the same id in the same scope refers to different objects

[Jonathan Wakely]

On 4 September 2017 at 14:17, Andrew Makhorin wrote:
> On Mon, 2017-09-04 at 10:33 +0100, Jonathan Wakely wrote:
>> On 3 September 2017 at 11:43, Andrew Makhorin wrote:
>> > Why x used to initialize y identifies not the same object as x used in
>> > printf though x is the same identifier within the same block scope?
>>
>> Because that's how scope and visibility works in the C programming
>> language. A name is only in scope after it has been declared. Get a
>> good book on C programming.
>>
>
> Thank you for your reply.
>
> I think the ISO C Standard is a good book. The subsection 6.2.1
> "Scopes of identifiers" says:
>
>    Different entities designated by the same identifier either have
>    different scopes, or are in different name spaces.
>    [...]
>    Two identifiers have the same scope if and only if their scopes
>    terminate at the same point.
>
> In my example program x used in printf has block scope which overlaps
> the file scope where other x is declared. Thus, the behavior of my
> example program is undefined, because x is used to initialize y before
> it is assigned an initial value (this is similar to the case when a
> goto jumps into a block bypassing possible initialization of variables
> declared within that block).

No, that's wrong, there's no undefined behaviour. But it's off-topic
on the GCC mailing lists.