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Localtime: fix daylight time documentation and computation.

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This commit is contained in:
antirez 2018-07-04 14:09:07 +02:00
parent 243c5a7a30
commit 6614d30599
1 changed files with 14 additions and 4 deletions
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18
src/localtime.c
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@ -39,7 +39,12 @@
* This function takes the timezone 'tz' as argument, and the 'dst' flag is * This function takes the timezone 'tz' as argument, and the 'dst' flag is
* used to check if daylight saving time is currently in effect. The caller * used to check if daylight saving time is currently in effect. The caller
* of this function should obtain such information calling tzset() ASAP in the * of this function should obtain such information calling tzset() ASAP in the
* main() function, and later accessing the globals 'timezone' and 'daylight'. * main() function to obtain the timezone offset from the 'timezone' global
* variable. To obtain the daylight information, if it is currently active or not,
* one trick is to call localtime() in main() ASAP as well, and get the
* information from the tm_isdst field of the tm structure. However the daylight
* time may switch in the future for long running processes, so this information
* should be refreshed at safe times.
* *
* Note that this function does not work for dates < 1/1/1970, it is solely * Note that this function does not work for dates < 1/1/1970, it is solely
* designed to work with what time(NULL) may return, and to support Redis * designed to work with what time(NULL) may return, and to support Redis
@ -57,6 +62,7 @@ void nolocks_localtime(struct tm *tmp, time_t t, time_t tz, int dst) {
const time_t secs_day = 3600*24; const time_t secs_day = 3600*24;
t -= tz; /* Adjust for timezone. */ t -= tz; /* Adjust for timezone. */
t += 3600+dst; /* Adjust for daylight time. */
time_t days = t / secs_day; /* Days passed since epoch. */ time_t days = t / secs_day; /* Days passed since epoch. */
time_t seconds = t % secs_day; /* Remaining seconds. */ time_t seconds = t % secs_day; /* Remaining seconds. */
@ -101,13 +107,17 @@ void nolocks_localtime(struct tm *tmp, time_t t, time_t tz, int dst) {
#include <stdio.h> #include <stdio.h>
int main(void) { int main(void) {
tzset(); /* Obtain timezone and daylight info. */
tzset(); /* Now 'timezome' global is populated. */
time_t t = time(NULL); time_t t = time(NULL);
struct tm *aux = localtime(&t);
int daylight_active = aux->tm_isdst;
struct tm tm; struct tm tm;
char buf[1024]; char buf[1024];
nolocks_localtime(&tm,t,timezone,daylight); nolocks_localtime(&tm,t,timezone,daylight_active);
strftime(buf,sizeof(buf),"%d %b %H:%M:%S",&tm); strftime(buf,sizeof(buf),"%d %b %H:%M:%S",&tm);
printf("[timezone: %d, dl: %d] %s\n", (int)timezone, (int)daylight, buf); printf("[timezone: %d, dl: %d] %s\n", (int)timezone, (int)daylight_active, buf);
} }
#endif #endif