Does C have RTTI?

Does C have RTTI?

In computer programming, run-time type information or run-time type identification (RTTI) is a feature of some programming languages (such as C++, Object Pascal, and Ada) that exposes information about an object’s data type at runtime.

What is RTTI in CPP?

In C++ the RTTI is a mechanism, that exposes information about an object’s datatype during runtime. This feature can be available only when the class has at least one virtual function. It allows the type of an object to be determined when the program is executing.

How expensive is RTTI?

A while ago I measured the time costs for RTTI in the specific cases of MSVC and GCC for a 3ghz PowerPC. In the tests I ran (a fairly large C++ app with a deep class tree), each dynamic_cast<> cost between 0.8μs and 2μs, depending on whether it hit or missed.

What is RTTI used for?

Run-time type information (RTTI) is a mechanism that allows the type of an object to be determined during program execution. RTTI was added to the C++ language because many vendors of class libraries were implementing this functionality themselves. This caused incompatibilities between libraries.

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.

Is Typeid slow?

typeid() can be much faster than other type checks if all the stars are aligned, or it can be extremely slow. typeid() requires the compiler to determine if a pointer is null, so if you already know your pointer is non-null, it’s more efficient to use typeid() on a reference instead.

What is RTTI in oops?

In C++, RTTI (Run-time type information) is a mechanism that exposes information about an object’s data type at runtime and is available only for the classes which have at least one virtual function. It allows the type of an object to be determined during program execution.

Which type of class we can apply RTTI?

3. To which type of class, We can apply RTTI? Explanation: RTTI is available only for classes which are polymorphic, which means they have at least one virtual method.

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.

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.

Does dynamic_cast use RTTI?

RTTI (Run-time type Information) in C++ For example, dynamic_cast uses RTTI and following program fails with error “cannot dynamic_cast `b’ (of type `class B*’) to type `class D*’ (source type is not polymorphic) ” because there is no virtual function in the base class B.

What does Typeid return?

The typeid operator returns an lvalue of type const std::type_info that represents the type of expression expr. You must include the standard template library header to use the typeid operator. Classes A and B are polymorphic; classes C and D are not.

When to use the RTTI feature in C + +?

In C++ the RTTI is a mechanism, that exposes information about an object’s datatype during runtime. This feature can be available only when the class has at least one virtual function. It allows the type of an object to be determined when the program is executing.

What happens if you turn off RTTI in C?

If your compiler lets you totally turn off RTTI, the final resulting code size savings can be significant though, with such a small RAM space. The compiler needs to generate a type_info structure for every single class with a virtual function. If you turn off RTTI, all these structures do not need to be included in the executable image.

How many bytes does RTTI hold in GCC?

From what I can make out, the RTTI structures used by GCC (these are all the subclasses of std::type_info) only hold a few bytes for each type, aside from the name. It isn’t clear to me whether the names are present in the output code even with -fno-rtti.

How does RTTI affect the size of a binary?

Either way, the change in size of the compiled binary should reflect the change in runtime memory usage. A quick experiment (using GCC 4.4.3 on Ubuntu 10.04 64-bit) shows that -fno-rtti actually increases the binary size of a simple test program by a few hundred bytes. This happens consistently across combinations of -g and -O3.

Does C have RTTI? In computer programming, run-time type information or run-time type identification (RTTI) is a feature of some programming languages (such as C++, Object Pascal, and Ada) that exposes information about an object’s data type at runtime. What is RTTI in CPP? In C++ the RTTI is a mechanism, that exposes information about…