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From: cimshop!davidm@uunet.UU.NET (David S. Masterson)
Newsgroups: comp.lang.c++
Subject: Re: Reference problem??
Message-ID: <CIMSHOP!DAVIDM.91Apr25095910@uunet.UU.NET>
Date: 25 Apr 91 16:59:10 GMT
References: <CIMSHOP!DAVIDM.91Apr24233547@uunet.UU.NET>
Sender: davidm@cimshop.UUCP
Distribution: comp
Organization: Consilium Inc., Mountain View, California
Lines: 71
In-reply-to: cimshop!davidm@uunet.UU.NET's message of 25 Apr 91 06:35:47 GMT

>>>>> On 25 Apr 91 06:35:47 GMT, [I] said:

Me> #ifdef GPLUSPLUS
Me> #include <stream.h>
Me> #else
Me> #include <iostream.h>
Me> #include <iomanip.h>
Me> #endif

Me> class alpha {			// top of the hierarchy
Me> 	int	value1;
Me> public:
Me> 	alpha(int a) : value1(a) {}
Me> 	virtual void display() {
Me> 		cout << "Alpha value1 " << value1 << "\n";
Me> 	}
Me> };

Me> class beta : public alpha {	// middle of the hierarchy
Me> 	int	value2;
Me> public:
Me> 	beta(int a, int b) : alpha(a), value2(b) {}
Me> 	virtual void display() {
Me> 		alpha::display();
Me> 		cout << "Beta value2 " << value2 << "\n";
Me> 	}
Me> };

Me> class gamma : public beta {		// bottom of the hierarchy
Me> 	int	value3;
Me> public:
Me> 	gamma(int a, int b, int c) : beta(a, b), value3(c) {}
Me> 	virtual void display() {
Me> 		beta::display();
Me> 		cout << "Gamma value3 " << value3 << "\n";
Me> 	}
Me> };

Me> void testfunc(alpha*& parm) {
Me> 	cout << "testfunc display\n";
Me> 	parm = new alpha(40);
Me> 	parm->display();
Me> }

Me> int main() {
Me> 	gamma	g(10, 20, 30);
Me> 	cout << "first display\n";
Me> 	g.display();
Me> 	cout << "second display\n";
Me> 	gamma	*gptr = &g;
Me> 	gptr->display();
Me> 	testfunc((alpha*) gptr);
		// ^-- why is the cast necessary?
Me> 	cout << "third display\n";
Me> 	gptr->display();
Me> }
Me> // End of the program

I don't understand why the cast is necessary.  Without the cast, Oregon C++,
Turbo C++, and G++ tells me something like:

    Warning: Lvalue coerced into temporary to initialize reference type

Can anyone explain why?
--
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