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# Standard library header <ctime>

From cppreference.com
< cpp‎ | header

This header was originally in the C standard library as `<time.h>`.

This header is part of the C-style date and time library.

### [edit] Macro Constants

CLOCKS_PER_SEC | number of processor clock ticks per second (macro constant) [edit]
NULL | implementation-defined null pointer constant (macro constant) [edit]

### [edit] Types

clock_t | process running time (typedef) [edit]
size_t | unsigned integer type returned by the `sizeof` operator (typedef) [edit]
time_t | time since epoch type (typedef) [edit]
tm | calendar time type (class) [edit]

### [edit] Functions

##### Time manipulation
clock | returns raw processor clock time since the program is started (function) [edit]
time | returns the current time of the system as time since epoch (function) [edit]
difftime | computes the difference between times (function) [edit]
##### Format conversions
ctime | converts a `time_t` object to a textual representation (function) [edit]
asctime | converts a `tm` object to a textual representation (function) [edit]
strftime | converts a `tm` object to custom textual representation (function) [edit]
wcsftime | converts a tm object to custom wide string textual representation (function) [edit]
gmtime | converts time since epoch to calendar time expressed as Universal Coordinated Time (function) [edit]
localtime | converts time since epoch to calendar time expressed as local time (function) [edit]
mktime | converts calendar time to time since epoch (function) [edit]

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