How to check if find_package found the package (boost)

Question

I want to not add boost.cxx if cmake find_package found no boost installed. Does find_package return something that I can wrap in condition to compile boost.cxx or not. Here is my current cmake file:

add_executable (complex complex.cxx lexer.cxx boost.cxx ../../src/lili.cxx ../../src/lilu.cxx)  # Make sure the compiler can find all include files include_directories (../../src)  include_directories (.)  # Make sure the linker can find all needed libraries # rt: clock_gettime() target_link_libraries(complex rt)  # Install example application install (TARGETS complex          RUNTIME DESTINATION bin)  IF(UNIX)     find_package(Boost COMPONENTS system filesystem REQUIRED)      ## Compiler flags     if(CMAKE_COMPILER_IS_GNUCXX)         set(CMAKE_CXX_FLAGS "-O2")         set(CMAKE_EXE_LINKER_FLAGS "-lsqlite3 -lrt -lpthread")     endif()      target_link_libraries(complex        ${Boost_FILESYSTEM_LIBRARY}       ${Boost_SYSTEM_LIBRARY}       #${PROTOBUF_LIBRARY}     ) ENDIF(UNIX) 

Answer 1

The FindXXX scripts are supposed to set a variable <Packagename>_FOUND to TRUEif the package was found. So in your case, it will set Boost_FOUND if boost was found.

When compiling your Boost.cxx, I assume that you will need Boost headers as well, so you should adjust your include directories as well.*

look for Boost before creating your executable. Furhtermore, you need to set your include directories before adding the executable.

IF(UNIX)     find_package(Boost COMPONENTS system filesystem REQUIRED)     # IF( Boost_FOUND ) # checking this variable isnt even necessary, since you added                         # REQUIRED to your call to FIND_PACKAGE         SET( BOOST_SRC_FILES boost.cxx )         INCLUDE_DIRECTORIES( ${Boost_INCLUDE_DIRS} ) # you could move this down as well                                                      # as ${Boost_INCLUDE_DIRS} will be                                                      # empty if Boost was not found     # ENDIF() ENDIF()  add_executable (complex complex.cxx lexer.cxx ${BOOST_SRC_FILES} ../../src/lili.cxx ../../src/lilu.cxx)  # Make sure the compiler can find all include files include_directories (../../src)  include_directories (.) # INCLUDE_DIRECTORIES( ${Boost_INCLUDE_DIRS} ) # alternative location to                                                 # add include dirs, see above  # Make sure the linker can find all needed libraries # rt: clock_gettime() target_link_libraries(complex rt)  # Install example application install (TARGETS complex          RUNTIME DESTINATION bin)  IF(UNIX)      ## Compiler flags     if(CMAKE_COMPILER_IS_GNUCXX)         set(CMAKE_CXX_FLAGS "-O2")         set(CMAKE_EXE_LINKER_FLAGS "-lsqlite3 -lrt -lpthread")     endif()      target_link_libraries(complex        ${Boost_FILESYSTEM_LIBRARY}       ${Boost_SYSTEM_LIBRARY}       #${PROTOBUF_LIBRARY}     ) ENDIF(UNIX) 

Afternote: Since you use the REQUIRED flag when looking for Boost (since you only need it on Unix platform) it is even sufficient to use the optional-source-files-in-a-variable trick.

(*) Thanks to your question, I just found out that it doesn't matter whether include_directories(...) is called before or after creating the target with ADD_EXECUTABLE or ADD_LIBRARY since the directories are added to all targets in the same project.