Cmake add external project? - cmake

Question

I'm not entirely sure if externalproject_Add as most of the examples I can find on it is about downloading git etc/but maybe thats it...
Esentially I have :
FolderA // inherited project
> main.cpp
> CMakeList.txt
> libFolder
>someStuff.h
>someStuff.cpp
FolderB // base project
> main.cpp
> CMakeList.txt
> libFolder_Core
>someStuff_Core.h
>someStuff_Core.cpp
I want to "not" have to build static/dynamic/etc lib every time I make a change to project in folderB, I just want to include the CMakeList.txt from that folder in my folderA, FolerB cmake only has something like
set(headers xx.h)
set(source xx.cpp)
set(all ${headers} ${source})
Just looking for a way to say in projectA, cmake,
get_filename_component(libs"${CMAKE_CURRENT_SOURCE_DIR}/.." ABSOLUTE)
SET(coreLib ${libs}/someCoreLib/)
add_executable(name, main.cpp ${coreLib})
Is something like that possible?

Answer 1

You can do that easily with mordern CMake using exported target.
In project A:
add_library(projecta a.cpp b.cpp c.cpp)
add_library(projecta::projecta ALIAS projecta)
target_include_directories(projecta PUBLIC ...)
install(TARGETS projecta EXPORT projectaTargets
LIBRARY DESTINATION lib
ARCHIVE DESTINATION lib
RUNTIME DESTINATION bin
INCLUDES DESTINATION include
)
install(
EXPORT projectaTargets
NAMESPACE projecta::
FILE projectaConfig.cmake
DESTINATION lib/cmake/projecta
)
export(
EXPORT projectaTargets
FILE "${CMAKE_CURRENT_BINARY_DIR}/projectaConfig.cmake"
)
This will make a target for projecta and export the targets for other project to use them.
If the project A itself has dependencies, consider exporting the targets to a target file, then generate a config file that also find the package of your dependencies. More on that on the It's Time To Do CMake Right blog post.
Simply add the path of your build directory in the CMake module path in the command line: -DCMAKE_PREFIX_PATH=/path/to/projecta/build
Then, in project B:
find_package(projecta REQUIRED)
add_executable(projectb x.cpp y.cpp z.cpp)
# link project b to project a,
# adding include directories and link dependencies
target_link_libraries(projectb PUBLIC projecta::projecta)