Time isn't converted correct from Unix time

Projects Programming
1

I'm trying to convert unix time to readable format but if i do the conversion it's off by 30 years and 1 day and I dont have a clue why (time is correct). Hope someone can help me out.

Code :

char   buf[80];
time_t rawtime = epoch; // time(epoch);
struct tm ts = *localtime(&rawtime);
strftime(buf, sizeof(buf), "%a %Y-%m-%d %H:%M:%S %Z", &ts);
Serial.println(buf);

Output :

Seconds since Jan 1 1900 = 3878967015
Unix time = 1669978215
Sun 2052-12-01 10:50:15 ?

2

unix time starts 1970, but some system use seconds since 2000

3

"In 1984, the International Astronomical Union decided that epoch 2000.0 would begin at 1200 UTC on January 1, 2000."

What Is Epoch? (techtarget.com)

4

@noiasca in astronomy

5

Thx, that was indeed the problem.Substracted the difference and now it works.

char   buf[80];
time_t rawtime = epoch-946684800; // time(epoch);
struct tm ts = *localtime(&rawtime);
strftime(buf, sizeof(buf), "%a %Y-%m-%d %H:%M:%S %Z", &ts);
Serial.println(buf);

Output :

Seconds since Jan 1 1900 = 3878974629
Unix time = 1669985829
Fri 2022-12-02 12:57:09 ?

6

I tried to "autodetect" the epoche and calculate a difference/offset on wokwi:

epoch_test.ino - Wokwi Arduino and ESP32 Simulator

7

Rather than using a magic number, you can use UNIX_OFFSET, provided by Arduino's time.h.

8

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