Does dynamic cast require RTTI?

Does dynamic cast require RTTI?

The fact, that the cast is safe is known by the compiler at compile time. This means, that dynamic_cast does not need to use RTTI. We can say in general, that dynamic_cast is a tool for moving around the inheritance tree – up and down.

Is dynamic cast bad?

dynamic_cast is “bad design” for the simple reason that it violates this purpose, since you need your object to be of some derived type, so it doesn’t suffice to know the base type of it. That being said it still has its use (especially as the world isn’t as simple as Java likes it to be).

When should I use dynamic pointer cast?

dynamic_cast is exclusively used for handling polymorphism. You can cast a pointer or reference to any polymorphic type to any other class type (a polymorphic type has at least one virtual function, declared or inherited).

Why do we need RTTI?

RTTI, Run-Time Type Information, introduces a [mild] form of reflection for C++. It allows to know for example the type of a super class, hence allowing to handle an heterogeneous collection of objects which are all derived from the same base type. in ways that are specific to the individual super-classes.

Why is RTTI bad?

RTTI only works if your classes have a virtual table. If you have a virtual table you can implement virtual functions. The reason you should use virtual functions over a switch on the type of the object is that it works better with inheritance chains, and is less fragile when adding new classes.

Why do we use dynamic cast conversion?

Dynamic Cast: A cast is an operator that converts data from one type to another type. In C++, dynamic casting is mainly used for safe downcasting at run time. A dynamic_cast works only polymorphic base class because it uses this information to decide safe downcasting.

Is dynamic cast expensive?

dynamic_cast costs a lot. A simple call can use 100-200 cycles under Visual C++. Calling a virtual function (or checking a base-class member) and testing the result can run up to 20x faster.

How do I stop dynamic casting?

pattern to avoid dynamic_cast

1. Use dynamic_cast to analyze subclass. Not good, too slow as I make calls very often and on limited hardware.
2. Use a flag in each subclass, like an enum {IS_SUBCLASS_B, IS_SUBCLASS_C}. Not good as it doesnt feel OO.
3. Also put the classes in other vectors, each for their specific task.

What happens if dynamic cast fails?

When we try to dynamic_cast that to a Derived, it will fail, because the conversion can’t be made. If a dynamic_cast fails, the result of the conversion will be a null pointer.

Can you dynamic cast a reference?

The dynamic_cast operator can be used to cast to reference types. C++ reference casts are similar to pointer casts: they can be used to cast from references to base class objects to references to derived class objects.

Is Typeid a runtime?

Since typeid is applied to a type rather than an object, there is no runtime type information, so that overhead won’t be a problem.

At which time does the Static_cast can be applied?

Explanation: Static_cast can be applied to only compile-time construct and not during run time construct.

Why do I use-FNO-RTTI in C + +?

Perhaps you might like to elaborate on why you are using -fno-rtti. Disable generation of information about every class with virtual functions for use by the C++ runtime type identification features ( dynamic_cast and typeid ). If you don’t use those parts of the language, you can save some space by using this flag.

When to use the dynamic _ cast operator in GCC?

Note that exception handling uses the same information, but it will generate it as needed. The dynamic_cast operator can still be used for casts that do not require runtime type information, i.e. casts to void * or to unambiguous base classes.

Can a virtual function be compiled without RTTI?

There is discussion about the relationship between virtual functions and RTTI available at No RTTI but still virtual methods. The short version is that virtual functions should be fine without RTTI. Thanks for contributing an answer to Stack Overflow!