UnixTime to readable date

Question

What is the best way to convert UnixTime to a date?

Is there a function for it or an algorithm?

Answer 1

Unix time is seconds since epoch (1970-01-01). Depending on what you mean, you can convert it to a struct tm with localtime or convert it to a string with strftime.

time_t t = time(NULL);
struct tm *tm = localtime(&t);
char date[20];
strftime(date, sizeof(date), "%Y-%m-%d", tm);

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As the manual to localtime states

The return value points to a statically allocated struct which might be overwritten by subsequent calls to any of the date and time functions.

This is what some refer to as data races. This happens when two or more threads call localtime simultaneously.

To protect from this, some suggest using localtime_s, which is a Microsoft only function. On POSIX systems, you should use localtime_r instead

The localtime_r() function does the same, but stores the data in a user-supplied struct.

Usage would look like

time_t t = time(NULL);
struct tm res;
localtime_r(&t, &res);

Answer 2

I'm going to assume you have the time in a time_t. First you need to convert that to a struct tm. You can do this with localtime or gmtime, depending on whether you want to use the local timezone or GMT.

Then you can format that struct tm as a string with strftime. For example, to get a date like 2012-11-24 you'd use the format "%Y-%m-%d".

Answer 3

See also Convert Unix/Linux time to Windows FILETIME

This function should convert from UnixTime into Windows SYSTEMTIME

SYSTEMTIME intChromeTimeToSysTime(long long int UnixTime)
{
    ULARGE_INTEGER uLarge;
    uLarge.QuadPart = UnixTime;
    FILETIME ftTime;
    ftTime.dwHighDateTime = uLarge.HighPart;
    ftTime.dwLowDateTime = uLarge.LowPart;
    SYSTEMTIME stTime;
    FileTimeToSystemTime(&ftTime, &stTime);
    return stTime;

}