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.
