sizeof an array data member

[MR <nimrod dot bm at optusnet dot com dot au>]

HI All, 

I realise this might be a dumb question, but here goes.

if I have a method:
    const int operator[](const char *) const {
 	    int len;
	    int numer = sizeof (this->data);
	    int denom = sizeof data[0];
 	    len = numer  / denom;

 	    return len;
    }

and a private data member....
private:
    float * data;

that I use as an array of floats by alocating to it with new[], 
why does the [] overload always return 1?  I was hopeful that 
it might give me the size of the array!

Thanks, 

Matt