https://gcc.gnu.org/gcc-7/changes.html

[Jonathan Wakely]

On 11 July 2017 at 17:51, Jonny Grant wrote:
> Hello
> https://gcc.gnu.org/gcc-7/changes.html
>
> snprintf (d, sizeof d, "%#02x", x & 0xff);
>
>                ^^
> Should be:   sizeof(d)  ?

"The sizeof operator yields the size (in bytes) of its operand, which
may be an expression or the parenthesized name of a type."

So the parentheses are only required for a type, not an expression.
sizeof(d) is the same as sizeof d which is the same as
sizeof(((((d))))).