Type Casting Part II

const_cast

This type of casting manipulates the constness of an object, either to be set or to be removed. For example, in order to pass a const argument to a function that expects a non-constant parameter:

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// const_cast
#include
using namespace std;

void print (char * str)
{
cout << str << endl;
}

int main () {
const char * c = "sample text";
print ( const_cast (c) );
return 0;
}
sample text


typeid

typeid allows to check the type of an expression:


typeid (expression)


This operator returns a reference to a constant object of type type_info that is defined in the standard header file . This returned value can be compared with another one using operators == and != or can serve to obtain a null-terminated character sequence representing the data type or class name by using its name() member.

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// typeid
#include
#include
using namespace std;

int main () {
int * a,b;
a=0; b=0;
if (typeid(a) != typeid(b))
{
cout << "a and b are of different types:\n";
cout << "a is: " << typeid(a).name() << '\n';
cout << "b is: " << typeid(b).name() << '\n';
}
return 0;
}
a and b are of different types:
a is: int *
b is: int


When typeid is applied to classes typeid uses the RTTI to keep track of the type of dynamic objects. When typeid is applied to an expression whose type is a polymorphic class, the result is the type of the most derived complete object:

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// typeid, polymorphic class
#include
#include
#include
using namespace std;

class CBase { virtual void f(){} };
class CDerived : public CBase {};

int main () {
try {
CBase* a = new CBase;
CBase* b = new CDerived;
cout << "a is: " << typeid(a).name() << '\n';
cout << "b is: " << typeid(b).name() << '\n';
cout << "*a is: " << typeid(*a).name() << '\n';
cout << "*b is: " << typeid(*b).name() << '\n';
} catch (exception& e) { cout << "Exception: " << e.what() << endl; }
return 0;
}
a is: class CBase *
b is: class CBase *
*a is: class CBase
*b is: class CDerived