Somewhere lies a bug. The following code snippet:
#include <stdio.h>
#include <time.h>
int main()
{
struct tm t;
time_t now = time((void*)0);
localtime_r(&now, &t);
t.tm_isdst = 1;
printf("%ld\n", mktime(&t));
t.tm_isdst = 0;
printf("%ld\n", mktime(&t));
t.tm_isdst = -1;
printf("%ld\n", mktime(&t));
}
Yields:
1618928503
1618932103
1618932103
This is true on FreeBSD 13 and Ubuntu 18.04, both fully patched.
-michael
On Tue, Apr 20, 2021 at 7:04 AM Richard Cochran <[email protected]>
wrote:
> On Tue, Apr 20, 2021 at 11:44:06AM +0200, Lars Munch wrote:
> > tm_isdst needs to be initialized to make sure mktime does not fail
> > or calculates the wrong time.
>
> No, take a look at the mktime(3) man page. There you will read the
> following.
>
> The mktime() function modifies the fields of the tm structure as
> fol‐
> lows: tm_wday and tm_yday are set to values determined from the
> con‐
> tents of the other fields; if structure members are outside
> their
> valid interval, they will be normalized (so that, for example, 40
> Oc‐
> tober is changed into 9 November); tm_isdst is set (regardless of
> its
> initial value) to a positive value or to 0, respectively, to
> indicate
> whether DST is or is not in effect at the specified time.
>
> Thanks,
> Richard
>
>
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