> [...], using the C standard guaranteed property that the address of
> the first member is the address of the structure, allowing to cast
> pointers in order to operate whether on the base structure or on the
> derived structure?
Which standard promises this, and what exactly does it promise? I've
been looking through C99 and the closest I've found so far is 6.5.2.3
#5, which is not quite the same:
6.5.2.3 Structure and union members
...
[#5] One special guarantee is made in order to simplify the
use of unions: if a union contains several structures that
share a common initial sequence (see below), and if the
union object currently contains one of these structures, it
is permitted to inspect the common initial part of any of
them anywhere that a declaration of the completed type of
the union is visible. Two structures share a common initial
sequence if corresponding members have compatible types
(and, for bit-fields, the same widths) for a sequence of one
or more initial members.
Also, "address" as a technical term in C99 is very fuzzy, to the point
where I doubt that the statement that "the address of the first member
is the address of the structure" has a defined meaning. (It certainly
will for many implementations, but that is not the same thing.) Have
more recent standards turned it into something more specific?
I really need to chase down a copy of something more recent and turn it
into a useful form...I've got pointers, but need to follow them.
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