Set output directory for CMake OBJECT libraries - cmake

Question

In my CMake file I've specified an object library:
add_library(core OBJECT ${sourcefiles})
I refer to this set of object file in a shared library further on:
add_library(sharedlib SHARED $<TARGET_OBJECTS:core>)
This works fine, however I would like to reuse the build artefacts between different project.
By setting the LIBRARY_OUTPUT_PROPERTY on the sharedlib I can direct the generated .so file to a common directory:
set_target_properties(sharedlib PROPERTIES LIBRARY_OUTPUT_NAME /commondir)
However, I cannot seem to do the same thing for the core (OBJECT) library - the .o files always end up in the (project-specific) generated cmake-build directories.
This means every project will have to rebuild the (large) shared library anyway...
Am I doing something wrong, or is this not (yet?) possible with CMake?

Answer 1

You can't change the output directory of object/intermediate files in CMake. That's by design (to allow several identical output names in one project):
"There is no way to change that name.
CMake creates an exact copy of the source tree in
the binary tree."
But with version 3.9 CMake learned to export object libraries:
cmake_minimum_required(VERSION 3.9)
project(CorePorject)
file(WRITE "core.cpp" "")
file(WRITE "helper.cpp" "")
set(sourcefiles "core.cpp" "helper.cpp")
add_library(core OBJECT ${sourcefiles})
export(
TARGETS core
FILE core.cmake
NAMESPACE Core_
)
References
Set C++ object file output location with CMake
Set the directory for Intermediate files (like .obj) in CMake
Making cmake library accessible by other cmake packages automatically