> Date: Sat, 07 Aug 2021 22:59:02 +0700
> From: Robert Elz <k...@munnari.oz.au>
>
> Date: Wed, 4 Aug 2021 17:52:46 -0700
> From: Jason Thorpe <thor...@me.com>
> Message-ID: <68ff8737-f347-4a7f-960b-9e4a6ca9e...@me.com>
>
> | It addresses the concerns about compile-time type checking
> | by using an anonymous structure constructed in-line
>
> Is there something in the C definition of such things which guarantees
> that the un-init'd fields all get set to 0/NULL ? Or is that just
> happening because of the "const" spread all over - which might be causing
> the compiler to allocate static storage, but which is not required of const?
>
> Also, is there some way to distinguish an integer valued attribute which
> is explicitly set to 0 from one which isn't set at all (in which case we
> might want to default it to some other value) or do we only ever use
> attributes via various kinds of pointers (or perhaps never have any,
> anywhere ever, where 0 is a sensible value) ?
C11, Sec. 6.7.9 `Initialization', paragraph 19, p. 141:
`The initialization shall occur in initializer list order, each
initializer provided for a particular subobject overriding any
previously listed initializer for the same subobject; all
subobjects that are not initialized explicitly shall be initialized
implicitly the same as objects that have static storage duration.'
And paragraph 10, p. 140:
`....If an object that has static or thread storage duration is not
initialized explicitly, then:
`--- if it has pointer type, it is initialized to a null pointer;
`--- if it has arithmetic tpye, it is initialized to (positive or
unsigned) zero;
`--- if it is an aggregate, every member is initialized
(recursively) according to these rules, and any padding is
initialized to zero bits;
`--- if it is a union, the first named member is initialized
(recursively) according to these rules, and any padding is
initialized to zero bits.'
So pointers are nulled and integers are zero'd here -- and const is
not relevant, nor does the storage for these objects actually have
static duration; it's just that the anonymous struct objects with
designated initializers are initialized the same way as if they did
have static storage duration.
