Can a pass-by-reference var be assigned to a local var?

[Matthew Hagerty]

Justin,

Yes, after reading your post, I found this:

--
Structure Assignments

ANSI C compilers allow the information in one structure to be assigned to
another structure, as in:

     binfo=addr_info;
--

I never knew that.  I wonder why that functionality is done for structs,
but not extended to arrays as well?  Why make exceptions for structs like
that?

Thanks for clearing that up for me!

Matthew


> I think you're missing something.
>
> This is "structure assignment" in action.  The variable 'sbp' is a
> *statb, and the assignment assigns a structure, sb2, to *sbp, which is
> itself a structure, not a pointer.
>
> Regards,
>
> Justin
>
> On Wednesday, July 2, 2003, at 10:54 AM, Matthew Hagerty wrote:
>
>> Greetings,
>>
>> I was looking over the code for the tail command and found something
>> that
>> seems wrong.  Below is the abbreviated code that highlights my concern.
>> Basically, sb is defined in main() and passed to forward() (and
>> reverse())
>> by reference.  Then in forward() sb2 is defined, and finally sb is set
>> to
>> sb2.
>>
>> Two things come to mind that don't seem right: 1. What happens to sb
>> when
>> forward() returns?  It was pointing to sb2 which was a local var of
>> forward()...  and 2. The assignment *sbp = sb2 happens in a loop and
>> could
>> be executed more than once, which seems to make the comparisons just
>> prior
>> to the assignment usless 2 or more loop iterations.
>>
>> Am I missing something?  It seems to me that instead of *sbp = sb2, it
>> should be done with memcpy() or something?  Any insight would be
>> greatly
>> appreciated.
>>
>> Thanks,
>> Matthew
>>
>>
>> In tail.c:
>>
>> int
>> main(argc, argv)
>>   int argc;
>>   char *argv[];
>> {
>>   struct stat sb;
>> .
>> .
>>   if ((fp = fopen(fname, "r")) == NULL ||
>>     fstat(fileno(fp), &sb)) {
>> .
>> .
>>   if (rflag)
>>     reverse(fp, style, off, &sb);
>>   else
>>     forward(fp, style, off, &sb);
>> .
>> .
>> }
>>
>> Then in forward.c:
>>
>> void
>> forward(fp, style, off, sbp)
>>   FILE *fp;
>>   enum STYLE style;
>>   off_t off;
>>   struct stat *sbp;
>> {
>>   int ch, n, kq = -1;
>>   int action = USE_SLEEP;
>>   struct kevent ev[2];
>>   struct stat sb2;
>>   struct timespec ts;
>> .
>> .
>>     if (Fflag && fileno(fp) != STDIN_FILENO) {
>>       while (stat(fname, &sb2) != 0)
>>       /* file was rotated, wait until it reappears */
>>         (void)sleep(1);
>>       if (sb2.st_ino != sbp->st_ino ||
>>         sb2.st_dev != sbp->st_dev ||
>>         sb2.st_rdev != sbp->st_rdev ||
>>         sb2.st_nlink == 0) {
>>         fp = freopen(fname, "r", fp);
>>         if (fp == NULL) {
>>           ierr();
>>           return;
>>         } else {
>>           *sbp = sb2;
>>           action = ADD_EVENTS;
>>         }
>>       }
>>     }
>> .
>> .
>> }
>>
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> --
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