[CMake] Include_directories looks for Boost twice / Problem with if statement

[Raymond Wan]

Hi all,

I have two CMakeFile.txt's for a C++ project where one includes the
other.  In both cases, I'm searching for Boost.

So, to make this easier, suppose I call one project "parent" and the
other "child" such that "parent"'s CMakefile.txt has:

INCLUDE_DIRECTORIES (child)

where child is a subdirectory.  Both have:

ADD_DEFINITIONS (-DBOOST_ALL_NO_LIB)
SET (BOOST_ROOT $ENV{BOOST_ROOT})
SET (Boost_NO_SYSTEM_PATHS ON)
SET (Boost_USE_MULTITHREADED ON)
SET (Boost_USE_STATIC_RUNTIME OFF)
FIND_PACKAGE (Boost 1.42.0 REQUIRED COMPONENTS system)
IF (Boost_FOUND)
  IF (TARGET parent)
    LINK_DIRECTORIES (${Boost_LIBRARY_DIRS})
    INCLUDE_DIRECTORIES (${Boost_INCLUDE_DIRS})
    TARGET_LINK_LIBRARIES (parent ${Boost_LIBRARIES})
  ENDIF (TARGET parent)
ENDIF ()

(In the subdirectory "child", I check for the target "child" instead.)

The reason I have to repeat it twice is because both parent and child
has a main ().  parent has the one for the entire project; if I want
to do unit testing on child, then I compile in child's build directory
using its main.

I hope everything so far is ok.  The problem is that when I run the
CMakeFile.txt of parent, it ends up checking for Boost twice.

There's no harm to it and I had left it alone for a while.  Then, I
thought I could use an if statement inside child to prevent it from
checking again.  Inside, child, none of these seem to work:

IF (NOT DEFINED Boost_FOUND)
IF (NOT Boost_FOUND)

So, while my question is about Boost, I guess it is irrelevant to
boost...seems to be a problem with my understanding of variables and
if statements.

Any suggestion on what I'm doing wrong?  Or am I going at it wrong and
I need to rethink what I'm doing?

Thank you!

Ray