формат даты и времени (format date and time)
Возвращаемое значение (Return value)
Provided that the result string, including the terminating null
byte, does not exceed max bytes, strftime() returns the number of
bytes (excluding the terminating null byte) placed in the array
s. If the length of the result string (including the terminating
null byte) would exceed max bytes, then strftime() returns 0, and
the contents of the array are undefined.
Note that the return value 0 does not necessarily indicate an
error. For example, in many locales %p yields an empty string.
An empty format string will likewise yield an empty string.
