tmb - valid pointer to the std::tm object where the result will be stored

fmt - pointer to a null-terminated CharT string specifying the conversion format

The format string consists of zero or more conversion specifiers, whitespace characters, and ordinary characters (except %). Each ordinary character is expected to match one character in the input stream in case-insensitive comparison. Each whitespace character matches arbitrary whitespace in the input string. Each conversion specification begins with % character, optionally followed by E or O modifier (ignored if unsupported by the locale), followed by the character that determines the behavior of the specifier. The format specifiers match the POSIX function strptime():

Conversion specifier	Explanation	Writes to fields
%	matches a literal %. The full conversion specification must be %%	(none)
t	matches any whitespace	(none)
n	matches any whitespace	(none)
Year
Y	parses full year as a 4 digit decimal number, leading zeroes permitted but not required	tm_year
EY	parses year in the alternative representation, e.g.平成23年 (year Heisei 23) which writes 2011 to tm_year in ja_JP locale	tm_year
y	parses last 2 digits of year as a decimal number. Range [69,99] results in values 1969 to 1999, range [00,68] results in 2000-2068	tm_year
Oy	parses last 2 digits of year using the alternative numeric system, e.g. 十一 is parsed as 11 in ja_JP locale	tm_year
Ey	parses year as offset from locale's alternative calendar period %EC	tm_year
C	parses the first 2 digits of year as a decimal number (range [00,99])	tm_year
EC	parses the name of the base year (period) in the locale's alternative representation, e.g. 平成 (Heisei era) in ja_JP	tm_year
Month
b	parses the month name, either full or abbreviated, e.g. Oct	tm_mon
h	synonym of b	tm_mon
B	synonym of b	tm_mon
m	parses the month as a decimal number (range [01,12]), leading zeroes permitted but not required	tm_mon
Om	parses the month using the alternative numeric system, e.g. 十二 parses as 12 in ja_JP locale	tm_mon
Week
U	parses the week of the year as a decimal number (Sunday is the first day of the week) (range [00,53]), leading zeroes permitted but not required	tm_year, tm_wday, tm_yday
OU	parses the week of the year, as by %U, using the alternative numeric system, e.g. 五十二 parses as 52 in ja_JP locale	tm_year, tm_wday, tm_yday
W	parses the week of the year as a decimal number (Monday is the first day of the week) (range [00,53]), leading zeroes permitted but not required	tm_year, tm_wday, tm_yday
OW	parses the week of the year, as by %W, using the alternative numeric system, e.g. 五十二 parses as 52 in ja_JP locale	tm_year, tm_wday, tm_yday
Day of the year/month
j	parses day of the year as a decimal number (range [001,366]), leading zeroes permitted but not required	tm_yday
d	parses the day of the month as a decimal number (range [01,31]), leading zeroes permitted but not required	tm_mday
Od	parses the day of the month using the alternative numeric system, e.g. 二十七 parses as 27 in ja_JP locale, leading zeroes permitted but not required	tm_mday
e	synonym of d	tm_mday
Oe	synonym of Od	tm_mday
Day of the week
a	parses the name of the day of the week, either full or abbreviated, e.g. Fri	tm_wday
A	synonym of a	tm_wday
w	parses weekday as a decimal number, where Sunday is 0 (range [0-6])	tm_wday
Ow	parses weekday as a decimal number, where Sunday is 0, using the alternative numeric system, e.g. 二 parses as 2 in ja_JP locale	tm_wday
Hour, minute, second
H	parses the hour as a decimal number, 24 hour clock (range [00-23]), leading zeroes permitted but not required	tm_hour
OH	parses hour from 24-hour clock using the alternative numeric system, e.g. 十八 parses as 18 in ja_JP locale	tm_hour
I	parses hour as a decimal number, 12 hour clock (range [01,12]), leading zeroes permitted but not required	tm_hour
OI	parses hour from 12-hour clock using the alternative numeric system, e.g. 六 reads as 06 in ja_JP locale	tm_hour
M	parses minute as a decimal number (range [00,59]), leading zeroes permitted but not required	tm_min
OM	parses minute using the alternative numeric system, e.g. 二十五 parses as 25 in ja_JP locale	tm_min
S	parses second as a decimal number (range [00,60]), leading zeroes permitted but not required	tm_sec
OS	parses second using the alternative numeric system, e.g. 二十四 parses as 24 in ja_JP locale	tm_sec
Other
c	parses the locale's standard date and time string format, e.g. Sun Oct 17 04:41:13 2010 (locale dependent)	all
Ec	parses the locale's alternative date and time string format, e.g. expecting 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in ja_JP locale	all
x	parses the locale's standard date representation	all
Ex	parses the locale's alternative date representation, e.g. expecting 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in ja_JP locale	all
X	parses the locale's standard time representation	all
EX	parses the locale's alternative time representation	all
D	equivalent to "%m / %d / %y "	tm_mon, tm_mday, tm_year
r	parses locale's standard 12-hour clock time (in POSIX, "%I : %M : %S %p")	tm_hour, tm_min, tm_sec
R	equivalent to "%H : %M"	tm_hour, tm_min
T	equivalent to "%H : %M : %S"	tm_hour, tm_min, tm_sec
p	parses the locale's equivalent of a.m. or p.m.	tm_hour

Note: tm_isdst is not written to, and needs to be set explicitly for use with functions such as mktime