including external libraries in cmakelists.txt file - c++

Question

I'm using cmake to build an executable to run on an Intel Galileo board.
My question is how do I include the external mraa library in the build process.
Mraa library
When I download the library from git (1) do I need to build it as described here
Mraa compiling instructions
What do I need to put in my CMakeLists.txt file to pick up the library?
This is what I have thus far in my CMakeLists.txt file but I believe it is incorrect.
### MRAA ###
add_subdirectory(mraa-master/src)
file(GLOB mraa_SRC
"mraa-master/src/*.c"
)
include_directories( "${PROJECT_SOURCE_DIR}/mraa-master/include" )
add_library( ${MRAA_LIBRARY_NAME} SHARED ${mraa_SRC} )
Thank you
cmake_minimum_required(VERSION 2.8)
MESSAGE( STATUS "Starting build process")
SET( CMAKE_VERBOSE_MAKEFILE on )
if (CMAKE_BUILD_TYPE EQUAL "Debug")
MESSAGE(STATUS "Building in debug mode")
elseif (CMAKE_BUILD_TYPE EQUAL "Release")
MESSAGE(STATUS "Building in release mode")
endif()
SET(PROJECT_NAME "TestProject")
SET(APPLICATION_NAME "TestApplication")
SET(SAFE_STRING_LIBRARY "SafeString")
SET(APPLICATION_LIBRARY "Applibrary")
PROJECT( ${PROJECT_NAME} )
MESSAGE( STATUS "PROJECT: " ${PROJECT_NAME} )
SET(WRSDK_PATH "$ENV{WINDRIVER_SDK_DIR}")
IF (WRSDK_PATH)
else()
SET(WRSDK_PATH /opt/windriver/wrlinux/5.0-intel-quark/)
endif()
SET(APPLIBRARY_NAME ${APPLICATION_LIBRARY} )
SET(SAFE_STRING_LIBRARY_NAME ${SAFE_STRING_LIBRARY} )
### SAFE STRING ###
add_subdirectory(SafeStringStaticLibrary/safeclib)
file(GLOB safestring_SRC
"SafeStringStaticLibrary/safeclib/*.c"
)
include_directories( "${PROJECT_SOURCE_DIR}/SafeStringStaticLibrary /safeclib" )
add_library( ${SAFE_STRING_LIBRARY_NAME} SHARED ${safestring_SRC} )
include(ExternalProject)
ExternalProject_Add(mraa
GIT_REPOSITORY https://github.com/intel-iot-devkit/mraa.git
GIT_TAG v0.8.0
UPDATE_COMMAND ""
INSTALL_COMMAND "" )
file(GLOB app_SRC
"classes/*.cpp"
"Logger.cpp"
"sqlite3.c"
"shell.c"
)
add_library( ${APPLIBRARY_NAME} SHARED ${app_SRC})
include_directories( "${CMAKE_SOURCE_DIR}" "${CMAKE_SOURCE_DIR}/SafeStringStaticLibrary/include" )
add_executable( ${APPLICATION_NAME} ${APPLICATION_NAME}.cpp
include_directories( "${CMAKE_SOURCE_DIR}" "${CMAKE_SOURCE_DIR}/SafeStringStaticLibrary/include" "${CMAKE_SOURCE_DIR}/classes")
TARGET_LINK_LIBRARIES( ${APPLICATION_NAME} ${APPLIBRARY_NAME} ${SAFE_STRING_LIBRARY_NAME} -lrt -lpthread -lgcov -ldl)

Answer 1

The simplest way for build your project alongside with 3d party project is add_subdirectory() that subproject. Approach below implies that you (manually) download(git clone) sources of mraa project into mraa-lib subdirectory of your project's sources.
CMakeLists.txt:
cmake_minimum_required(VERSION 2.8)
MESSAGE( STATUS "Starting build process")
# Configure subproject before definition of variables for main project.
#
# Subproject defines *mraa* library target.
add_subdirectory(mraa-lib)
# Before installation, public mraa headers are contained under *api* subdirectory.
include_directories(mraa-lib/api)
... # create executable ${APPLICATION_NAME}
# Linking with mraa library is straightforward.
target_link_libraries(${APPLICATION_NAME} mraa)
That way mraa subproject will be configured, built and installed alongside with your project. So, if you cross-compile your project(using toolchain file, or inside IDE), the subproject will also be cross-compiled.