Re: [Qemu-devel] [PATCH 1/2] block/qapi: make two printf() formats literal

[Peter Xu <peterx@redhat.com>]

On Mon, Mar 21, 2016 at 03:14:48PM -0600, Eric Blake wrote:
> On 03/09/2016 06:46 PM, Peter Xu wrote:
> > 
> > Is this a grammar btw?
> 
> Yes, C has an ugly grammar, because [] is just syntactic sugar for
> deferencing pointer addition with nicer operator precedence.  Quoting
> C99 6.5.2.1:
> 
> "The definition of the subscript operator [] is that E1[E2] is identical
> to (*((E1)+(E2))).  Because of the conversion rules that apply to the
> binary + operator, if E1 is an array object (equivalently, a pointer to
> the initial element of an array object) and E2 is an integer, E1[E2]
> designates the E2-th element of E1 (counting from zero)."
> 
> And a string literal is just a fancy way of writing the address of an
> array of characters (where the address is chosen by the compiler).
> 
> Thus, it IS valid to dereference the addition of an integer offset with
> the address implied by a string literal in order to obtain a character
> within the string.  And since the [] operator is commutative (even
> though no one in their right mind commutes the operands), you can also
> write the even-uglier:
> 
> composite["\n "]
> 
> But now we've gone far astray from the original patch review :)

Interesting thing to know.  Thanks. :)

-- peterx