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. Thus it became obvious that support for run-time type information was needed at the language level.

There are three main C++ language elements to run-time type information:

1)The dynamic_cast operator. :- Used for conversion of polymorphic types.

class B { ... };
class C : public B { ... };
class D : public C { ... };

void f(D* pd)
{
C* pc dynamic_cast<C*>(pd);// ok: C is a direct base class
// pc points to C subobject of pd

B* pb dynamic_cast<B*>(pd);// ok: B is an indirect base class
// pb points to B subobject of pd
...
}
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2)The typeid operator :- Used for identifying the exact type of an object.

3)The type_info class :- Used to hold the type information returned by the typeid operator.The type_info class describes type information generated within the program by the compiler.

NOTE:- TRY THIS EXAMPLE IS COMPILE AND LINK USING MSVC++ 6.0 CL.EXE Compiler and Linker PLS CHECK SAME typid available in UNIX based C++;
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#include stdio.h
#include <typeinfo.h>

class A
{
public:
};

class B:public A
{
public:
};

int main(int argc char* argv[])
{
int iVal int();
float fVal float();
char cVal char();
A a a1;
B b;

const type_info& t_iVal typeid(iVal); // Holds Simple int DataType Info
const type_info& t_iValRef typeid(&iVal); // Holds pointer type_info
printf( \n Type Info of iVal s\n t_iVal.name());
printf( \n Type Info of &iVal s\n t_iValRef.name());

printf( \n Type Info of fVal s\n typeid(fVal).name());
printf( \n Type Info of &fVal s\n typeid(&fVal).name());

printf( \n Type Info of cVal s\n typeid(cVal).name());
printf( \n Type Info of &cVal s\n\n typeid(&cVal).name());

printf( \n Type Info of a s\n typeid(a).name());
printf( \n Type Info of b s\n\n typeid(b).name());

if(typeid(a) typeid(a1))
{
printf( \n BOTH INSTANCES a AND a1 BELONGS TO SAME CLASS \n\n );
}

return 0;
}
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