How to add include directories from ExternalProject_Add into project? - cmake

Question

I have tried following this solution this individual has from this question. I am trying to do this with boost with the following cmake file in a separate directory from my Source:
#---------------------------------------------------------------------------
# Get and build boost
SET_PROPERTY(DIRECTORY PROPERTY "EP_BASE" ${ep_base})
SET(boost_GIT_TAG "origin/master")
set( Boost_Bootstrap_Command )
if( UNIX )
set( Boost_Bootstrap_Command ./bootstrap.sh )
set( Boost_b2_Command ./b2 )
else()
if( WIN32 )
set( Boost_Bootstrap_Command bootstrap.bat )
set( Boost_b2_Command b2.exe )
endif()
endif()
ExternalProject_Add(Boost_external_Download
GIT_REPOSITORY "https://github.com/boostorg/boost.git"
GIT_TAG ${boost_GIT_TAG}
BUILD_IN_SOURCE 1
UPDATE_COMMAND ""
PATCH_COMMAND ""
CONFIGURE_COMMAND ${Boost_Bootstrap_Command}
BUILD_COMMAND ${Boost_b2_Command} install
--without-python
--without-mpi
--disable-icu
--prefix=${CMAKE_BINARY_DIR}/Boost
--threading=single,multi
--link=shared
--variant=release
-j8
INSTALL_COMMAND ""
INSTALL_DIR ""
)
if( NOT WIN32 )
set(Boost_LIBRARY_DIR ${CMAKE_BINARY_DIR}/Boost/lib/ )
set(Boost_INCLUDE_DIR ${CMAKE_BINARY_DIR}/Boost/include/boost/ )
else()
set(Boost_LIBRARY_DIR ${CMAKE_BINARY_DIR}/Boost/lib/ )
set(Boost_INCLUDE_DIR ${CMAKE_BINARY_DIR}/Boost/include/boost/ )
endif()
ExternalProject_Get_Property(Boost_external_Download BINARY_DIR)
SET(Boost_DIR ${BINARY_DIR} CACHE PATH "")
add_library(Boost_external SHARED IMPORTED)
The only thing that is different between one of the solutions and mine is that I don't have the set_target_properties right after I add the library. Since boost has a lot of libraries in there and I am not exactly sure what needs to be added.
In my Source Folder, my CMakeLists.txt does the following:
include_directories(${Boost_INCLUDE_DIR})
add_executable(Main main.cpp)
target_link_libraries(Main Boost_external)
add_dependencies(Main Boost_external_Download)
However, in main.cpp when I use #include <boost/process.hpp> just to see if it links, I get the error that #include <boost/process.hpp> no such file or directory. When I try to make the project. I am not really sure where I am going wrong with this so any helpful advice would be appreciated.
Edit: structure
Root Folder
|
- CmakeLists.txt
- Externals Directory
|
| - Externals.cmake
| - boostExternal.cmake
| - other external cmake files
- Source Directory
|
| - CmakeLists.txt
| - main.cpp
The Root Cmake calls the Externals.cmake file. Which then includes all the other Cmake files within that directory. Once those are finished, the root Cmake file add the directory Source, and that Cmake file has the call to include_directories(${Boost_INCLUDE_DIR}).