Sometimes it’s convenient to build multiple nodes into a single package, if multiple nodes share libraries. In this post we’ll discuss some use cases for including multiple packages in the CMakeLists.txt file.

Build two libraries without executables

Here’s an example where we build a library called alpha and a separate library called beta, which uses the library alpha.

CMakeLists.txt

# alpha
add_library(alpha
      src/Alpha.cpp
)

target_link_libraries(alpha
      ${catkin_LIBRARIES}
)

# beta
add_library(beta
      src/Beta.cpp
)

target_link_libraries(beta
      alpha
      ${catkin_LIBRARIES}
)

Build a third library with an executable

This example builds a library omega which has an executable associated with it, and also depends on alpha.

CMakeLists.txt

# omega
add_library(omega
      src/Omega.cpp
)

add_executable(omega_node_executable
      src/omega_main.cpp
      src/Omega.cpp
)

target_link_libraries(omega_node_executable
			alpha
      ${catkin_LIBRARIES}
)

So far, this will build alpha, beta, and omega into the project namespace ${PROJECT_NAME}. Therefore, if you go into .../devel/lib/${PROJECT_NAME}, you should see them there. If you wish to build, say alpha, directly under the ${PROJECT_NAME}, add this:

CMakeLists.txt

set_target_properties(alpha
  PROPERTIES OUTPUT_NAME ${PROJECT_NAME}
)

This will build alpha directly into ${PROJECT_NAME}.

Export libraries to be used by other packages

To export libraries to be used by other packages, first add libraries to the catkin_package specification, and then install the targets:

CMakeLists.txt

catkin_package(
      INCLUDE_DIRS include
      LIBRARIES ${PROJECT_NAME} alpha beta
      CATKIN_DEPENDS
      DEPENDS
)
...

install(TARGETS alpha beta
      ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
      LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
      RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)