C++ – Link a shared library with CMake

ccmakeshared-libraries

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?

Best Answer

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

Related Solutions

C++ – CMake: Project structure with unit tests

For questions 1 & 2, I would recommend making a library from your non-test files excluding main.cpp (in this case just src/sqr.cpp and src/sqr.h), and then you can avoid listing (and more importantly re-compiling) all the sources twice.

For question 3, these commands add a test called "MyTest" which invokes your executable "test" without any arguments. However, since you've added these commands to test/CMakeLists.txt and not your top-level CMakeLists.txt, you can only invoke the test from within the "test" subdirectory of your build tree (try cd test && ctest -N). If you want the test to be runnable from your top-level build directory, you'd need to call add_test from the top-level CMakeLists.txt. This also means you have to use the more verbose form of add_test since your test exe isn't defined in the same CMakeLists.txt

In your case, since you're running cmake in the root folder, your build tree and your source tree are one and the same. This is known as an in-source build and isn't ideal, which leads to question 4.

The preferred method for generating the build tree is to do an out-of-source build, i.e. create a directory somewhere outside of your source tree and execute cmake from there. Even creating a "build" directory in the root of your project and executing cmake .. would provide a clean structure which won't interfere with your source tree.

One final point is to avoid calling executables "test" (case-sensitive). For reasons why, see this answer.

To achieve these changes, I'd do the following:

CMakeLists.txt:

cmake_minimum_required (VERSION 2.8)
project (TEST)
add_subdirectory (src) 
add_subdirectory (test)
enable_testing ()
add_test (NAME MyTest COMMAND Test)

src/CMakeLists.txt:

add_library (Sqr sqr.cpp sqr.h)
add_executable (demo main.cpp)
target_link_libraries (demo Sqr)

test/CMakeLists.txt:

find_package (Boost COMPONENTS system filesystem unit_test_framework REQUIRED)
include_directories (${TEST_SOURCE_DIR}/src
                     ${Boost_INCLUDE_DIRS}
                     )
add_definitions (-DBOOST_TEST_DYN_LINK)
add_executable (Test test.cpp)
target_link_libraries (Test
                       Sqr
                       ${Boost_FILESYSTEM_LIBRARY}
                       ${Boost_SYSTEM_LIBRARY}
                       ${Boost_UNIT_TEST_FRAMEWORK_LIBRARY}
                       )

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