Internals of the generated find_package() infrastructure¶
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 ‘t-config-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("${PACKAGE_FIND_VERSION}" VERSION_LESS "9.9.9")
set(PACKAGE_VERSION_COMPATIBLE True)
endif()
where 9.9.9 is replaced by the numeric version of the package. The
second file, t-config.cmake
, tells the client what the assorted
includes/libs are for the package by setting variables
t_INCLUDE_DIRS
, t_LIBRARIES
and so forth. The user passes
these values to cmake’s include_directories()
and
target_link_libraries()
.
Finding ROS by component (recommended method)¶
If you want to specify a dependency on several ROS components
simultaneously, use
find_package(ROS [XX.YY] REQUIRED COMPONENTS comp1 comp2)
, e.g.:
find_package(ROS REQUIRED COMPONENTS
cpp_common rostime roscpp_traits
roscpp_serialization sensor_msgs)
include_directories(${ROS_INCLUDE_DIRS})
add_executable(myexec ...)
target_link_libraries(${ROS_LIBRARIES})
See the cmake documentation for find_package()
for more details.
Your CMAKE_PREFIX_PATH
will need to point to a ROS installation.
The version string is as yet to be determined; “electric”, for
instance, is not a valid version. We will have to establish some
mapping between ROS versions and a numeric version of only numbers and
dots.