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    <p>I think <strong>it is an optimisation</strong>! A little known and rarely (you could say "never") used feature of <code>typeid</code> is that a null dereference of the argument of <code>typeid</code> throws an exception instead of the usual UB.</p> <blockquote> <p>What? Are you serious? Are you drunk?</p> </blockquote> <p>Indeed. Yes. No.</p> <pre> int *p = 0; *p; // UB typeid (*p); // throws </pre> <p>Yes, this is ugly, even by the C++ standard of language ugliness.</p> <p>OTOH, this does not work anywhere <strong>inside</strong> the argument of <code>typeid</code>, so adding any clutter will cancel this "feature":</p> <pre> int *p = 0; typeid(1 ? *p : *p); // UB typeid(identity(*p)); // UB </pre> <p>For the record: I am not claiming in this message that automatic checking by the compiler that a pointer is not null before doing a dereference is necessarily a crazy thing. I am only saying that doing this check when the dereference is the immediate argument of <code>typeid</code>, <strong>and not elsewhere</strong>, is totally crazy. (Maybe is was a prank inserted in some draft, and never removed.)</p> <p>For the record: I am not claiming in the previous "For the record" that it makes sense for the compiler to insert automatic checks that a pointer is not null, and to to throw an exception (as in Java) when a null is dereferenced: in general, throwing an exception on a null dereference is absurd. This is a programming error so an exception will not help. An assertion failure is called for.</p>
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    1. POWeird use of `?:` in `typeid` code
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    1. COWhat? Are you serious? Are you drunk?
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      1. USMateen Ulhaq
    2. CO+100 Nice catch!
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      1. USChristian Rau
    3. CO+1, this is the solution.
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      1. USJohannes Schaub - litb
 

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