AMDG Martin Bonner <Martin.Bonner <at> pi-shurlok.com> writes:
From: Simonson, Lucanus J
There are cases where reading the C++ standard will inform a developer that reinterpret_cast is safe [snip]. Specifically, I submit that inheritance and composition are such cases
As I said in my previous email, I don't think so. BUT...
provided that additional data members are not added in the subtype or composed type.
... I missed this.
I still don't think the standard makes the guarantees you think it does, but in practise, you are much less likely to run into problems with that limitation.
If the types are inherited (rather than composed) I still think you have problems if the derived class overrides virtuals in the base.
Even without overriding virtuals, technically such a cast is wrong. "If a nonstatic member function of a class X is called for an object that is not of type X, or of a type derived from X, the behavior is undefined." (9.3.1/1) In other words, you can do the reinterpret_cast to and from the derived class, and that is guaranteed to work, but you cannot call a member function and cast the this pointer back to the base. While what you are doing will probably work I can imagine a case where the compiler helpfully inserts code for detecting such a cast (Since for non-aggregates the compiler is permitted to add extra hidden members) In Christ, Steven Watanabe