Platform detection in CMake

Here's an expanded version of KneLL's answer, also checking for Windows 10.

if(WIN32)
    macro(get_WIN32_WINNT version)
        if(CMAKE_SYSTEM_VERSION)
            set(ver ${CMAKE_SYSTEM_VERSION})
            string(REGEX MATCH "^([0-9]+).([0-9])" ver ${ver})
            string(REGEX MATCH "^([0-9]+)" verMajor ${ver})
            # Check for Windows 10, b/c we'll need to convert to hex 'A'.
            if("${verMajor}" MATCHES "10")
                set(verMajor "A")
                string(REGEX REPLACE "^([0-9]+)" ${verMajor} ver ${ver})
            endif()
            # Remove all remaining '.' characters.
            string(REPLACE "." "" ver ${ver})
            # Prepend each digit with a zero.
            string(REGEX REPLACE "([0-9A-Z])" "0\\1" ver ${ver})
            set(${version} "0x${ver}")
        endif()
    endmacro()

    get_WIN32_WINNT(ver)
    add_definitions(-D_WIN32_WINNT=${ver})
endif()

As karlphilip pointed out, you can use if(WIN32) for platform detection.

You'll have a number of possibilities for passing preprocessor defines to the application:

• Use a configure header that gets preprocessed by CMake's configure_file. This approach has the advantage that all #defines are actually part of the code and not of the build environment. The disadvantage is that it requires an (automatic) preprocessing step by CMake
• Use add_definitions. This will add the preprocessor flag for all source files in the project, so it's more of a quick and dirty approach.

• Use the COMPILE_DEFINITIONS property. This allows fine grained control over the defines on a per-file (and even per-config) basis: set_property(SOURCE ${YOUR_SOURCE_FILES} APPEND PROPERTY COMPILE_DEFINITIONS YOUR_FLAG1 YOUR_FLAG2)

  In modern CMake versions (2.8.12 and higher) you can also use the more convenient target_compile_definitions command for this.

I usually prefer the latter, but that's mostly a matter of personal taste.

Inside the CMakeLists.txt file you can do:

IF (WIN32)
  # set stuff for windows
ELSE()
  # set stuff for other systems
ENDIF()

Here is a simple solution.

macro(get_WIN32_WINNT version)
    if (WIN32 AND CMAKE_SYSTEM_VERSION)
        set(ver ${CMAKE_SYSTEM_VERSION})
        string(REPLACE "." "" ver ${ver})
        string(REGEX REPLACE "([0-9])" "0\\1" ver ${ver})

        set(${version} "0x${ver}")
    endif()
endmacro()

get_WIN32_WINNT(ver)
add_definitions(-D_WIN32_WINNT=${ver})