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copied!<p>Or you can use typeid, which might be faster than dynamic_cast (also with dynamic_cast you can cast to intermediary types in the hierarchy).</p> <p>It looks rather bad:</p> <pre><code>#include <iostream> #include <typeinfo> class Creature { char x[4]; public: virtual ~Creature() {} }; class Animal: public Creature { char x[8];}; class Bird: public Creature { char x[16]; }; class Dog: public Animal { char x[32]; }; class Cat: public Animal { char x[64]; }; class Parrot: public Bird { char x[128]; }; unsigned creature_size(const Creature& cr) { if (typeid(cr) == typeid(Animal)) { return sizeof (Animal); } else if (typeid(cr) == typeid(Dog)) { return sizeof(Dog); } else if (typeid(cr) == typeid(Cat)) { return sizeof(Cat); } else if (typeid(cr) == typeid(Bird)) { return sizeof(Bird); } else if (typeid(cr) == typeid(Parrot)) { return sizeof(Parrot); } else if (typeid(cr) == typeid(Creature)){ return sizeof(Creature); } assert(false && "creature_size not implemented for this type"); return 0; } int main() { std::cout << creature_size(Creature()) << '\n' << creature_size(Animal()) << '\n' << creature_size(Bird()) << '\n' << creature_size(Dog()) << '\n' << creature_size(Cat()) << '\n' << creature_size(Parrot()) << '\n' ; } </code></pre> <p>For each new type you'll need to add code to the creature_size function. With a virtual size function you'll need to implement this function in each class as well. However, this function will be significantly simpler (perfectly copy-n-pasteable, which shows there might be both a limitation in the language and a problem with your code design):</p> <pre><code>virtual unsigned size() const { return sizeof(*this); } </code></pre> <p>And you can make it abstract in the base class which means that it will be a compiler error if you forget to override this method.</p> <p>Edit: this is naturally assuming that given any Creature you want to know its size. If you have a strong reason to believe that you are dealing with a Dog - or a subclass of Dog (and you don't care if it is a subclass), then naturally you can use dynamic_cast for an <em>ad hoc</em> test.</p>

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