How to properly link libraries with cmake?

Question

I can't get the additional libraries I am working with to link into my project properly.

I am using CLion, which uses cmake to build its projects. I am trying to use several libraries in conjunction with OpenGL to texture some objects. I initially built it in Visual Studio, because I couldn't ever figure out how to get cmake to work with Clion. However, now that the code is all working (in Visual Studio, anyways), I want to be able to use CLion for it, because that is my preferred IDE.

I am still new to cmake, and I don't understand what I am doing wrong with my CMakeLists.txt. Here is what I have:

cmake_minimum_required(VERSION 3.3)
project(texture_mapping)
find_package(OpenGL REQUIRED)
link_directories(${OPENGL_gl_LIBRARY})

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

set(SOURCE_FILES main.cpp camera.h display.h display.cpp mesh.cpp mesh.h obj_loader.cpp obj_loader.h shader.cpp shader.h stb_image.c stb_image.h texture.cpp texture.h transform.h)

link_directories(texture_mapping ${PROJECT_SOURCE_DIR}/lib)

add_executable(texture_mapping ${SOURCE_FILES})

target_include_directories(texture_mapping PUBLIC ${PROJECT_SOURCE_DIR}/include)
target_link_libraries(texture_mapping SDL2 SDL2main SDL2test glew32 glew32s ${OPENGL_gl_LIBRARY})

I tweaked it until it didn't give me any more errors in CLion, but the header files are still not recognized in my code.

Here is the structure of my project:

So, I put all of the libraries I needed, but it doesn't appear to be recognizing them in the code. Clion recognizes them in the project (they aren't appearing red with errors), but when it is built (when I attempt to run it in CLion), I get these errors:

CMakeFiles\texture_mapping.dir/objects.a(mesh.cpp.obj): In function `ZN4MeshD2Ev':
...texture-mapping/mesh.cpp:30: undefined reference to `_imp____glewDeleteVertexArrays'
CMakeFiles\texture_mapping.dir/objects.a(mesh.cpp.obj): In function `ZN4Mesh8InitMeshERK12IndexedModel':
...texture-mapping/mesh.cpp:36: undefined reference to `_imp____glewGenVertexArrays'
...texture-mapping/mesh.cpp:37: undefined reference to `_imp____glewBindVertexArray'
...texture-mapping/mesh.cpp:39: undefined reference to `_imp____glewGenBuffers'
...texture-mapping/mesh.cpp:40: undefined reference to `_imp____glewBindBuffer'
...texture-mapping/mesh.cpp:41: undefined reference to `_imp____glewBufferData'
...texture-mapping/mesh.cpp:43: undefined reference to `_imp____glewEnableVertexAttribArray'
...texture-mapping/mesh.cpp:44: undefined reference to `_imp____glewVertexAttribPointer'
...texture-mapping/mesh.cpp:46: undefined reference to `_imp____glewBindBuffer'
...texture-mapping/mesh.cpp:47: undefined reference to `_imp____glewBufferData'
...texture-mapping/mesh.cpp:49: undefined reference to `_imp____glewEnableVertexAttribArray'
...texture-mapping/mesh.cpp:50: undefined reference to `_imp____glewVertexAttribPointer'
...texture-mapping/mesh.cpp:52: undefined reference to `_imp____glewBindBuffer'
...texture-mapping/mesh.cpp:53: undefined reference to `_imp____glewBufferData'
...texture-mapping/mesh.cpp:55: undefined reference to `_imp____glewBindVertexArray'
...texture-mapping/mesh.cpp:56: undefined reference to `_imp____glewBindVertexArray'
CMakeFiles\texture_mapping.dir/objects.a(mesh.cpp.obj): In function `ZN4Mesh4DrawEv':
...texture-mapping/mesh.cpp:61: undefined reference to `_imp____glewBindVertexArray'
...texture-mapping/mesh.cpp:65: undefined reference to `_imp____glewBindVertexArray'
CMakeFiles\texture_mapping.dir/objects.a(shader.cpp.obj): In function `ZN6ShaderC2ERKSs':
...texture-mapping/shader.cpp:5: undefined reference to `_imp____glewCreateProgram'
...texture-mapping/shader.cpp:11: undefined reference to `_imp____glewAttachShader'
...texture-mapping/shader.cpp:14: undefined reference to `_imp____glewBindAttribLocation'
...texture-mapping/shader.cpp:15: undefined reference to `_imp____glewBindAttribLocation'
...texture-mapping/shader.cpp:17: undefined reference to `_imp____glewLinkProgram'
...texture-mapping/shader.cpp:20: undefined reference to `_imp____glewValidateProgram'
...texture-mapping/shader.cpp:23: undefined reference to `_imp____glewGetUniformLocation'
CMakeFiles\texture_mapping.dir/objects.a(shader.cpp.obj): In function `ZN6Shader4BindEv':
...texture-mapping/shader.cpp:28: undefined reference to `_imp____glewUseProgram'
CMakeFiles\texture_mapping.dir/objects.a(shader.cpp.obj): In function `ZN6Shader6UpdateERK9TransformRK6Camera':
...texture-mapping/shader.cpp:35: undefined reference to `_imp____glewUniformMatrix4fv'
CMakeFiles\texture_mapping.dir/objects.a(shader.cpp.obj): In function `ZN6ShaderD2Ev':
...texture-mapping/shader.cpp:42: undefined reference to `_imp____glewDetachShader'
...texture-mapping/shader.cpp:43: undefined reference to `_imp____glewDeleteShader'
...texture-mapping/shader.cpp:46: undefined reference to `_imp____glewDeleteProgram'
CMakeFiles\texture_mapping.dir/objects.a(shader.cpp.obj): In function `ZN6Shader16CheckShaderErrorEjjbRKSs':
...texture-mapping/shader.cpp:79: undefined reference to `_imp____glewGetProgramiv'
...texture-mapping/shader.cpp:81: undefined reference to `_imp____glewGetShaderiv'
...texture-mapping/shader.cpp:86: undefined reference to `_imp____glewGetProgramInfoLog'
...texture-mapping/shader.cpp:88: undefined reference to `_imp____glewGetShaderInfoLog'
CMakeFiles\texture_mapping.dir/objects.a(shader.cpp.obj): In function `ZN6Shader12CreateShaderERKSsj':
...texture-mapping/shader.cpp:96: undefined reference to `_imp____glewCreateShader'
...texture-mapping/shader.cpp:109: undefined reference to `_imp____glewShaderSource'
...texture-mapping/shader.cpp:110: undefined reference to `_imp____glewCompileShader'
CMakeFiles\texture_mapping.dir/objects.a(texture.cpp.obj): In function `ZN7Texture4BindEj':
...texture-mapping/texture.cpp:36: undefined reference to `_imp____glewActiveTexture'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x24): undefined reference to `SDL_SetMainReady'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x55): undefined reference to `SDL_malloc'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x84): undefined reference to `SDL_wcslen'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0xa5): undefined reference to `SDL_iconv_string'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0xcf): undefined reference to `SDL_free'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0xf4): undefined reference to `SDL_wcslen'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x10f): undefined reference to `SDL_iconv_string'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x143): undefined reference to `SDL_malloc'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x17f): undefined reference to `SDL_free'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x18b): undefined reference to `SDL_free'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x1d6): undefined reference to `SDL_isspace'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x295): undefined reference to `SDL_isspace'
...texture-mapping/lib/SDL2main.lib(./Win32/Release/SDL_windows_main.obj):(.text+0x3a2): undefined reference to `SDL_ShowSimpleMessageBox'

Basically, errors with every usage of SDL and glew, but not glm, which is strange.

What am I doing wrong with my CMakeLists.txt?

Heartfelt

Answer 1

My recommendation is to start simple, and then complicate your project further.

Let me try to explain how linking works in CMake. The idea is that you build modules in CMake, and link them together. Let's ignore header files for now, as they can be all included in your source files.

Say you have file1.cpp, file2.cpp, main.cpp. You add them to your project with:

ADD_LIBRARY(LibsModule 
    file1.cpp
    file2.cpp
)

Now you added them to a module called LibsModule. Keep that in mind. Say you want to link to pthread for example that's already in the system. You can combine it with LibsModule using the command:

target_link_libraries(LibsModule -lpthread)

And if you want to link a static library to that too, you do this:

target_link_libraries(LibsModule liblapack.a)

And if you want to add a directory where any of these libraries are located, you do this:

target_link_libraries(LibsModule -L/home/user/libs/somelibpath/)

Now you add an executable, and you link it with your main file:

ADD_EXECUTABLE(MyProgramExecBlaBla main.cpp)

(I added BlaBla just to make it clear that the name is custom). And then you link LibsModule with your executable module MyProgramExecBlaBla

target_link_libraries(MyProgramExecBlaBla LibsModule)

And this will do it.

What I see in your CMake file is a lot of redundancy. For example, why do you have texture_mapping, which is an executable module in your include directories? So you need to clean this up and follow the simple logic I explained. Hopefully it works.

---

In summary, it looks like this:

project (MyProgramExecBlaBla)  #not sure whether this should be the same name of the executable, but I always see that "convention"
cmake_minimum_required(VERSION 2.8)

ADD_LIBRARY(LibsModule 
    file1.cpp
    file2.cpp
)

target_link_libraries(LibsModule -lpthread)
target_link_libraries(LibsModule liblapack.a)
target_link_libraries(LibsModule -L/home/user/libs/somelibpath/)
ADD_EXECUTABLE(MyProgramExecBlaBla main.cpp)
target_link_libraries(MyProgramExecBlaBla LibsModule)

The most important thing to understand is the module structure, where you create modules and link them all together with your executable. Once this works, you can complicate your project further with more details. Good luck!

---

Note: Keep in mind that this is the simple way to use CMake. The better cross-platform way would be using find_package, which locates a package/library, and provides the libraries and includes in CMake variables so that you could link your program to them. Here's how to do this for boost, for example.

Jaret

How do I create the modules for the external libraries (SDL2, glew, glm) that I am trying to work with? It doesn't seem like I can use add_library() with them. In addition, suppose i have a folder lib/ where the .lib files are stored. If I use target_link_libraries(texture_module -L${PROJECT_SOURCE_DIR}/lib), does that automatically attach all of the *.lib files to that target? – Heartfelt

@CacheStaheli How to link to these specific libraries, I don't know exactly. But once you have the correct way to do it (which has nothing to do with cmake), try to put every one of them in one line, and afterwards after it works experiment putting them all in a single target_link_libraries. And whether everything is automatically added by adding a directory, I highly doubt that. You have to link every library manually. The -L linking only tells the linker where to look for the libraries you specified. – Jaret