CMake/Examples

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

SET(VARIABLE VALUE)

View a CMake variable

MESSAGE("CMAKE_BINARY_DIR: ${CMAKE_BINARY_DIR}")

View a system variable

MESSAGE("$ENV{PATH}")

Check operating system

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

Check operating system

IF(CMAKE_SYSTEM_NAME STREQUAL Linux)

Outputs

Message

MESSAGE("Hello world")

Error

MESSAGE(FATAL_ERROR "An error occured.")

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:

FIND_PACKAGE(Eigen3)

Checking if a package was found

Most of the time the [PackageName]_FOUND variable is defined. You can use it like this: FIND_PACKAGE(Eigen3) if(EIGEN3_FOUND)

... do something ...

endif(EIGEN3_FOUND)

Suppress warnings

Sometimes you may want to optionally include a package. You can suppress the warning about the package not being found with: FIND_PACKAGE(Eigen3 QUIET)

Fix Mininum Version Error/Warning

cmake_minimum_required(VERSION 2.6.0 FATAL_ERROR)

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

INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR})

or

INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})

Set Link Directories

If a library you are using does not have a [LibraryName].cmake, you can do

find_library(OPENSSL_LIB ssl $ENV{OPENSSL_LIB_PATH})

This will check the environment for a variable named OPENSSL_LIB_PATH. If it exists, you can then use

target_link_libraries(mytarget ${OPENSSL_LIB})

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.

INCLUDE_DIRECTORIES(/some/directory)

View the directories that are set

get_property(inc_dirs DIRECTORY PROPERTY INCLUDE_DIRECTORIES)
message("inc_dirs = ${inc_dirs}")

Automate configure and generate

Note 'cmake' instead of 'ccmake' (ccmake is curses cmake (curses is the terminal gui))

cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/usr/mylocation ../

Compiler options

Set a cmake flag

ccmake ../../src/boost -DCMAKE_IS_EXPERIMENTAL=YES_I_KNOW

Set a cpp flag

SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D__WXGTK__")

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:

set(MySources main.c anotherFile.c)
add_executable(SpinRecognize ${MySource})
set_source_files_properties(${MySources} PROPERTIES LANGUAGE CXX)

Per-target

set_target_properties(myexe_target
                                PROPERTIES COMPILE_FLAGS "-Wall")

Set the default build type

SET(CMAKE_BUILD_TYPE Debug CACHE STRING "default to debug" FORCE)

Custom variable

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

String

SET(BUILD_PARAVIEW_PLUGIN ON CACHE STRING "Build Paraview plugin?" FORCE)

Bool

SET(DAI_WITH_BP ON CACHE BOOL "Belief Propagation" FORCE)

Comparison

if(DAI_WITH_BP EQUALS ON)
 #do something
endif(DAI_WITH_BP EQUALS ON)

This is equivalent to

if(DAI_WITH_BP)
 #do something
endif(DAI_WITH_BP)