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    <ol> <li><code>NULL-&gt;derivedspecific()</code> won't compile</li> <li><code>((derived*)NULL)-&gt;derivedspecific()</code> is undefined behaviour (segmentation fault on most platforms</li> </ol> <p>there is a mechanism which is specifically designed to support this kind of behaviour, i.e. <code>dynamic_cast</code> which goes like:</p> <pre><code>#include &lt;typeinfo&gt; class base { public: virtual ~base(){}; }; class derived1 : public base { public: void derived1specific() const {} }; class derived2 : public base { public: void derived2specific() const {} }; int main() { // use pointers base* test = new derived1; derived2* d2 = dynamic_cast&lt;derived2*&gt;(test); if(d2) d2-&gt;derived2specific(); derived1* d1 = dynamic_cast&lt;derived1*&gt;(test); if(d1) d1-&gt;derived1specific(); // or simply if(derived1* d1 = dynamic_cast&lt;derived1*&gt;(test) ) d1-&gt;derived1specific(); else if(derived2* d2 = dynamic_cast&lt;derived2*&gt;(test)) d2-&gt;derived2specific(); // use references const base&amp; testr = derived1(); try{ const derived1&amp; d1 = dynamic_cast&lt;const derived1&amp;&gt;(testr); d1.derived1specific(); } catch(std::bad_cast&amp;){} try{ const derived2&amp; d2 = dynamic_cast&lt;const derived2&amp;&gt;(testr); d2.derived2specific(); } catch(std::bad_cast&amp;){} } </code></pre> <p>What you wanted to do, which I would not recommend you, is something like:</p> <pre><code>auto doNothing = [](){return;}; (test-&gt;type()==1?(((derived1*)test)-&gt;derived1specific()):doNothing()); </code></pre> <p>You can try the full code <a href="http://coliru.stacked-crooked.com/view?id=357c3c8e2e9fe23bf1a4d5c6a55f7ff4-72f1b4de714fd92d7b53b2e51b310d82" rel="nofollow">here</a>.</p> <p>As for your comment: you can substitute the macro with a free-function (which is advisable anyway)</p> <pre><code>void derived1specific(base* b){ if(derived1* d1 = dynamic_cast&lt;derived1*&gt;(b)) d1-&gt;derived1specific(); } </code></pre> <p>which does exactly what your code wants to do: execute the derived specific function if and only if it is appropriate; you simply call it like:</p> <pre><code>derived1specific(test); </code></pre>
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    1. USStefano Falasca
    1. USStefano Falasca
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      1. VTUpMod
    1. COYeah it's nice but imagine i have hundreds of these derives. I have to write this down every time when i want to use its members/methods. Second thing i thought is using templates but it wont work because they are working at compile time.
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      1. USDaniel Adamko
    2. COYou wouldn't need to write it every time, you can use a free-function, pretty much as you would have used the macro. Using the function is better anyway!
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      1. USStefano Falasca
 

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