mktime returns wrong timestamp (off by a whole month)

c, date, mktime, time, utc

Solution

C11 7.27.1 Components of time

int tm_sec; // seconds after the minute — [0, 60]
int tm_min; // minutes after the hour — [0, 59]
int tm_hour; // hours since midnight — [0, 23]
int tm_mday; // day of the month — [1, 31]
int tm_mon; // months since January — [0, 11]
int tm_year; // years since 1900
int tm_wday; // days since Sunday — [0, 6]
int tm_yday; // days since January 1 — [0, 365]
int tm_isdst; // Daylight Saving Time flag

`tm_mon` starts with `0`, not `1`. So the value of `5` means it's June, not May.

Problem

I use `mktime` to create a unix timestamp from my current local time: ``` #include <time.h> int _tmain(int argc, _TCHAR* argv[]) { struct tm info; // 16.05.2014 info.tm_mday = 16; info.tm_mon = 5; info.tm_year = 114; // Years since 1900 // 08:00:00 Uhr info.tm_hour = 8; info.tm_min = 0; info.tm_sec = 0; // Convert to Unix timestamp info.tm_isdst = -1; time_t timestamp = mktime(&info); printf("Timestamp: %i", timestamp); } ``` This gives me: 1402898400 When converting this back to a human readable time (via some website) this translates to: 16.06.2014 08:00:00 As you can see this is one month off from what I expected (put in May (5), got out June (6)). Why?

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