[Cmake] Setting Variables in CMAKE

[Linton, Tom]

I have a source tree with a top level CMakeLists.txt file that contains
something like:

    INCLUDE(${CMAKE_ROOT}/Modules/CMakeDetermineSystem.cmake)
    SET(MYFLAG "defaultValue")
    IF(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
       SET(MYFLAG "linuxValue")
    ENDIF(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
    PROJECT(TRY)
    SUBDIRS(a b)

The behavior of CMAKE is that (1) in the top-level CMakeLists.txt the =
variable
"MYFLAG" gets set to "linuxValue" wherease (2) in the subdirectories
"MYFLAG" is left at "defaultValue".=20

I tried changing the SET command like:=20
    SET(MYFLAG "defaultValue" CACHE INTERNAL "myflag")
but this had no effect.

I want to set variables at top-level based on the system name and have =
these
variables propagate to the subdirectories and it seems like what I'm =
doing is
correct, according to section 3.4 in the CMake book, which say that =
variable
scope is limited to a CMakeList file and any subdirectory CMakeList =
files.

This seems like a really basic thing to want to do. Any suggestions on
what's going wrong?

Thanks

Tom