void pointers

Run-time type identification doesn’t work with void pointers:

//: C08:Voidrtti.cpp

// RTTI & void pointers #include <iostream> #include <typeinfo> using namespace std;

class Stimpy { public:

virtual void happy() {} virtual void joy() {} virtual ~Stimpy() {}

};

int main() {

void* v = new Stimpy; // Error:

//! Stimpy* s = dynamic_cast<Stimpy*>(v); // Error:

//! cout << typeid(*v).name() << endl; } ///:~

A void* truly means “no type information at all.”

Using RTTI with templates

Templates generate many different class names, and sometimes you’d like to print out information about what class you’re in. RTTI provides a convenient way to do this. The following example revisits the code in Chapter XX to print out the order of constructor and destructor calls without using a preprocessor macro:

//: C08:ConstructorOrder.cpp // Order of constructor calls #include <iostream>

#include <typeinfo> using namespace std;

template<int id> class Announce { public:

Announce() {

cout << typeid(*this).name()

Chapter 17: Run-Time Type Identification

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