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POc++ calling a non static function from a static function
 

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  1. POc++ calling a non static function from a static function
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    <p>I'm experiencing an access violation error when I try to call non static function.</p> <p>my <code>.h</code> file looks like this.</p> <pre><code>class World { public: World(); virtual ~World(); static void CALLBACK DispatchCallback( SIMCONNECT_RECV *pData, DWORD cbData, void *pContext ); void Process(SIMCONNECT_RECV *pData, DWORD cbData); virtual void frameEvent(); virtual void init(); }; </code></pre> <p>Now in my .cpp file the init() function I call a function that return data to my callback function.</p> <pre><code>SimConnect_CallDispatch(hSimConnect, DispatchCallback, NULL); </code></pre> <p>Which sends data to the <code>DisPatchCallback</code> function.</p> <p>In this function the following code resides:</p> <pre><code>void CALLBACK World::DispatchCallback( SIMCONNECT_RECV *pData, DWORD cbData, void *pContext) { World *pThis = reinterpret_cast&lt;World*&gt;(pContext); pThis-&gt;Process(pData, cbData); } </code></pre> <p>this function is a static function which creates a World object to call the Process function.</p> <p>This works but it break on the line where it wants to access the frameEvent function.</p> <pre><code>void World::Process(SIMCONNECT_RECV *pData, DWORD cbData) { HRESULT hr; switch(pData-&gt;dwID) { case SIMCONNECT_RECV_ID_EVENT_FRAME: frameEvent(); //it breaks here frameEvent is a non static function break; } } </code></pre> <blockquote> <p>Access violation reading location 0x00000000.</p> </blockquote> <p>Can someone point me to the right direction as to solve this issue.?</p> <p>If you wonder I'm writing a plugin for Microsoft Flight Simulator X.</p> <p>I'm trying to implement <code>simconnect.h</code> in a oo way. Msdn shows an example that I'm trying to implement.</p> <pre><code>class CName { void Dispatch(); static void DispatchCallback( SIMCONNECT_RECV *pData, DWORD cbData, void *pContext ); void Process(SIMCONNECT_RECV *pData, DWORD cbData); HANDLE hSimConnect; // use SimConnect_Open to set this value. }; void CName::Dispatch() { ::SimConnect_Dispatch(hSimConnect, &amp;CName;::DispatchCallback, this); } // static function void CName::DispatchCallback( SIMCONNECT_RECV *pData, DWORD cbData, void *pContext) { CName *pThis = reinterpret_cast&lt;CName*&gt;(pContext); pThis-&gt;Process(pData, cbData); } void CName::Process(SIMCONNECT_RECV *pData, DWORD cbData) { // do processing of SimConnect data } </code></pre> <p>I hope I gave enough information.</p>
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    1. COWhat are you trying to achieve with static functions with context? And, in general, using `casts` in such a way indicates bad desing...
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      1. USGriwes
    2. CO@Griwes: This is actually a very common pattern when writing C++ code with C APIs -- you pass in `this` as a context parameter along with a `static` callback function, which forwards the callback into a class method on the object. It's used with window procedures, thread procedures, library callbacks, etc.
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