CMake link to external library

Question

How to get CMake to link an executable to an external shared library that is not build within the same CMake project?

Just doing target_link_libraries(GLBall ${CMAKE_BINARY_DIR}/res/mylib.so) gives the error

make[2]: *** No rule to make target `res/mylib.so', needed by `GLBall'.  Stop.
make[1]: *** [CMakeFiles/GLBall.dir/all] Error 2
make: *** [all] Error 2
(GLBall is the executable)

after I copied the library into the binary dir bin/res.

I tried using find_library(RESULT mylib.so PATHS ${CMAKE_BINARY_DIR}/res)

Which fails with RESULT-NOTFOUND.

Answer 1

arrowdodger's answer is correct and preferred on many occasions. I would simply like to add an alternative to his answer:

You could add an "imported" library target, instead of a link-directory. Something like:

# Your-external "mylib", add GLOBAL if the imported library is located in directories above the current.
add_library( mylib SHARED IMPORTED )
# You can define two import-locations: one for debug and one for release.
set_target_properties( mylib PROPERTIES IMPORTED_LOCATION ${CMAKE_BINARY_DIR}/res/mylib.so )

And then link as if this library was built by your project:

TARGET_LINK_LIBRARIES(GLBall mylib)

Such an approach would give you a little more flexibility: Take a look at the add_library( ) command and the many target-properties related to imported libraries.

I do not know if this will solve your problem with "updated versions of libs".