# Date and time utilities

From cppreference.com
< c

### Functions

##### Time manipulation
Defined in header `<time.h>`
difftime | computes the difference between times (function)
time | returns the current calendar time of the system as time since epoch (function)
clock | returns raw processor clock time since the program is started (function)
timespec_get (C11) | returns the calendar time in seconds and nanoseconds based on a given time base (function)
timespec_getres (C23) | returns the resolution of calendar time based on a given time base (function)
##### Format conversions
Defined in header `<time.h>`
asctime asctime_s (deprecated in C23)(C11) | converts a tm object to a textual representation (function)
ctime ctime_s (deprecated in C23)(C11) | converts a time_t object to a textual representation (function)
strftime | converts a tm object to custom textual representation (function)
Defined in header `<wchar.h>`
wcsftime (C95) | converts a tm object to custom wide string textual representation (function)
Defined in header `<time.h>`
gmtime gmtime_r gmtime_s (C23)(C11) | converts time since epoch to calendar time expressed as Coordinated Universal Time (UTC) (function)
localtime localtime_r localtime_s (C23)(C11) | converts time since epoch to calendar time expressed as local time (function)
mktime | converts calendar time to time since epoch (function)

### Constants

Defined in header `<time.h>`
CLOCKS_PER_SEC | number of processor clock ticks per second (macro constant)

### Types

Defined in header `<time.h>`
tm | calendar time type (struct)
time_t | calendar time since epoch type (typedef)
clock_t | processor time since era type (typedef)
timespec (C11) | time in seconds and nanoseconds (struct)

### References

- C17 standard (ISO/IEC 9899:2018):

  - 7.27 Date and time <time.h> (p: 284-291)

  - 7.29.5.1 The wcsftime function (p: 320-321)

  - 7.31.14 Date and time <time.h> (p: 333)

- C11 standard (ISO/IEC 9899:2011):

  - 7.27 Date and time <time.h> (p: 388-397)

  - 7.29.5.1 The wcsftime function (p: 439-440)

  - 7.31.14 Date and time <time.h> (p: 456)

- C99 standard (ISO/IEC 9899:1999):

  - 7.23 Date and time <time.h> (p: 338-347)

  - 7.24.5.1 The wcsftime function (p: 385-386)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.12 DATE AND TIME <time.h>

### See also

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