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POC++ virtual function undefined at link time - why?
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  1. POC++ virtual function undefined at link time - why?
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    copied!<p>I'm having a bit of trouble using virtual functions in C++, and I might be misusing them in a constructor. The problem is that when linking a component lib (written by me) into my final executable, a virtual function is marked as undefined, even though I have written an implementation for it, and linked it.</p> <p>I have the following class:</p> <pre><code>template&lt;class BufferType, class ConnectionType, class HandlerType&gt; class UdpConnection { public: UdpConnection(size_t dispatchCount) : service(), listener(service), pool(dispatchCount), sysMsgHandlers(), bufferPool(), buffers() { assert(dispatchCount &gt; 0); initBuffers(dispatchCount); initSysHandlers(); } protected: virtual void initSysHandlers() = 0; } </code></pre> <p>In my subclass:</p> <pre><code>class UdpClient : public UdpConnection&lt;SyncBufferHandler, UdpClient, ClientNetworkHandler&gt; { protected: void initSysHandlers(); } </code></pre> <p>And the subclass source file:</p> <pre><code>void UdpClient::initSysHandlers() { } </code></pre> <p>As you can see, I am calling a virtual function in my constructor. As far as I can tell, this should be fine, since I am aware that my subclass constructor won't have been called, so I can't use any instance variables, but I simply add a few sub-class specific items to a std::map. </p> <pre><code>Linking CXX static library libnetwork.a [ 75%] Built target network Scanning dependencies of target testclient [ 87%] Building CXX object CMakeFiles/testclient.dir/src/test/testclient.cpp.o Linking CXX executable testclient src/network/libnetwork.a(udpclient.cpp.o): In function `voip::network::UdpConnection&lt;voip::network::client::SyncBufferHandler, voip::network::client::UdpClient, voip::network::client::ClientNetworkHandler&gt;::UdpConnection(unsigned long)': udpclient.cpp:(.text._ZN4voip7network13UdpConnectionINS0_6client17SyncBufferHandlerENS2_9UdpClientENS2_20ClientNetworkHandlerEEC2Em[voip::network::UdpConnection&lt;voip::network::client::SyncBufferHandler, voip::network::client::UdpClient, voip::network::client::ClientNetworkHandler&gt;::UdpConnection(unsigned long)]+0x10d): undefined reference to `voip::network::UdpConnection&lt;voip::network::client::SyncBufferHandler, voip::network::client::UdpClient, voip::network::client::ClientNetworkHandler&gt;::initSysHandlers()' collect2: ld returned 1 exit status </code></pre> <p>What am I doing wrong here? Please ask if you need more information, wanted to keep it as short as possible!</p>
 

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