[lug] typeid calls in g++ 2.95.2

[D. Stimits]

"Scott A. Herod" wrote:
> 
> Sorry to post a C++ question but it is rather specific to the egcs
> compilers.
> 
> Does anyone know if typeid works correctly on the egcs compilers, or
> perhaps I am not using it correctly.  In the code posted just below,
> I would expect the output to be:
> 
> ------------------------------
> This is a B
> We got a P1B while a b* is P1B
> ------------------------------
> 
> but I get
> 
> ------------------------------
> This is a B
> We got a P1A while a b* is P1B
> ------------------------------
> 
> The code is just below.  Compile with "g++ filename.C".
> Thanks,
> Scott
> 
> --------------------------------
> #include <typeinfo>
> #include <stream.h>
> 
> class A {
> public:
>     A() {};
>     virtual ~A() {};
>     virtual void spam() { cout << "This is an A" << endl; }
> };
> 
> class B : public A {
> public:
>     B() {};
>     virtual ~B() {};
>     virtual void spam() { cout << "This is a B" << endl; }
> };
> 
> int whatis( A* a ) {
              ^^
Here you have specifically told it you are looking for an "A". The
argument "a" has been defined as type "A", and although it can hold a
"B" (which IS an "A"), it will always be "A". Polymorphism is working
correctly here, that it uses the method of "B", but considers it type
"A".

>     a->spam();
>     cout << "We got a " << typeid( a ).name()
>          << " while a b* is " << typeid( B* ).name()
>          << endl;
> }
> 
> int main ( int argc, char *argv[] ) {
>     B* b = new B;
>     whatis( b );
>     return 0;
> }
> -------------------------------------------
> 
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