Cmake linking to shared library cannot find library

Question

On Ubuntu, I have two directories: build and src. In src, my CMakeLists.txt file has the lines:

add_executable(Test main.cpp)

target_link_libraries(Test libCamera.so)

After running cmake in the build directory (cmake ../src), I then copy my library file libCamera.so into the build directory. After running make, the main.cpp.o file compiles successfully, but I receive the following error during linking:

/usr/bin/ld: cannot find -lCamera

Why is this? The shared library is in the same directory that I am building in... and the same thing happens if I copy the library to /usr/bin...

Solution

You should not put prefix lib and suffix .so of the library, so just use:

target_link_libraries(Test Camera)

if your library not found you may need to add directory, where library is located:

link_directories( /home/user/blah ) # for specific path
link_directories( ${CMAKE_CURRENT_BINARY_DIR} ) # if you put library where binary is generated

Note: you copied lib to /usr/bin but unlike Windows where dll files stored with executables, in Linux that is not the case, so it would be /usr/lib, not /usr/bin. Also you may change LD_LIBRARY_PATH variable to make your program to find a library in a custom location.

Comments

[Karnivaurus]

If I do that, then I get the same error message as before: Linking CXX executable Test, /usr/bin/ld: cannot find -lCamera

[Karnivaurus]

I have added the line link_directories(/home/karnivaurus/Projects/Test/build) to my CMakeLists.txt file, but I still get the same error.... However, if I copy the library to /usr/lib, as you suggested, it compiles fine.... Any idea why the first attempt did not solve it?

[Slava]

@Karnivaurus btw for build you should use cmake var as mentioned above, but full path should still work. Why it does not is difficult to say without looking into actual CMakeLists.txt

[Slava]

@Karnivaurus note that binary is being buit and linked in build/src subdirectory. If you put lib there you may not need to add that dir. But normally you should not copy library there but use find_library() instead