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Nene

Dynamic_cast in constructor. Please

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Hi everyone, I have a problem with the following dynamic_cast (it returns 0): template<class T> class Base { public: Base(){ T* t = dynamic_cast<T*>(this); } virtual ~Base(){} }; class Derived : public Base<Derived>{ public: Derived():Base(){} void g(){} }; int main() { Derived d; } Any suggestion? Thanks a lot!!! :)

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During Base::Base(), derived classes aren't constructed yet. It would be unsafe to access their members or member functions.

Consider:

template<class T>
class Base
{
Base()
{
T *self = dynamic_cast<T*>(this);

self->frobnicate();
}
}

class Derived : public Base<Derived>
{
void frobnicate()
{
// manipulate member.
}

std::string member;
};


If the dynamic_cast returned a pointer, and we call frobnicate on it, the code would probably crash at run time. That is a best case scenario - it could also silently corrupt unrelated memory, creating a debugging nightmare.

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Also, CRTP.

Note that template specialization is resolved at compile-time. But it is still not safe to use Derived's functions in constructor.

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