On Mon, Apr 1, 2019 at 8:36 PM Kurt H Maier <k...@sciops.net> wrote: > On Mon, Apr 01, 2019 at 08:26:30PM -0400, Jeremy O'Brien wrote: > > On Mon, Apr 1, 2019, at 11:33, Kyohei Kadota wrote: > > > Hi, 9fans. I use 9legacy. > > > > > > About below program, I expected that flags field will initialize to > > > zero but the value of flags was a garbage, ex, "f8f7". > > > Is this expected? > > > > > > ``` > > > #include <stdio.h> > > > > > > struct option { > > > int n; > > > char *s; > > > int flags; > > > }; > > > > > > int > > > main(void) > > > { > > > struct option opt = {1, "test"}; > > > printf("%d %s %x\n", opt.n, opt.s, opt.flags); > > > return 0; > > > } > > > ``` > > > > > > > > > > According to C99: "If an object that has automatic storage duration is > not initialized explicitly, its value is indeterminate." > > > > Stack variable == automatic storage duration. This appears to be correct > behavior to me. > > > > Can anyone provide the patches 9legacy uses to implement C99 compliance?
There were actually quite a few of them, mostly done by Geoff Collyer. The compiler sources list contains a list of desiderata in a file called `c99`; of course, the plan9 compilers aren't completely compliant (they weren't trying to be). Incidentally this file has been carried forward into, for example, /sys/src/cmd/cc/c99 in the 9front distribution (and other plan9 derivatives). In the present case, this appears to be a compiler bug. The aforementioned reference to n1548 sec 6.7.9 para 10 is incorrect in that there _is_ an explicit initializer here. The relevant text in the standard is sec 6.7.9 pp 16-21, which specifies that in the event that an explicit initializer does not completely cover (in a topological sense) the thing it is initializing, then the elements not covered shall be initialized as if they had _static_ storage duration; that is, they should be zeroed. Now as I said, the Plan 9 C compilers aren't explicit C99 compliant. But given that the `c99` file describes things related to initializer lists as being unneeded because they were already implemented, one may assume it was believed that this was covered by c99 behavior. It isn't. - Dan C.