Difference between revisions of "CMake and FIND PACKAGE"

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One of the most important features of CMake is that it allows to configure your project to include/link additional packages (libraries). To do this you have to tell CMake you want to use an additional package, you do this with the FIND_PACKAGE macro. I found FIND_PACKAGE a bit confusing so I try to explain here how it works and how we have been using it on YARP.
+
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.
 
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 projects/packages called <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). A Find macro might define for example:
+
FIND_PACKAGE(<name>) asks CMake to find and load settings from the external package <name>. This works as follows:
  
  <name>_FOUND  --> true of the package was found
+
* 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>_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
 
  
Suppose you want to include the ACE package in a new project:
+
  <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.
 
   #### assume FindOpenCV.cmake is in one of the CMAKE_MODULE_PATH folders.
Line 27: Line 28:
 
   ADD_EXECUTABLE(your_project ${folder_source} ${folder_header})
 
   ADD_EXECUTABLE(your_project ${folder_source} ${folder_header})
 
      
 
      
    add include directories
+
  # add include directories
 
   INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR})
 
   INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR})
 
   INCLUDE_DIRECTORIES(${OPENCV_INCLUDE_DIR})
 
   INCLUDE_DIRECTORIES(${OPENCV_INCLUDE_DIR})
Line 36: Line 37:
 
* 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).
 
* 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 selected by the user. When users want to create a project which uses YARP they do something like:
+
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?")
 
   SET(YARP_DIR "c:/yarp/build" CACHE LOCATION "where was yarp built?")
 
    
 
    
   or, if they defined YARP_ROOT:
+
   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?")
 
   SET(YARP_DIR "$ENV{YARP_ROOT}" CACHE LOCATION "where was yarp built?")
Line 46: Line 47:
 
   FIND_PACKAGE(YARP)
 
   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_INCLUDES and YARP_DEFINES which are already processed so that projects added later will use them:
+
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})
 +
 
 +
 
 +
----
  
  LINK_LIBRARIES(${YARP_LIBRARIES})
 
  INCLUDE_DIRECTORIES(${YARP_INCLUDES})
 
  ADD_DEFINITIONS(${YARP_DEFINES})
 
  
Note: LINK_LIBRARIES is an obsolete CMake command, in the future should be replaced with TARGET_LINK_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:
  
YARPConfig.cmake also append ${YARP_DIR}/conf to CMAKE_MODULE_PATH so that later all Find*.cmake provided with YARP can be accessed by CMake by calling FIND_PACKAGE command.
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  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})

Latest revision as of 20:25, 25 May 2010

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})