Re: Question about inheritance

[Ben Scherrey <scherrey at gte dot net>]

This is a C++ language issue and not related to the egcs compiler
implementation. Suffice to say, the scope of doit is strictly within
foo. You have two typedefs, specifically foo::hi and stuff::hi. Their
only similarities are the coincidence of their names which, as a
typedef, means nothing in a strongly typed language. To get the result
you request (but probably not what you want) try the following:

struct foo
{ 
	typedef int hi;
	virtual size_t hi_size( void ) const { return sizeof( hi ) };
	void doit( void ) const
	{	// What if you do sizeof( void* ), bool, et al ?
		// This will usually say "int" on most platforms!
		if( hi_size() == sizeof( int ) )
			puts("int");
		else
			puts("something else");
	}
};

struct stuff : public foo
{
	typedef float hi;
	virtual size_t hi_size( void ) const { return sizeof( hi ) };
};

	I think you're barking up the wrong tree here...

		Ben Scherrey

Peter V. Evans wrote:
> 
> Hi,
> 
> I'm developing a program which makes heavy usage of inheritance.  Let me
> give the example first:
> 
> class foo
> {
> public:
>         typedef int hi;
> 
>         void doit (void)
>         {
>                 if (sizeof(hi) == sizeof(int))
>                         puts("int");
>                 else
>                         puts("something else");
>         }
> };
> 
> class stuff : public foo
> {
> public:
>         typedef double hi;
> };
> 
> int
> main (void)
> {
>         stuff s;
> 
>         s.doit();       // Prints out "int", not "something else"
>         return 0;
> }
> 
> ---
> 
> The function doit, thus, does not see the derived class' "hi", only the
> parent class.  I couldn't say if this is the correct behaviour, since I
> don't know C++ as well as most others, but a better question would be,
> how to get doit to somehow see the derived class "hi" instead of the
> parent class "hi"?
> 
> Thanks for any help you can provide.
>         Peter