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POPolymorphism/inheritance issue with virtual class member function
 

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  1. POPolymorphism/inheritance issue with virtual class member function
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    <p>I might have the wrong idea on exactly what polymorphism versus inheritance is, but basically what I'm trying to do is have <strong><em>classB</em></strong> derive from <strong><em>classA</em></strong>, and create a <strong><em>classB</em></strong> which overrides a pure virtual member function of <strong><em>classA</em></strong>, like so:</p> <p><br/> <strong>classA:</strong></p> <pre><code> ///////////////// // CodeBlock.h // ///////////////// typedef enum { CCBT_UNDEFINED, CCBT_FUNCTION, //... } CODE_BLOCK_TYPE; class CCodeBlock { public: CCodeBlock::CCodeBlock(); CCodeBlock::CCodeBlock(CString&amp; source, DWORD startPos); CCodeBlock::~CCodeBlock(); virtual CODE_BLOCK_TYPE CCodeBlock::GetType() = 0 CString m_code; DWORD m_startPos; DWORD m_length; int m_numLines; } /////////////////// // CodeBlock.cpp // /////////////////// //... CCodeBlock::CCodeBlock(CString&amp; source, DWORD startPos) : m_code(source), m_startPos(startPos) { m_length = m_code.GetLength(); } CODE_BLOCK_TYPE CCodeBlock::GetType() { return CCBT_UNDEFINED; } </code></pre> <p><br/> <strong>classB:</strong></p> <pre><code> ///////////////////// // FunctionBlock.h // ///////////////////// #include "CodeBlock.h" class CFunctionBlock : public CCodeBlock { public: CFunctionBlock::CFunctionBlock(); CFunctionBlock::CFunctionBlock(CString&amp; source, DWORD startPos); CFunctionBlock::~CFunctionBlock(); CODE_BLOCK_TYPE CFunctionBlock::GetType(); } /////////////////////// // FunctionBlock.cpp // /////////////////////// //... CFunctionBlock::CFunctionBlock(CString&amp; source, DWORD startPos) { m_code = source; m_startPos = startPos; } CFunctionBlock::~CFunctionBlock() { CCodeBlock::~CCodeBlock(); } CODE_BLOCK_TYPE CFunctionBlock::GetType() { ////////////////////////////// // &gt;&gt; NEVER GETS CALLED! &lt;&lt; // ////////////////////////////// return CCBT_FUNCTION; } </code></pre> <p><br/> <strong>main:</strong></p> <pre><code>CCodeBlock *block = new CFunctionBlock(L"function hello(){ print('hello') }", iPos) CODE_BLOCK_TYPE type = block-&gt;GetType(); // ALWAYS RETURNS CCBT_UNDEFINED! </code></pre> <p><br/> As you can see, <strong><em>GetType()</em></strong> always returns <I>CCBT_UNDEFINED</I>. Keep in mind that CCodeBlock is meant to be a 'generic' version of CFunctionBlock (as well as a few other like-minded classes, some of which contain a CCodeBlock 'm_parent' member variable), and is supposed to inherit any CCodeBlock member variables &amp; member functions, as well as override a specific list of functions contained in CCodeBlock.</p> <p>How can this be achieved? Would I need to resort to using templates (if that's even possible)?</p>
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    1. CObtw, you don't need `CCodeBlock::` when you declare member functions inside class `CCodeBlock`
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    2. COAlso, the types don't match. `CCodeBlock CFunctionBlock::GetType()` vs `CODE_BLOCK_TYPE CCodeBlock::GetType()`. Does this code even compile?
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    3. CO@billz that was a copy/paste typo, with an exception to CFunctionBlock::GetType() -- which seems to have been the issue all along. After removing 'CFunctionBlock::', block->GetType() now returns CCBT_FUNCTION. So thanks for that! If you post this as the answer, I will credit it for you.
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