Re: [TUHS] C++ / Kernel

[Nevin Liber <nevin@eviloverlord.com>]

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On Thu, Aug 23, 2018 at 5:17 PM <ron@ronnatalie.com> wrote:

> This union was right in the middle of the buf struct:
>
>         union {
>             caddr_t b_addr;             /* low order core address */
>             int *b_words;               /* words for clearing */
>             struct filsys *b_filsys;    /* superblocks */
>             struct dinode *b_dino;      /* ilist */
>             daddr_t *b_daddr;           /* indirect block */
>         } b_un;
> There were a number of other places that did the same thing.   It's
> OFFICIALLY now in undefined behavior by the standard (though of course that
> didn't exist in the BSD days) ,
> to store in one element of the union and retrieve it via another.


It was still kinda frowned upon in K&R1:  "It is the responsibility of the
programmer to keep track of what type is currently stored in a union; the
results are machine dependent if something is stored as one type and
extracted as another."
-- 
 Nevin ":-)" Liber  <mailto:nevin@eviloverlord.com>  +1-847-691-1404

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