CMake/Examples

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Welcome to the CMake Wiki Examples! These short snippets which show you how to perform many common CMake procedures. Please see [1] for the verbose documentation.

Please add examples as you find common procedures which are not explained here!

Basics

Set a CMake variable

<source lang="cmake"> SET(VARIABLE VALUE) </source>

View a CMake variable

<source lang="cmake"> MESSAGE("CMAKE_BINARY_DIR: ${CMAKE_BINARY_DIR}") </source>

View a system variable

<source lang="cmake"> MESSAGE("$ENV{PATH}") </source>

Check operating system

<source lang="cmake"> 

IF(WIN32)
  ...do something...
ELSE(WIN32)
  ...do something else...
ENDIF(WIN32)

</source>

Check operating system

<source lang="cmake"> IF(CMAKE_SYSTEM_NAME STREQUAL Linux) </source>

Lists

Check if a list contains a value

<source lang="cmake"> list(FIND VTK_MODULES_ENABLED "vtkFiltersParallel" HasMyModule)

IF(HasMyModule EQUAL -1) 

 message(FATAL_ERROR "You must build VTK with more modules.")

ENDIF() </source>

Outputs

Message

<source lang="cmake"> MESSAGE("Hello world") </source>

Output a Variable

<source lang="cmake"> message("VTK Using Boost? ${VTK_USE_BOOST}") </source>

Error

<source lang="cmake"> MESSAGE(FATAL_ERROR "An error occured.") </source>

Conditional Statement (if)

There are two allowable syntaxes:

<source lang="cmake"> if(something) 

do something

else(something) # the argument must match the if(...) 

do something else

endif(something) # the argument must match the if(...) </source>

The following is also allowed. It is easier to read (because "else(the same thing)" doesn't really make sense if you read it like c++, for example), but it is also easier to confuse yourself with nested ifs. <source lang="cmake"> if(something) 

do something

else() 

do something else

endif() </source>

Example: <source lang="cmake"> if (!VTK_USE_BOOST) 

 MESSAGE(SEND_ERROR "VTK must be built with VTK_USE_BOOST=ON.")

endif () </source>

Logical Operators

These operators work exactly as you would expect.

AND

if(A AND B)

OR

if(A OR B)

NOT

if(NOT A)

Compound

if(NOT(A AND B))

Finding Packages

Most of the time large packages will have their Find[PackageName].cmake file included in the cmake distribution. If that is the case, all you must do it: <source lang="cmake"> FIND_PACKAGE(Eigen3) </source>

Specifying where to look for .cmake files

If you place your FindXYZ.cmake and UseXYZ.cmake files in the same directory as your main CMakeLists.txt file, you can tell CMake to try to use them first before looking at system paths by doing: <source lang="cmake"> set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/" ${CMAKE_MODULE_PATH}) </source>

Checking if a package was found

Most of the time the [PackageName]_FOUND variable is defined. You can use it like this: <source lang="cmake"> FIND_PACKAGE(Eigen3) if(EIGEN3_FOUND) 

... do something ...

endif(EIGEN3_FOUND) </source>

Suppress warnings

Sometimes you may want to optionally include a package. You can suppress the warning about the package not being found with: <source lang="cmake"> FIND_PACKAGE(Eigen3 QUIET) </source>

Fix Mininum Version Error/Warning

<source lang="cmake"> cmake_minimum_required(VERSION 2.6.0 FATAL_ERROR) </source>


Look in the directory that the CMakeLists.txt file is for header and implementation files

<source lang="cmake"> INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}) </source>

or

<source lang="cmake"> INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR}) </source>

Set Link Directories

If a library you are using does not have a [LibraryName].cmake, you can do <source lang="cmake"> find_library(OPENSSL_LIB ssl $ENV{OPENSSL_LIB_PATH}) </source> This will check the environment for a variable named OPENSSL_LIB_PATH. If it exists, you can then use <source lang="cmake"> target_link_libraries(mytarget ${OPENSSL_LIB}) </source>

If it does not, it can be set through the CMake GUI.

Set Include Directories

This command adds a path to the include directories, you do NOT have to do the 'export' style ``keep everything that is here and add this one syntax. <source lang="cmake"> INCLUDE_DIRECTORIES(/some/directory) </source>

View the directories that are set

<source lang="cmake"> get_property(inc_dirs DIRECTORY PROPERTY INCLUDE_DIRECTORIES) message("inc_dirs = ${inc_dirs}") </source>

Automate configure and generate

Note 'cmake' instead of 'ccmake' (ccmake is curses cmake (curses is the terminal gui)) <source lang="cmake"> cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/usr/mylocation ../ </source>

Compiler options

Set a cmake flag

<source lang="cmake"> ccmake ../../src/boost -DCMAKE_IS_EXPERIMENTAL=YES_I_KNOW </source>

Set a cpp flag/preprocessor definition

<source lang="cmake"> SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D__WXGTK__") </source>

Force g++

Ocassionally you will come across files with the extension .c that actually contain c++ code. CMake treats the file based on its extension. If you want to override this behavior (in this case, compile .c files with your c++ compiler), do the following:

<source lang="cmake"> set(MySources main.c anotherFile.c) add_executable(SpinRecognize ${MySource}) set_source_files_properties(${MySources} PROPERTIES LANGUAGE CXX) </source>

Per-target

<source lang="cmake"> set_target_properties(myexe_target 

                               PROPERTIES COMPILE_FLAGS "-Wall")

</source>

Set the default build type

<source lang="cmake"> SET(CMAKE_BUILD_TYPE Debug CACHE STRING "default to debug" FORCE) </source>

Custom variable

Here is a list of supported variable types: http://www.cmake.org/cmake/help/cmake2.6docs.html#command:set

String

<source lang="cmake"> SET(BUILD_PARAVIEW_PLUGIN ON CACHE STRING "Build Paraview plugin?" FORCE) </source>

Bool

<source lang="cmake"> SET(DAI_WITH_BP ON CACHE BOOL "Belief Propagation" FORCE) </source>

Comparison

<source lang="cmake"> if(DAI_WITH_BP EQUALS ON) 

#do something

endif(DAI_WITH_BP EQUALS ON) </source>

This is equivalent to

<source lang="cmake"> if(DAI_WITH_BP) 

#do something

endif(DAI_WITH_BP) </source>

Linking to specific libraries

ITK

Add the path to your environment: <source lang="text"> export ITK_DIR=/home/doriad/bin/ITK </source>

Then in the CMakeLists.txt use: <source lang="cmake"> FIND_PACKAGE(ITK REQUIRED) INCLUDE(${ITK_USE_FILE})

ADD_EXECUTABLE(CastImageFilter CastImageFilter.cxx) TARGET_LINK_LIBRARIES(CastImageFilter vtkHybrid ITKIO ITKBasicFilters ITKCommon ) </source>

VXL

Add the path to your environment: <source lang="text"> export VXLBIN="/home/doriad/bin/vxl" </source>

Then in the CMakeLists.txt use: <source lang="cmake"> FIND_PACKAGE(VXL REQUIRED) INCLUDE(${VXL_CMAKE_DIR}/UseVXL.cmake) </source>

VTK

Add the path to your environment: <source lang="text"> export VTK_DIR="/home/doriad/bin/VTK" </source>

Then in the CMakeLists.txt use: <source lang="cmake"> FIND_PACKAGE(VTK REQUIRED) INCLUDE(${VTK_USE_FILE}) </source>

Boost

Lets assume we built boost with ./bjam --prefix=/home/doriad/bin install

Then for CMake to find Boost, all you need is to add to your .bashrc: <source lang="text"> export BOOST_ROOT="/home/doriad/bin" </source>

Then in the CMakeLists.txt use: <source lang="cmake"> SET(Boost_USE_MULTITHREAD ON) #set a flag FIND_PACKAGE(Boost) INCLUDE_DIRECTORIES(${INCLUDE_DIRECTORIES} ${Boost_INCLUDE_DIRS}) LINK_DIRECTORIES(${LINK_DIRECTORIES} ${Boost_LIBRARY_DIRS}) </source>

OpenCV

Add to the environment: <source lang="text"> export OpenCV_DIR=/home/doriad/bin/OpenCV </source>

Then in the CMakeLists.txt use: <source lang="cmake"> FIND_PACKAGE(OpenCV REQUIRED ) INCLUDE_DIRECTORIES( ${OPENCV_INCLUDE_DIR} )

ADD_EXECUTABLE(Scalar Scalar.cxx) TARGET_LINK_LIBRARIES(Scalar ${OpenCV_LIBS}) </source>

Get Help Using a Library

<source lang="cmake"> cmake --help-module FindBoost </source>

Add new libraries to CMake

<source lang="cmake"> /usr/share/cmake/Modules/FindOpenGL.cmake| </source>

Dependency Graph

<source lang="cmake"> ccmake ../src/Program/ --graphviz=test.graph dotty test.graph </source>

CTest

Run a specific test by number

e.g. Test 622 <source lang="cmake"> ctest -I 622,622 </source>

Run a range of tests

e.g. Test 622 to 625 <source lang="cmake"> ctest -I 622,625 </source>

Run a test by name

<source lang="cmake"> ctest -R "itkTransformPoint*"| </source>

Show verbose output of a test

<source lang="cmake"> ctest -V -R "itkTransformPoint*"| </source>

Create a Test

<source lang="cmake"> cmake_minimum_required(VERSION 2.6)

project(simple) ENABLE_TESTING()

add_executable(simple simple.cpp) add_test(SimpleTest simple) </source>

Link to a library

<source lang="cmake"> ADD_EXECUTABLE(ColoredLines ColoredLines.cpp) TARGET_LINK_LIBRARIES(ColoredLines vtkHybrid) </source>


Create a library

<source lang="cmake"> add_library(MatlabLibrary ./MatlabDll/LidarK.cpp) </source>

Installing executables

Once your project is built, you can use the 'install' make target to copy the executables to the directory specified by CMAKE_INSTALL_PREFIX.

<source lang="cmake"> add_executable(test test.cxx) install(TARGETS test RUNTIME DESTINATION ${CMAKE_INSTALL_PREFIX}) </source>

If you get an error like: 

error while loading shared libraries: I get
libwx_gtk2u_core-2.9.so.1: cannot open shared object file: No such file or directory

you should add: 

SET(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)

to your CMakeLists.txt file.

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