std::tm

Structure holding a calendar date and time broken down into its components.

int tm_sec	seconds after the minute – [0, 61](until C++11) / [0, 60] (since C++11)^{[note 1]} (public member object)
int tm_min	minutes after the hour – [0, 59] (public member object)
int tm_hour	hours since midnight – [0, 23] (public member object)
int tm_mday	day of the month – [1, 31] (public member object)
int tm_mon	months since January – [0, 11] (public member object)
int tm_year	years since 1900 (public member object)
int tm_wday	days since Sunday – [0, 6] (public member object)
int tm_yday	days since January 1 – [0, 365] (public member object)
int tm_isdst	Daylight Saving Time flag. The value is positive if DST is in effect, zero if not and negative if no information is available (public member object)

↑ Range allows for a positive leap second. Two leap seconds in the same minute are not allowed (the range 0..61 was a defect introduced in C89 and corrected in C99)

localtime	converts time since epoch to calendar time expressed as local time (function) [edit]
gmtime	converts time since epoch to calendar time expressed as Universal Coordinated Time (function) [edit]
C documentation for tm

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Technical Specifications

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
Relational operators
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Pairs and tuples
pair
tuple (C++11)
piecewise_construct_t (C++11)
piecewise_construct (C++11)
integer_sequence (C++14)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Type operations
declval (C++11)
as_const (C++17)