how to add prebuilt object files to executable in cmake

Question

I have an add_custom_target that triggers a make for a project (that project does not use cmake!) and generates an object file. I would like to add this object file to an executable target in my project's cmake. Is there a way to do this?

Answer 1

I've done this in my projects with target_link_libraries():

target_link_libraries(     myProgram      ${CMAKE_CURRENT_SOURCE_DIR}/libs/obj.o ) 

Any full path given to target_link_libraries() is assumed a file to be forwarded to the linker.

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For CMake version >= 3.9 there are the add_library(... OBJECT IMPORTED ..) targets you can use.

See Cmake: Use imported object

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And - see also the answer from @arrowd - there is the undocumented way of adding them directly to your target's source file list (actually meant to support object file outputs for add_custom_command() build steps like in your case).

Answer 2

SET(OBJS   ${CMAKE_CURRENT_SOURCE_DIR}/libs/obj.o )  ADD_EXECUTABLE(myProgram ${OBJS} <other-sources>)  SET_SOURCE_FILES_PROPERTIES(   ${OBJS}   PROPERTIES   EXTERNAL_OBJECT true   GENERATED true ) 

That worked for me. Apparently one must set these two properties, EXTERNAL_OBJECT and GENERATED.