Compiling 32-bit vs 64-bit project using CMake

Question

How do I specify that CMake should use a different link_directories value depending on whether the target is 32-bit or 64-bit? For example, 32-bit binaries need

Answer 1

Based on rominf I turned up following solution (for Windows). I install boost libraries into: C:\Boost_32 and C:\Boost_64

In CMakeLists.txt

math(EXPR BITS "8*${CMAKE_SIZEOF_VOID_P}")
set(BOOST_ROOT C:/Boost_${BITS})  

find_package(Boost 1.64.0 COMPONENTS ... )

INCLUDE_DIRECTORIES( ${Boost_INCLUDE_DIR}  )
LINK_DIRECTORIES(${Boost_LIBRARY_DIR})

Explanation:

• CMAKE_SIZEOF_VOID_P is equal to 4 on 32bit platform, and 8 on 64bit platform.
• Expression 8*${CMAKE_SIZEOF_VOID_P} will evaluate to 32 or 64, respectively.
• C:/Boost_${BITS} turns into C:/Boost_32 or C:/Boost_64 automagically

Advantages:

• You don't need conditionals (and in my CMakeLists there are too many already),
• It is 90% how you 'should' include Boost with CMake.