为什么 mktime() 将 31/03/2019 02:00 转换为 01:00 且 tm.tm_isdst = 1 且具有 CET 时区?
我认为这是一个无效的组合。
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
void reset(struct tm* tm){
(*tm) = (const struct tm){0};
tm->tm_sec = 0;
tm->tm_min = 1;
tm->tm_hour = 2;
tm->tm_mon = 2;
tm->tm_mday = 31;
tm->tm_year = 2019 - 1900;
}
int main(int argc, char **argv)
{
struct tm tm;
int secs;
reset(&tm);
printf("Before mktime\n");
printf(" %04d-%02d-%02d %02d:%02d:%02d\n", tm.tm_year+1900, tm.tm_mon+1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec);
tm.tm_isdst = 0;
secs = mktime(&tm);
printf("After mktime tm.tm_isdst = 0;\n");
printf(" %04d-%02d-%02d %02d:%02d:%02d TZ=%s , tm_isdst = %d, timestamp=%i\n", tm.tm_year+1900, tm.tm_mon+1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec, tm.tm_zone, tm.tm_isdst, secs);
reset(&tm);
tm.tm_isdst = 1;
secs = mktime(&tm);
printf("After mktime tm.tm_isdst = 1;\n");
printf(" %04d-%02d-%02d %02d:%02d:%02d TZ=%s , tm_isdst = %d, timestamp=%i\n", tm.tm_year+1900, tm.tm_mon+1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec, tm.tm_zone, tm.tm_isdst, secs);
reset(&tm);
tm.tm_isdst = -1;
secs = mktime(&tm);
printf("After mktime tm.tm_isdst = -1\n");
printf(" %04d-%02d-%02d %02d:%02d:%02d TZ=%s , tm_isdst = %d, timestamp=%i\n", tm.tm_year+1900, tm.tm_mon+1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec, tm.tm_zone, tm.tm_isdst, secs);
return 0;
}
输出:
% date
Sun Mar 31 06:50:42 CEST 2019
% test_mktime
Before mktime
2019-03-31 02:01:00
After mktime tm.tm_isdst = 0;
2019-03-31 03:01:00 TZ=CEST , tm_isdst = 1, timestamp=1553994060
After mktime tm.tm_isdst = 1;
2019-03-31 01:01:00 TZ=CET , tm_isdst = 0, timestamp=1553990460
After mktime tm.tm_isdst = -1
2019-03-31 03:01:00 TZ=CEST , tm_isdst = 1, timestamp=1553994060
最佳答案
- 2019-03-31 02:01:00 CET(
is_dst = 0
,UTC+1)不存在,但等同于 2019-03-31 01:01:00 UTC (纪元后 1553994060 秒),相当于 2019-03-31 03:01:00 CEST(is_dst = 1
,UTC+2)。 - 2019-03-31 02:01:00 CEST(
is_dst = 1
,UTC+2)不存在,但等同于 2019-03-31 00:01:00 UTC (纪元后 1553990460 秒),相当于 2019-03-31 01:01:00 CET (is_dst = 0
, UTC+1)。 (注:1553994060 - 1553990460 = 3600,相差1小时。) - 对于
is_dst = -1
,该实现会尝试确定夏令时是否有效,但由于 2019-03-31 02:01:00 对于 CET 和 CEST 同样无效,它只是选择一个或另一个。在这种情况下,它假设输入是在标准时间 2019-03-31 02:01:00 CET (is_dst = 0
, UTC+1),这不存在,但等同于2019-03-31 01:01:00 UTC(纪元后 1553994060 秒),相当于 2019-03-31 03:01:00 CEST (is_dst = 1
, UTC+2) .
关于c - 奇怪的 mktime() 行为,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/55903387/