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POWeird polymorphism behavior with multiple inheritance in C++?
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  1. POWeird polymorphism behavior with multiple inheritance in C++?
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    copied!<p>So, I'm writing on a little Pong game clone using SDL and I have the following setup.</p> <p>There's a general game class <code>SlimGame</code> which inherits from an FSM class and an event handler class:</p> <pre><code>// DEFINITION class SlimGame : public SlimFSM, public SlimEventHandler { protected: bool running; // indicates if the game is running public: bool isRunning() { return this-&gt;running; } void setRunning(bool r) { this-&gt;running = r; } void run(); // encapsulates the game loop }; // IMPLEMENTATION void SlimGame::run() { SDL_Event event; this-&gt;setRunning(true); while(this-&gt;isRunning()) { while(SDL_PollEvent(&amp;event)) { this-&gt;handleEvent(&amp;event); std::cout &lt;&lt; "MAIN LOOP Running: " &lt;&lt; this-&gt;isRunning(); &lt;&lt; endl; } // ... } } </code></pre> <p>The FSM class is irrelevant to the weird behavior, but the event handler class looks like this:</p> <pre><code>// DEFINITION class SlimEventHandler { public: SlimEventHandler() { } virtual ~SlimEventHandler() { } void handleEvent(SDL_Event *event); virtual void onExit(); }; // IMPLEMENTATION void SlimEventHandler::handleEvent(SDL_Event *event) { switch(event-&gt;type) { case SDL_QUIT: this-&gt;onExit(); break; } } void SlimEventHandler::onExit() { std::cout &lt;&lt; "PARENT onExit!" &lt;&lt; std::endl; } </code></pre> <p>And then I have my <code>PongGame</code> class itself which inherits from <code>SlimGame</code> (and therefore indirectly from <code>SlimFSM</code> and <code>SlimEventHandler</code>):</p> <pre><code>// DEFINITION class PongGame : public SlimGame { public: PongGame(); ~PongGame(); void onExit(); }; // IMPLEMENTATION void PongGame::onExit() { this-&gt;setRunning(false); std::cout &lt;&lt; "CHILD onExit!" &lt;&lt; std::endl; } </code></pre> <p>So with this setup I run my game like this and it starts up, nicely:</p> <pre><code>int main(int argc, char **argv) { PongGame game; // setup game.run(); // tear down return 0; } </code></pre> <p>However the event handling doesn't work the way it's supposed to work. If I click the window closing button the <code>SDL_QUIT</code> event get's fired and the method <code>handleEvent</code> gets called. This is fine, but the method itself calls <code>onExit</code> of its own, not the inherited method of the <code>PongGame</code> class, so I see:</p> <pre><code>PARENT onExit! </code></pre> <p>in the console instead of</p> <pre><code>CHILD onExit! </code></pre> <p>Shouldn't the derived method in <code>PongGame</code> be called, instead of the virtual empty implementation in <code>SlimEventHandler</code>?</p>
 

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