Should such type conversions be safe?

[Alan Curry]

Alan DeKok writes the following:
>
>"chen jin" <celadonbird@hotmail.com> wrote:
>> the coding coverts forcibly CONF_ITEM pointer to CONF_ITEM_SECTION pointer,
>> but the two structs are of different structure,How can they be safely 
>> converted?
>
>  In general, they can't.  C allows compilers to re-arrange the
>elements of a data structure, so the structures can't be cast.

pad, yes. rearrange, no.

It is allowed to cast a pointer to a struct to a pointer to its first
element, which is what I did with the CONF_ subclasses.