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)
gmtime	converts time since epoch to calendar time expressed as Universal Coordinated Time (function)
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)
declval (C++11)