On Wed, 13 Nov 2013, Richard Biener wrote: > On Wed, Nov 13, 2013 at 1:39 AM, Joseph S. Myers > <jos...@codesourcery.com> wrote: > > <stdatomic.h> contains what C11 describes as "generic functions". > > Although DR#419 makes clear that users cannot #undef these macros (or > > otherwise suppress use of a macro definition) and expect to find an > > underlying function, they still need to behave like functions as > > regards evaluating their arguments exactly once (see C11 7.1.4). > > > > I noted when adding <stdatomic.h> to mainline that some of the macro > > definitions there failed that requirement in the case where the > > pointer argument had variably modified type, because then typeof > > evaluates its argument and so that argument would be evaluated twice. > > Avoiding such double evaluation requires defining the type of a > > temporary variable, and initializing it with the pointer argument, > > with a single evaluation. To achieve this, this patch adds a new GNU > > C extension __auto_type, essentially a restricted version of C++11 > > auto, and uses it in <stdatomic.h>. > > I suppose you didn't use '__auto' because that's much more likely > used elsewhere than '__auto_type'?
My reasoning was that it's normal in other cases for "__keyword" to mean the same as plain "keyword", so it would be confusing for "__auto" to mean something different from standard C "auto". -- Joseph S. Myers jos...@codesourcery.com
