C++: Segmentation fault – Calling function through std::vector<> using a virtual function and abstract class – Debian

This may be a total obvious error for some, but I can’t seem to find out why this segmentation fault happens.

I do understand that segmentation faults occur when accessing an address that my program should not access.

First, I have this base-class called "UiObject":

class UiObject {
  private:

  public:
    UiObject();
    virtual void render(char * imageBuffer) = 0;
};

Then, I am deriving multiple other classes from the UiObject class:
For example, the ProgressBar class:

class ProgressBar : public UiObject {
    private:
        int x,y; // Position der ProgressBar auf dem Bildschirm (oben links) (Pixeln)
        int width,height; // Breite und Höhe in Pixeln
    public:
        int maxProgress; // Maximal zu erreichner Fortschritt
        long progress; // Fortschritt aktuell
        ProgressBar(); // Constructor
        void render(char * framebuffer); // Rendermethode
};

Now, these objects are managed and rendered by an UiManager.
The function renderDisplay() is a thread created with std::thread:

void UiManager::renderDisplays() {
  printf("[RENDER] Render thread has been startedn[RENDER] (%x)n", this);
  while(!this->shouldStop) {
    // Removed code that manages the timing of this function (running approximately 60FPS)
  
    // Rendering:

    for(Display d: displayArray) {
      char * framebuffer = d.getFrameBuffer();
      printf("Framebuffer: %xn", framebuffer);
      printf("uiArray: %xn", uiArray);
      printf("&uiArray: %xn", &uiArray);
      for(UiObject* pObject : uiArray) {
        printf("[RENDER] (%x) Rendering Object...", pObject);
        pObject->render(framebuffer);
      } 
      d.renderDisplay();
    }
  }
}

As you can see, for every added Display I am retrieving the framebuffer. I’m opening the /dev/fbX files so i can draw directly onto the screen. This all works fine. d.getFramebuffer() returns a char * pointer so i can manipulate the pixels, which is then passed into the render(char * framebuffer) function of any UiObject.

However, this function call is creating a segfault, and I can’t understand why.
There are sometimes when it works and just runs until the thread should stop, and sometimes it crashes immidiately after the first render-function call.

I add the UiObjects to the UiManager using this:

 ProgressBar pBar;
 pBar.maxProgress = 60*15;
 pBar.progress = 1;

 uiArray.push_back(&pBar);

The UiManager has this as its class-definition:

  class UiManager {
  private:
    char ttyfd; // TTY File Descriptor.
    std::thread uiManagerThread;
    std::chrono::system_clock::time_point timeA;
    std::chrono::system_clock::time_point timeB;
    std::chrono::duration<double, std::milli> work_time;

  public:
    std::vector<Display> displayArray;
    std::vector<UiObject*> uiArray;
    bool shouldStop;
    bool displayFPS;

    UiManager();

    void stop();

    void renderDisplays();

    void addDisplay(Display d);

    void startThread();

    void stopThread();
};

Now I’m wondering why this is.

According to the cppreference https://en.cppreference.com/w/cpp/language/abstract_class and their documentation about abstract classes, I’m not allowed to have the =0; in my UiObject class.
If I remove it, I will get compiler warnings during linking with the message "undefined reference to vtable for UiObject".

What have I done wrong?

I suspect that the std::vector and the for-loop are not quite working in the UiManager.

Im using g++ on debian as my compiler.

My console output:

[RENDER] Render thread has been started
[RENDER] (6ea609f0)
Framebuffer: e09f0010
uiArray: e09eed20
&uiArray: 6ea60a30
./run.sh: Zeile 21: 25018 Speicherzugriffsfehler  ./a.out

It also does not even jump into the ProgressBar render routine. I also commented out the contents of the render-function, therefore i can only suspect that specific function call.