subtracting days from localtime problem

[ALeine]

ganbold at micom.mng.net wrote: 

> One more question, what will happen next time when
> time goes back in October?
> Does following line correct it as same as now?
> 
> /* make mktime(3) figure out whether DST is in effect */
> t->tm_isdst = -1;

Yes, it will work correctly. You can see what happens by
setting now to 1131131131 (where you currently have
now = time(NULL)). It's not an April Fools' Day joke, that
just happens to be an appropriate time in November. :-)

I also noticed a number of bugs in your code that you may
want to fix:

- memory leak: you are allocating memory with my_alloc(),
  but then you neither free(3) it nor keep track of it.
  You should remove my_alloc() and just create a buffer
  in main() and then pass it by reference to functions that
  need to modify its contents.

- with my_alloc() you basically reinvented strdup(3), see
  man 3 strdup for details. You do not need strdup(3) for
  what you want to achieve, just pass the buffer from main()
  by reference and then use snprintf(3) to modify its contents.

- snprintf(3) handles the size argument correctly, meaning
  that you should specify the full size of the string since
  at most size-1 characters are written with guaranteed NULL
  termination, see man 3 snprintf for details.

ALeine
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