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From: ian@rathe.cs.umn.edu (Ian Hogg)
Newsgroups: comp.lang.c++
Subject: Re: Inheritance  & type conversion
Message-ID: <1991Jun6.140159.9208@rathe.cs.umn.edu>
Date: 6 Jun 91 14:01:59 GMT
References: <2348@taurus.cs.nps.navy.mil>
Organization: Rathe, Inc.
Lines: 56

In article <2348@taurus.cs.nps.navy.mil> skip@taygeta.oc.nps.navy.mil (Skip Carter) writes:
>
>	I have been programming C++ for the past few months, using Turbo C++
>        V1.0 and Zortech C++ V2.1.  In the process of writing an application
>        I came across the following behaviour, which I don't understand:
>
>
>        There are two classes, Base and Derived.
>        
>        Derived is derived from the Base class and has a method to do a
>        	type conversion from Derived TO Base.

		You don't need to define a conversion from Derived to Base.  An object
		of type derived can be used anywhere an object of base is expected.
>
>	Base has friends functions, report1 and report2.  Report1 takes a
>        	reference to a Base, report2 takes the value of a Base,
>                as the parameter.
>
>	The following:                
>                
>        	Derived dtype;
>
>        	report1( dtype );
>               
>      	causes a conversion to Base then report1 is invoked with Turbo C++,
>        but for Zortech C++ NO CONVERSION occurs.
>        
>        
>        BUT:
>                  
>        	Derived dtype;
>
>        	report2( dtype );
>               
>
>	cases a conversion to Base with Zortech C++, BUT NOT for Turbo C++     
>          
>
>
>
>	I am too much of a novice to be able to figure out which is the
>        correct behavior.  Can anyone give me some insight ?  I have attached
>        a copy of the simple program.
>        

   I don't know which is correct but I would expect no conversion to take place
   in either place.  The compiler should only apply conversions whenever 
   necessary, and they aren't in this case.


-- 
Ian Hogg                        email:  rathe!ian@cs.umn.edu
                                        ...!umn-cs!rathe!ian
Rathe, Inc                              ianhogg@cs.umn.edu
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