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POPassing a derived-class pointer for a callback
 

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  1. POPassing a derived-class pointer for a callback
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    <p>I'm trying to build a callback-based serial RX driver, and am getting a compile error despite the fact that I'm using a structure which is known good and tested in other applications. I'm sure I'm doing something silly, but for the life of me I can't see it, so a few extra pairs of eyes would be much appreciated.</p> <p>The device should function as follows:</p> <ol> <li>On construction, pass in the comms properties</li> <li>For synchronous communications, do not create a new thread, just block on the TX.</li> <li>For receiving data, spawn a new thread, and execute a callback passed in by the user on RX.</li> </ol> <p>To implement this, I have a base callback class as follows:</p> <pre><code>namespace ocular { Class DeviceCallback { public: DeviceCallback(){} ~DeviceCallback(){} virtual void DeviceCallbackFunction(unsigned char Data){} }; } </code></pre> <p>And the Start Asynch RX method within the device class itself as:</p> <pre><code>void DeviceClass::StartAsynchRX( DeviceCallback* callback ) { m_externalCallback = callback; // Save a local copy of the callback pointer m_started = true; StartAsynchRXThread(); // Spawn the RX Thread return; } </code></pre> <p>I am then deriving my own callback as:</p> <pre><code>Class DemoCallbackClass : public ocular::DeviceCallback { public: void DeviceCallbackFunction(unsigned char myData){ std::cout &lt;&lt; myData; }; } </code></pre> <p>As far as I can tell, this is textbook correct thus-far. This will compile just fine and I can construct, configure and use my device class for synchronous TX. The compile error appears when I attempt to actually start passing the callback pointer in main:</p> <pre><code>void main(void) { DeviceClass MyDevice(); MyDevice.Initialise( *settings from file* ); DemoCallbackClass MyDemoCallback(); MyDevice.StartAsynchRX( &amp;MyDemoCallback ); // ERROR ON THIS LINE } </code></pre> <p>1>......\Src\Support\AR2500 Commissioning\Main.cpp(99): error C2664: 'ocular::DeviceClass::StartAsynchRX' : cannot convert parameter 1 from 'DemoCallbackClass (__cdecl *)(void)' to 'ocular::DeviceCallback *'</p> <p>I'm reasonably sure I've done something silly here, but I can't find it for the life of me. Last week I wrote an event timer class using exactly the same approach and it works just fine. If the structure/approach looks OK to everyone out there, I guess It's a subtle typo, and I just need to rewrite a chunk at a time until I get rid of the damn error.</p> <p>Yours in desparation,</p> <p>DKW</p>
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    1. USOcularProgrammer
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    1. COpossible duplicate of [Why is it an error to use an empty set of brackets to call a constructor with no arguments?](http://stackoverflow.com/questions/180172/why-is-it-an-error-to-use-an-empty-set-of-brackets-to-call-a-constructor-with-no)
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      1. POPassing a derived-class pointer for a callback
      1. USMike Seymour
 

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