OpenGL glfwGetVideoMode causes seg fault-CodePudding

I have a simple program where I want to check the formatting of my GLFW window but glfwGetVideoMode causes a segfault.

Here is my code:

        if (!glfwInit()) {
            VI_ERROR("Couldn't init GLFW\n");
            exit(0);
        }

        glfwWindowHint(GLFW_SAMPLES, 6);


        window = glfwCreateWindow(gl_width, gl_height, "GLFW Context", NULL, NULL);

        if (!window) {
            VI_ERROR("Couldn't open window\n");
            exit(0);
        }

        glfwMakeContextCurrent(window);

        gladLoadGL();

        GLFWmonitor* wmonitor = glfwGetWindowMonitor(window);

        glfwGetVideoMode(wmonitor);

Valgrind says this:

==56501== Invalid read of size 8
==56501==    at 0xDF31CB: _glfwPlatformGetVideoMode (in /home/turgut/Desktop/CppProjects/videoo-render/bin/Renderer)
==56501==    by 0xDEDE51: glfwGetVideoMode (in /home/turgut/Desktop/CppProjects/videoo-render/bin/Renderer)
==56501==    by 0x21F8F6: OpenGL::OpenGLRenderer::OpenGLRenderer(int, int, int, int) (OpenGLRenderer.cpp:27)
==56501==    by 0x21BC7A: Application::Run() (Application.cpp:77)
==56501==    by 0x21AB6E: main (main.cpp:18)
==56501==  Address 0x108 is not stack'd, malloc'd or (recently) free'd
==56501== 
==56501== 
==56501== Process terminating with default action of signal 11 (SIGSEGV)
==56501==  Access not within mapped region at address 0x108
==56501==    at 0xDF31CB: _glfwPlatformGetVideoMode (in /home/turgut/Desktop/CppProjects/videoo-render/bin/Renderer)
==56501==    by 0xDEDE51: glfwGetVideoMode (in /home/turgut/Desktop/CppProjects/videoo-render/bin/Renderer)
==56501==    by 0x21F8F6: OpenGL::OpenGLRenderer::OpenGLRenderer(int, int, int, int) (OpenGLRenderer.cpp:27)
==56501==    by 0x21BC7A: Application::Run() (Application.cpp:77)
==56501==    by 0x21AB6E: main (main.cpp:18)
==56501==  If you believe this happened as a result of a stack
==56501==  overflow in your program's main thread (unlikely but
==56501==  possible), you can try to increase the size of the
==56501==  main thread stack using the --main-stacksize= flag.
==56501==  The main thread stack size used in this run was 8388608.

What could I be doing wrong? It's as simple as it gets.

CodePudding user response：

The main problem is that glfwGetWindowMonitor returns null and thus glfwGetVideoMode results in a read from a nullptr.

In GLFW, only fullscreen windows are associated with a monitor. Since you pass NULL as forth parameter to glCreateWindow and never call glfwSetWindowMonitor, the current window is in windowed mode and will not have an associated monitor.