Which casting technique is better for doing casting from upper class to lower class in C++

i want to cast from upper class pointer to lower class i.e from the base class pointer to derived class pointer.

Should i use "Dynamic_cast" or "rein开发者_开发问答terpret_cast"? please advice me

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Don't use reinterpret_cast - either use static_cast or dynamic_cast. If you're sure that the pointer is to exactly that derived class object use static_cast, otherwise use dynamic_cast (that will require the base class to be polymorhic) and check the result to ensure that the pointer is indeed to the class you want.

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It depends on what you know about the pointer.

If you know for sure that the pointer you have is of a child type, you can static_cast<> it safely.

If you don't know for sure, just go with dynamic_cast<> but this has a cost and is slower.

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reinterpret_cast<> is a last resort and should be avoided.

In Qt, if casting between QObjects, use qobject_cast<>. It's semantically like dynamic_cast but has no issues with dll boundaries etc.

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To add to Ereon's answer: And if you do not know the type use dynamic_cast to do a run time type check by catching the bad_cast exception.