time_t

 

C

Compiler support

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Strings library

Algorithms

Numerics

Date and time utilities

Input/output support

Localization support

Concurrency support (C11)

Technical Specifications

Symbol index

 

Date and time utilities

Functions

Time manipulation

difftime

time

clock

timespec_get (C11)

timespec_getres (C23)

Format conversions

asctimeasctime_s (deprecated in C23)(C11)

ctimectime_s (deprecated in C23)(C11)

strftime

wcsftime (C95)

gmtimegmtime_rgmtime_s (C23)(C11)

localtimelocaltime_rlocaltime_s (C23)(C11)

mktime

Constants

CLOCKS_PER_SEC

Types

tm

time_t

clock_t

timespec (C11)

 

Defined in header <time.h>
typedef /* unspecified */ time_t;

Real arithmetic type capable of representing times.

Although not defined by the C standard, this is almost always an integral value holding the number of seconds (not counting leap seconds) since 00:00, Jan 1 1970 UTC, corresponding to POSIX time.

Notes

The standard uses the term calendar time when referring to a value of type time_t.

Example

Show the start of the epoch.

Run this code

#include <stdio.h>
#include <time.h>
#include <stdint.h>
 
int main(void)
{
    time_t epoch = 0;
    printf("%jd seconds since the epoch began\n", (intmax_t)epoch);
    printf("%s", asctime(gmtime(&epoch)));
}

Possible output:

0 seconds since the epoch began
Thu Jan  1 00:00:00 1970

References

• C17 standard (ISO/IEC 9899:2018):

• 7.27.1/3 Components of time (p: 284)

• C11 standard (ISO/IEC 9899:2011):

• 7.27.1/3 Components of time (p: 388)

• C99 standard (ISO/IEC 9899:1999):

• 7.23.1/3 Components of time (p: 338)

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

• 4.12.1 Components of time

See also

time	returns the current calendar time of the system as time since epoch (function)
localtimelocaltime_rlocaltime_s (C23)(C11)	converts time since epoch to calendar time expressed as local time (function)
gmtimegmtime_rgmtime_s (C23)(C11)	converts time since epoch to calendar time expressed as Coordinated Universal Time (UTC) (function)
C++ documentation for time_t