Typeid

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In C++, the typeid keyword is used to determine the class of an object at runtime. According to the C++ specification, it returns a reference to typeinfo. As such, modern compilers will not let you assign the return value of typeid to a local variable, as the constructor for typeinfo is private. Using the name member function of typeinfo is a sufficient general workaround for situations which require one to store the class type. typeid is often preferred to dynamic_cast<class_type> in situations where just the class information is needed, because typeid is a constant-time procedure, whereas dynamic_cast must traverse the class derivation lattice of its argument at runtime.

Examples

Supposing that you had class "Message" a derived class "FatMessage":...

class Message ;

class FatMessage : public Message ;

..., and the following code:

Message *n = new Message();
Message *p = new FatMessage();
string wakka = typeid(*n).name();

cout << typeid(*p) << endl;
cout << typeid(p) << endl;
cout << wakka << endl;

Then, typeid would return the following results in code compiled with RTTI:

FatMessage
Message
Message

Important: Note that you had to dereference the pointer in the first cout.

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