prm_planner.h"


int main()
{
    prm_planner::plan();
    return 0;
}

But I have this error:

CMakeFiles/trajectory_planner.dir/src/trajectory_planner.cpp.o: In function `main':
trajectory_planner.cpp:(.text+0x5): undefined reference to `prm_planner::plan()'
collect2: error: ld returned 1 exit status
toolbox_ur3/CMakeFiles/trajectory_planner.dir/build.make:391: recipe for target '/home/euroage/catkin_ws/devel/lib/toolbox_ur3/trajectory_planner' failed
make[2]: *** [/home/euroage/catkin_ws/devel/lib/toolbox_ur3/trajectory_planner] Error 1
CMakeFiles/Makefile2:15231: recipe for target 'toolbox_ur3/CMakeFiles/trajectory_planner.dir/all' failed
make[1]: *** [toolbox_ur3/CMakeFiles/trajectory_planner.dir/all] Error 2
Makefile:140: recipe for target 'all' failed
make: *** [all] Error 2