Link a shared library with CMake

Question

I'm trying to link in a pre-compiled shared library file called libtest-lib.so. This is what I have at the bottom of my CMakeLists.txt:

link_directories("/projectspath/LinkTest/TestLib/app/build/intermediates/cmake/debug/obj/armeabi-v7a")

add_library(testlib libtest-lib.so)

target_link_libraries(testlib libtest-lib.so)

As above, I get the following error:

CMake Error at CMakeLists.txt:49 (add_library):
  Cannot find source file:
    libtest-lib.so
  Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm     .hpp
  .hxx .in .txx
 CMake Error: CMake can not determine linker language for target:    testlib

If I comment out the add_library line, I get the following:

CMake Error at CMakeLists.txt:51 (target_link_libraries):
Cannot specify link libraries for target "testlib" which is not built by this project.

It seems that source files (.c, cpp, etc) are absolutely required when linking in a library. But how do I link in an .so file? The docs say the following about target_link_libraries():

The named must have been created in the current directory by a command such as add_executable() or add_library().

If I substitute add_library() with add_executable() I get the same error. What is the proper way to link an .so file in CMake?

Answer 1

I think that what you want is to import a library for CMake:

 add_library(testlib SHARED IMPORTED)
 set_property(TARGET testlib PROPERTY IMPORTED_LOCATION "/projectspath/LinkTest/TestLib/app/build/intermediates/cmake/debug/obj/armeabi-v7a/libtest-lib.so")

See https://gitlab.kitware.com/cmake/community/wikis/doc/tutorials/Exporting-and-Importing-Targets for more information

Answer 2

add_library creates a new library.

Instead you want to link your library to some other target.

Let's say

add_executable(main main.cpp)
target_link_libraries(main libtest-lib)

This should already work.