Problem with mktime() and difftime()

[Thanh Quang]

Hi, I had a problem with mktime() and difftime(). I need to calculate time interval between now and a specific time. I used LOGI to log my local_time and alarm_time, when I calculate time interval between someday in the same month, it works fine. But when I use difftime() to calculate time interval between 23:59:00 04/30/2022 and 07:00:00 05/01/2022, it likely add 86400 ( = 24*60*60 secs) to result. I tested for other month and it did too.
Please help me solve this problem.
Sorry for my English

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1. time_t i2clocaltime = mktime(&local_time);
2.   time_t alrmtime = mktime(&alarm_time);
3.   double remain_time = difftime(alrmtime,i2clocaltime);
4.   ESP_LOGI(TAG,"Alarm time %04d-%02d-%02d %02d:%02d:%02d",alarm_time.tm_year,alarm_time.tm_mon,alarm_time.tm_mday,alarm_time.tm_hour,alarm_time.tm_min,alarm_time.tm_sec);
5.   ESP_LOGI("Remain time","time %f",remain_time);

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Code: [Select all] [Expand/Collapse]

1. I (10623) MQTT_DAQ: today 2022-04-30 23:59:13
2. I (10623) MQTT_DAQ: Alarm time 2022-05-01 07:00:00
3. I (10633) Remain time: time 111647.000000
4. I (10643) MQTT_DAQ: File written
5. I (150633) MQTT_DAQ: File written

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[ESP_Sprite]

That is curious behavior... I don't think the issue is ESP-IDF here, I tested it on Linux and the behaviour is the same.

EDIT: I think I found it. tm->mon is zero-based, so a month of 0 is January, 1 is February etc. You were calculating the difference between May 30 and Jun 1, and there's indeed a day between those.

[Thanh Quang]

Oh, thanks. I didn't know this, I will test it again soon and post feedback