C++ typeid()

Does anyone know how typeid() is implemented in C++???
I mean, how do I make a function like typeid() where I can pass the TYPE as a paramter.

Example:
int main()
{
    typeid(int);//<-- works of course
    f(int);//<-- how to do something like this
           //        without using macros or templates
}

how to pass a type
#include <typeinfo.h>
idiot_function(type_info t);

idiot_function(typeid(*pA));

now idiot_function can find out whatever the fuck it wants about pA's type. isn't this what you're trying to do?