C Date and time utilities

From cppreference.com

Time manipulation
Defined in header `<ctime>`
difftime	computes the difference between times (function) [edit]
time	returns the current time of the system as time since epoch (function) [edit]
clock	returns raw processor clock time since the program is started (function) [edit]
timespec_get (C++17)	returns the calendar time in seconds and nanoseconds based on a given time base (function) [edit]
timespec_getres (C++26)	returns the resolution of calendar time based on a given time base (function) [edit]
Format conversions
Defined in header `<ctime>`
asctime (deprecated in C++26)	converts a std::tm object to a textual representation (function) [edit]
ctime (deprecated in C++26)	converts a std::time_t object to a textual representation (function) [edit]
strftime	converts a std::tm object to custom textual representation (function) [edit]
Defined in header `<cwchar>`
wcsftime	converts a std::tm object to custom wide string textual representation (function) [edit]
Defined in header `<ctime>`
gmtimegmtime_r (C++26)	converts time since epoch to calendar time expressed as Universal Coordinated Time (function) [edit]
localtimelocaltime_r (C++26)	converts time since epoch to calendar time expressed as local time (function) [edit]
mktime	converts calendar time to time since epoch (function) [edit]
timegm (C++26)	converts calendar time to time since epoch, ignoring the Daylight Saving Time flag (function) [edit]