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    <p><code>dynamic_cast</code> can only cast to a pointer value or reference, which is exactly what the error is telling you.</p> <p>From $5.2.7/1 of the C++ Standard.</p> <blockquote> <p>The result of the expression dynamic_cast&lt; T >(v) is the result of converting the expression v to type T. T shall be a pointer or reference to a complete class type, or “pointer to cv void.”</p> </blockquote> <p>In order for <code>dynamic_cast</code> to throw an exception when the object cannot be converted you need to cast to a reference. Change it to the following:</p> <pre><code>dynamic_cast&lt;AA&amp;&gt;(a).aa(); // ^^^ cast to reference. </code></pre> <p>As <a href="https://stackoverflow.com/a/17129771/845568">Johnsyweb</a> pointed out <code>dynamic_cast</code> will always throw <a href="http://en.cppreference.com/w/cpp/types/bad_cast" rel="nofollow noreferrer"><code>std::bad_cast</code></a> when the conversion fails. Although <code>std::bad_cast</code> is derived from <code>std::exception</code> it is always a good idea to use the exception which best fits the expected fail condition. This prevents inadvertently interpreting other errors as an unsuccessful cast.</p> <p>To apply this to your example it might look like the code below.</p> <pre><code>#include &lt;iostream&gt; #include &lt;typeinfo&gt; // std::bad_cast class A { public: virtual void f(void){} }; class AA:public A { public: void aa(void){}; }; int main(void) { A a; try { dynamic_cast&lt;AA&amp;&gt;(a).aa(); } catch(const std::bad_cast&amp; ex) { std::cout &lt;&lt; "["&lt;&lt;ex.what()&lt;&lt;"]" &lt;&lt; std::endl; } return 0; } </code></pre> <p>[Note, doing things like <code>using namespace std;</code> is strongly discouraged as it can cause conflicts with identifiers in the global namespace. I have removed it in the example above.]</p>
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    1. POerror: cannot dynamic_cast ... (target is not pointer or reference)
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    1. COthanks, your explanation is very clear
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    2. COafter modifying my code to <AA&>, the program outputs [std::exception]. how do I get to std::bad_cast? can you please illustrate "it is always a good idea to use the exception which best fits the expected fail condition" using code example? thanks
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    3. CO@focusHard, put a `catch(std::bad_cast& e)` above the existing `catch()` block. And `#include<typeinfo>`.
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