VC, Virtual Function with Different Return Type

Virtual Function with Different Return Type

Author	Message
Bryan Driscol #1 / 5	Virtual Function with Different Return Type Can I give a virtual function in a derived class a different return type that the one in the base class? ie: class base{ virtual base* ptr() { return this; } Quote: } class derived:: public base{ virtual derived* ptr() { return this; } Quote: } Stroustrup seems to say that this is just fine ( The C++ Programming Language, 3rd Edition Section 15.6.2 pg 424). However, VC++ 6.0 says "error C2555: 'Cond::new_expr' : overriding virtual function differs from 'Expr::new_expr' only by return type or calling convention."
Sat, 28 Dec 2002 03:00:00 GMT

Neil Butterwort #2 / 5	Virtual Function with Different Return Type Quote: > Can I give a virtual function in a derived class a different return type > that the one in the base class? > ie: > class base{ > virtual base* ptr() { return this; } > } > class derived:: public base{ > virtual derived* ptr() { return this; } > } > Stroustrup seems to say that this is just fine ( The C++ Programming > Language, 3rd Edition Section 15.6.2 pg 424). However, VC++ 6.0 says > "error C2555: 'Cond::new_expr' : overriding virtual function differs from > 'Expr::new_expr' only by return type or calling convention." The C++ standard says "yes", but unfortunately VC++ has not caught up with the standard yet (and neither have many other compilers). NeilB
Sat, 28 Dec 2002 03:00:00 GMT

colin #3 / 5	Virtual Function with Different Return Type Quote: > Can I give a virtual function in a derived class a different return type > that the one in the base class? > ie: > class base{ > virtual base* ptr() { return this; } > } > class derived:: public base{ > virtual derived* ptr() { return this; } > } > Stroustrup seems to say that this is just fine ( The C++ Programming > Language, 3rd Edition Section 15.6.2 pg 424). However, VC++ 6.0 says > "error C2555: 'Cond::new_expr' : overriding virtual function differs from > 'Expr::new_expr' only by return type or calling convention." I think you're on to something here. I get the same errors in VC++ 6.3 after duplicating the Stoustup's example on pp.424-5. It sure seems this ought to work per Stroustrup's discussion. hmmm.... Compile errors are: D:\Code\vRetFunc\vRetFunc.cpp(21) : error C2555: 'Cond::new_expr' : overriding virtual function differs from 'Expr::new_expr' only by return type or calling convention D:\Code\vRetFunc\vRetFunc.cpp(7) : see declaration of 'Expr' D:\Code\vRetFunc\vRetFunc.cpp(22) : error C2555: 'Cond::clone' : overriding virtual function differs from 'Expr::clone' only by return type or calling convention D:\Code\vRetFunc\vRetFunc.cpp(7) : see declaration of 'Expr' Colin
Sat, 28 Dec 2002 03:00:00 GMT

Marco Dalla Gasperin #4 / 5	Virtual Function with Different Return Type Quote: > Can I give a virtual function in a derived class a different return type > that the one in the base class? In general no, unless you do this (what you did)... Quote: > class base{ > virtual base* ptr() { return this; } > } > class derived:: public base{ > virtual derived* ptr() { return this; } > } This is a standard feature that VC6 doesn't support. It has been part of C++ for a while now and people have been crying for MSVC++ to support it for the same ammount of time. Personally, I don't think it's that big of a deal. But, that's me. marco
Sat, 28 Dec 2002 03:00:00 GMT

Chris Uzdavini #5 / 5	Virtual Function with Different Return Type Quote: > Can I give a virtual function in a derived class a different return type > that the one in the base class? In C++, yes. In VC++, no. -- Chris
Sat, 28 Dec 2002 03:00:00 GMT

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