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POVirtual Calls using address of pure virtual member. Is it legal?
 

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    <p>I read sometime back (probably on c.l.c++.moderated) that virtual function calls can be templatized. I tried something on the following lines.</p> <pre><code>#include &lt;iostream&gt; template&lt;class T, class FUN&gt; void callVirtual(T&amp; t, FUN f){ (*t.*f)(); } struct Base{ virtual ~Base(){} virtual void sayHi()=0; }; struct Derived : public Base{ void sayHi(){ std::cout &lt;&lt; "Hi!" &lt;&lt; std::endl; } }; void Test(){ Base* ptr = new Derived; callVirtual(ptr,&amp;Base::sayHi); } int main() { Test(); return 0; } Output: Hi! </code></pre> <p>The templatized method though given the address of pure virtual base member method at compile time calls the correct method at runtime. Is it legal in standard C++ to take address of a pure virtual member?</p> <p>Thanks in advance</p> <p><strong>EDIT-1:</strong> I removed the second part of the question 'how does it work?'. Looks like that is what is catching attention.</p> <p><strong>EDIT-2:</strong> I searched c.l.c++.moderated and came across this <a href="http://groups.google.com/group/comp.lang.c++.moderated/browse_thread/thread/5ddde8cf1ae59a0d" rel="nofollow noreferrer">link</a> (<a href="http://groups.google.com/group/comp.lang.c++.moderated/browse_thread/thread/5ddde8cf1ae59a0d" rel="nofollow noreferrer">http://groups.google.com/group/comp.lang.c++.moderated/browse_thread/thread/5ddde8cf1ae59a0d</a>). The consensus seems like since the standard does not restrict it, it is vaild.</p> <p><strong>EDIT-3:</strong> After reading the codeproject article (thanks to ovanes), i am thinking that the compilers do some magic. Since virtual functions are implemented via vtable (which is compiler specific), taking address of a virtual function always gives the offset in the vtable. Depending on the 'this' pointer used, the appropriate function (whose address is at the offset) is called. I am not sure how to vindicate this though as the standard does not say anything abt it!</p>
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