[Mono-dev] Segfault on base class method access

Robert Jordan robertj at gmx.net
Wed Nov 28 10:53:58 EST 2007

Paul Melis wrote:
> Hello,
> I tried to register at the bug tracker, but did not receive a 
> confirmation mail, so I post here instead.
> When running the code below mono segfaults. The stack trace is 
> not enlightening.

This is a stack overflow. When mono was compiled w/out "alt stack"
support, stack overflows are reported this way.

> The use case here is to prefix a class's string representation with its 
> base class's string representation.
> I know about "base", but I figured it only gives you the direct parent 
> and not the parent-of-parent.
> Btw, if class A is removed (also as base class to B) then this code 
> still segfaults. It seems to be the "this as ..." that's the problem.


> class C : B
> {
>     public override string ToString()
>     {
>         return String.Format("({0}) C", (this as A).ToString());
>     }
> };

You cannot do this, since even if you cast to a base class, the
overridden method will be taken. That's why a "base" call is necessary.


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