Clion (cmake) won't link the libraries

Question

I'm having a problem when trying to link SDL2 and GL libraries to Clion (cmake). Despite changing the cmakelists.txt and adding the target-link-libraries() function. So the cmake file looked like this:

cmake_minimum_required(VERSION 3.9)
project(OpenGL1)

set(CMAKE_CXX_STANDARD 17)

target_link_libraries(OpenGL1 SDL2 GL)

add_executable(OpenGL1 main.cpp Display1.cpp Display1.h)

But with no luck. Clion would not link the libraries with errors such as undifined refference to functions of the libraries.

Then a friend suggested it that I would wite that into cmakelists file:

cmake_minimum_required(VERSION 3.9)
project(OpenGL1)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -lGL -lSDL2 -lOpenGL")


add_executable(OpenGL1 main.cpp Display1.cpp Display1.h)

And it kinda worked... But it would not find the -lOpenGL. Last but not least, my project will not compile with the traditional way in the terminal with g++. And it will compile fine with one .cpp file. My project consists of 2 cpp files and a header file. Like that:

• main.cpp
• Display1.cpp
• Display.h

And code of the files is the following:

1. main.cpp

   #include <iostream>
   #include "Display.h"
   
   using namespace std;
   
   int main() {
       Display d1(800,600,"Hello");
   
       while (!d1.m_isClosed()){
           d1.Clear(0.0f, 0.15f, 0.3f, 1.0f);
           d1.Update();
       }
       return 0;
   }
   

2. Display1.cpp

   #include "Display.h"
   #include <GL/glew.h>
   
   using namespace std;
   
   Display::Display(int width, int height, const string title) {
       SDL_Init(SDL_INIT_EVERYTHING);
       SDL_GL_SetAttribute(SDL_GL_RED_SIZE,8);
       SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE,8);
       SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE,8);
       SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE,8);
       SDL_GL_SetAttribute(SDL_GL_BUFFER_SIZE,32);
       SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER,1);
   
       m_window = SDL_CreateWindow(title.c_str(),SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,width,height,SDL_WINDOW_OPENGL);
       m_glContext = SDL_GL_CreateContext(m_window);
   
       GLenum status = glewInit();
       if (status != GLEW_OK)
           cerr << "Glew failed!" << endl;
   
       isClosed = false;
   }
   
   Display::~Display() {
       SDL_GL_DeleteContext(m_glContext);
       SDL_DestroyWindow(m_window);
       SDL_Quit();
   }
   
   void Display::Clear(float r, float g, float b, float a) {
       glClearColor(r,g,b,a);
       glClear(GL_COLOR_BUFFER_BIT);
   }
   
   bool Display::m_isClosed() {
       return isClosed;
   }
   
   void Display::Update() {
       SDL_GL_SwapWindow(m_window);
   
       SDL_Event e;
       while (SDL_PollEvent(&e)){
           if (e.type == SDL_QUIT)
               isClosed = true;
       }
   }
   

3. Display1.h

    #ifndef OPENGL_DISPLAY_H
    #define OPENGL_DISPLAY_H
   
    #include <iostream>
    #include <SDL2/SDL.h>
   
    using namespace std;
   
   
    class Display {
     SDL_Window* m_window;
     SDL_GLContext m_glContext;
     bool isClosed;
    public:
      Display(int width, int height, string title);
      virtual ~Display();
      void Update();
      bool m_isClosed();
      void Clear(float r, float g, float b, float a);
   };
   
   
   #endif //OPENGL_DISPLAY_H
   

Now, i know that others have asked the same, but nothing could help me so that's why I'm asking. I'm running Ubuntu 17.10 (64-bit). Thanks in advance!

Answer 1

You have to fix your CMakeLists.txt:

cmake_minimum_required(VERSION 3.9)
project(OpenGL1)

set(CMAKE_CXX_STANDARD 17)

find_package(OpenGL REQUIRED)
find_package(GLEW REQUIRED)

set(SDL2_INCLUDE_DIRS /usr/include/SDL2)
set(SDL2_LIBRARIES /usr/lib/x86_64-linux-gnu/libSDL2.so)

include_directories(${OPENGL_INCLUDE_DIRS} ${GLEW_INCLUDE_DIRS} ${SDL2_INCLUDE_DIRS})

add_executable(OpenGL1 main.cpp Display1.cpp Display1.h)

target_link_libraries(OpenGL1 ${OPENGL_LIBRARIES} ${GLEW_LIBRARIES} ${SDL2_LIBRARIES})

First find the OpenGL files with find_package(OpenGL REQUIRED). Then set the paths for SDL2. Set the include directories for your target (OpenGL1). Add your target. Link libraries to your target.

A better way to use SDL2 is to use FindSDL2.cmake and add find_package(SDL2) to your CMakeLists.txt:

cmake_minimum_required(VERSION 3.9)
project(OpenGL1)

set(CMAKE_CXX_STANDARD 17)

find_package(OpenGL REQUIRED)
find_package(GLEW REQUIRED)
find_package(SDL2 REQUIRED)

include_directories(${OPENGL_INCLUDE_DIRS} ${GLEW_INCLUDE_DIRS} ${SDL2_INCLUDE_DIRS})

add_executable(OpenGL1 main.cpp Display1.cpp Display1.h)

target_link_libraries(OpenGL1 ${OPENGL_LIBRARIES} ${GLEW_LIBRARIES} ${SDL2_LIBRARIES})

SDL2 installs its own cmake configuration file called sdl2-config.cmake, so you don't need to download it from github.