Sometimes you need to link one library on Windows and another on Linux (or vice versa). CMake has a number of variables that allow you to do this easily:
| UNIX | TRUE on all UNIX-like OS’s including Apple OS X and CygWin |
| WIN32 | TRUE on Windows including CygWin |
| APPLE | TRUE on Apple systems. ** |
| MINGW | TRUE when using the MinGW compiler in Windows |
| MSYS | TRUE when using the MSYS developer environment in Windows |
| CYGWIN | TRUE on Windows when using the CygWin version of cmake |
** Note this does not imply the system is Mac OS X only that APPLE is #defined in C/C++ header files. Obtain more specific system information via CMAKE_SYSTEM_VERSION. I.e. IF(${CMAKE_SYSTEM_NAME} MATCHES “Darwin”) then it’s Mac OS X
CMake sets these variables for you. You can use them in your CMake scripts to do specific functions only under a specific Operating System.
IF (WIN32)
message(STATUS "Microsoft Windows. Building Win32SupportLibrary.")
add_subdirectory(Win32SupportLibrary)
ELSEIF (UNIX AND NOT MINGW)
message(STATUS "Building on Linux. Expecting support to be installed.")
ENDIF()That’s it! Now you have platform specific build functions.