CMake and FIND PACKAGE

From Wiki for iCub and Friends
Jump to: navigation, search

CMake allows you to configure your project to use additional packages by calling the FIND_PACKAGE macro. Since this macro can be confusing I try to explain here how it works and how we have been using it on YARP.

Note: I here explain the functionalities of FIND_PACKAGE that are used in YARP, go to http://www.cmake.org for a more complete explanation.


FIND_PACKAGE(<name>) asks CMake to find and load settings from the external package <name>. This works as follows:

  • CMake searches the directories listed in CMAKE_MODULE_PATH for a file called Find<name>.cmake. If found, this macro is executed and it is responsible for finding the package (examples of similar macro are: FindACE.cmake, FindBoost.cmake, FindOpenCV.cmake that are located in your $YARP_ROOT/conf directory). "Find" macros define variables which allow you to check if the package has been found and use it in your project. Unfortunately different macros behave differently so you have to check the code to find out the exact names of those variables (usually this is explained in the comments at the beginning of the file). For example, a Find macro might define:
  <name>_FOUND  // true iff the package was found
  <name>_INCLUDE_DIR   // a list of directories containing the package's include files
  <name>_LIBRARIES     // a list of directories containing the package's libraries
  <name>_LINK_DIRECTORIES  // the list of the package's libraries

Now suppose you want to create a new project which uses OpenCV. A possible CMakeLists.txt is:

  #### assume FindOpenCV.cmake is in one of the CMAKE_MODULE_PATH folders.
  FIND_PACKAGE(OpenCV)
  
  # searches for all .cpp and .h files in the current directory and add them 
  # to the current project
  FILE(GLOB folder_source *.cpp)
  FILE(GLOB folder_header *.h)
  SOURCE_GROUP("Source Files" FILES ${folder_source})
  SOURCE_GROUP("Header Files" FILES ${folder_header})
  
  # create the project
  ADD_EXECUTABLE(your_project ${folder_source} ${folder_header})
   
  # add include directories
  INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR})
  INCLUDE_DIRECTORIES(${OPENCV_INCLUDE_DIR})
   
  # link opencv libraries 
  TARGET_LINK_LIBRARIES(your_project ${OPENCV_LIBRARIES})
  • If CMake does not find any Find<name>.cmake file in the directories listed in MAKE_MODULE_PATH, it assumes the package was built with CMake and has a "<name>Config.cmake" file associated. CMake expects the user to specify the location of this file by filling a cache entry called <name>_DIR (this entry is created by CMake automatically). If the file is found, it is processed to load the settings of the package (an error or a warning is displayed otherwise).

For example, when YARP is built CMake creates a file called YARPConfig.cmake in the "build" directory that is selected by the user. When users want to create a project which uses YARP they just have to call FIND_PACKAGE(YARP) and select the approprite YARP_DIR. For example:

  SET(YARP_DIR "c:/yarp/build" CACHE LOCATION "where was yarp built?")
  
  or, if they YARP_ROOT is an environment variable pointing to your YARP build:
  
  SET(YARP_DIR "$ENV{YARP_ROOT}" CACHE LOCATION "where was yarp built?")
  
  FIND_PACKAGE(YARP)

The macro FIND_PACKAGE automatically searches YARP_DIR for the file YARPConfig.CMake and executes it. YARPConfig.cmake creates the entries YARP_LIBRARIES, YARP_INCLUDE_DIRS and YARP_DEFINES. To use these in a project, do:

  INCLUDE_DIRECTORIES(${YARP_INCLUDE_DIRS})
  ADD_DEFINITIONS(${YARP_DEFINES}) # optional
  ...
  TARGET_LINK_LIBRARIES(your_target_name ${YARP_LIBRARIES})




To recap, as a final example here is a CMakeLists.txt which creates a new project "foo" which uses YARP and OpenCV. You'll need to have the environment variable YARP_DIR set to where YARP was built:

  CMAKE_MINIMUM_REQUIRED(VERSION 2.6)
  
  # execute YarpConfig.cmake
  FIND_PACKAGE(YARP)
  
  # pick up YARP find scripts
  SET(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${YARP_MODULE_PATH})
  
  # now FindOpenCV.cmake is in CMAKE_MODULE_PATH
  FIND_PACKAGE(OpenCV)
  
  # searches for all .cpp and .h files in the current directory and add them 
  # to the current project
  FILE(GLOB folder_source *.cpp)
  FILE(GLOB folder_header *.h)
  SOURCE_GROUP("Source Files" FILES ${folder_source})
  SOURCE_GROUP("Header Files" FILES ${folder_header})
  
  # add the current directory in the include path
  INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR})
  # add YARP include directories
  INCLUDE_DIRECTORIES(${YARP_INCLUDE_DIRS})
  # add OpenCV include directories
  INCLUDE_DIRECTORIES(${OPENCV_INCLUDE_DIR})
   
  # create the program "foo"
  ADD_EXECUTABLE(foo ${folder_source} ${folder_header})
   
  # link opencv and YARP libraries
  TARGET_LINK_LIBRARIES(foo ${OPENCV_LIBRARIES} ${YARP_LIBRARIES})
Personal tools
Namespaces

Variants
Actions
Navigation
Print/export
Toolbox