Finding required packages

Recommended method

If you want to specify a dependency on several catkin components simultaneously, use find_package(catkin [XX.YY] REQUIRED COMPONENTS comp1 comp2), e.g.:

find_package(catkin REQUIRED COMPONENTS
             cpp_common rostime roscpp_traits
             roscpp_serialization sensor_msgs)
include_directories(${catkin_INCLUDE_DIRS})

add_executable(myexec ...)
target_link_libraries(${catkin_LIBRARIES})

You can also reference the variables of each component individually:

target_link_libraries(${rostime_LIBRARIES})

See the CMake documentation for find_package() for more details. Your CMAKE_PREFIX_PATH will need to point to a catkin installation.

find_package() config mode

CMake’s find_package is the preferred method for packages to communicate to CMake (and thereby to catkin) the libraries, include directories and such that packages should use.

There are a couple of modes of operation of find_package (see the CMake documentation), “module” mode and “config” mode. “module” mode is the one that uses CMake scripts named Find****.cmake. “config” mode is the preferred mode, and it works differently.

One reason we find the ‘config mode’ superior is that is supports multiple simultaneous installed versions of packages.

For a package t, ‘config mode’ consists of two CMake files, both of which are installed somewhere on CMake’s CMAKE_PREFIX_PATH. The first is ‘tConfig-version.cmake’. We find the most succinct form to be like this:

set(PACKAGE_VERSION_EXACT False)
set(PACKAGE_VERSION_COMPATIBLE False)
if("${PACKAGE_FIND_VERSION}" STREQUAL "")
  set(PACKAGE_VERSION_COMPATIBLE TRUE)
  return()
endif()

if("${PACKAGE_FIND_VERSION}" VERSION_EQUAL "9.9.9")
  set(PACKAGE_VERSION_EXACT True)
  set(PACKAGE_VERSION_COMPATIBLE True)
endif()

if("${PACKAGE_FIND_VERSION}" VERSION_LESS "9.9.9")
  set(PACKAGE_VERSION_COMPATIBLE True)
endif()

where 9.9.9 is replaced by the numeric version of the package. The second file, tConfig.cmake, tells the client what the assorted includes/libs are for the package by setting variables t_INCLUDE_DIRS, t_LIBRARIES, t_LIBRARY_DIRS and so forth. The user passes these values to CMake’s include_directories() and target_link_libraries(). Since the libraries contains absolute paths link_directories() is not necessary.