Re: function pointers in C++

[Elias Athanasopoulos <elathan@phys.uoa.gr>]

On Mon, Mar 15, 2004 at 11:21:18AM -0300, Sandro Dangui wrote:
> 
> I think this sample code will help you... Verify if it looks brilliant
> enough. :-))

Thanks for the detailed reply. 

Actually, what I want to do is to pass a pointer to a member function in
a function that expects a pointer to function; I don't want to call the
member function, but just pass its address.

Following Stroustrup (pages 156..158), I did something like this:

    Foo *f = new Foo(id);
    double (Foo::*pfunc)(double *, double *) = &Foo::func;
    Bar *res = new Bar((double (*)(double *, double *))(func->*pfunc));

And:

class Foo {
public:
    Foo(int id);
    ~Foo();
    double func(double *, double *);
};

Also Bar's constructor (I can't change it --third party implementation) is:

    Bar(double (*)(double *, double *));

Amazingly I get the error:

test.cxx:107: error: converting from `double (Foo::*)(double*, double*)' to 
   `double (*)(double*, double*)'
   
which is *at least* annoying. It is another BIG suprise from C++. I mean,
there is, most probably, a good reason why this is not supported, but it is
a *broken design*.

Foo::func()'s prototype is (double) (double *, double *), which in my human
brain is compiled as: 'give me two pointers to double and I will give you one
double'. Why I can't pass it to a function which *expects* what my poor human brain
understands?

I didn't ask to convert for me a string to float...

Regards,
-- 
University of Athens			I bet the human brain 
Physics Department				is a kludge --Marvin Minsky