On 09/01/2019 19:15, Linus Torvalds wrote:
> On Wed, Jan 9, 2019 at 11:01 AM Ramsay Jones
> <ramsay@xxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> Ahem, so yes, both gcc and clang allow this (I just tested it), but
>> my reading of the C99 standard lead me to believe that this is not
>> valid C. (Not that it really matters).
>
> Interesting. Looking at the kernel, we actually have a lot of them, ie
>
> [torvalds@i7 linux]$ git grep 'struct.*= {[:space:]*}' | wc
> 1105 6766 81616
>
> although admittedly we also have a fair amount of the { 0 } kind:
>
> [torvalds@i7 linux]$ git grep 'struct.*= {[:space:]*0[:space:]*}' | wc
> 616 3722 50034
>
> and I didn't realize that the empty one might not even be standard.
>
OK, so I spent some time reading the C99 and C11 standards and
I _still_ can't see how this could be valid C!
So, I beat on gcc some more:
$ cat -n junk.c
1 #include <stdio.h>
2
3 int main (int argc, char *argv[])
4 {
5 struct { char *f; int i; } fred = {};
6 printf("fred.f %p (%s), fred.i %d\n", fred.f, fred.f, fred.i);
7 return 0;
8 }
$ gcc -std=c99 -pedantic -Wall -Wextra -o junk junk.cjunk.c: In function ‘main’:
junk.c:5:36: warning: ISO C forbids empty initializer braces [-Wpedantic]
struct { char *f; int i; } fred = {};
^
junk.c:3:15: warning: unused parameter ‘argc’ [-Wunused-parameter]
int main (int argc, char *argv[])
^~~~
junk.c:3:27: warning: unused parameter ‘argv’ [-Wunused-parameter]
int main (int argc, char *argv[])
^~~~
$ ./junk
fred.f (nil) ((null)), fred.i 0
$
... and finally got it to admit that {} is not ISO C (with -pedantic).
[I was starting to doubt myself! ;-) ]
ATB,
Ramsay Jones
