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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>
struct tm;

Structure holding a calendar date and time broken down into its components.

Member objects

int tm_sec	seconds after the minute – [​0​, 61](until C99)[​0​, 60](since C99) (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)

Notes

The Standard mandates only the presence of the aforementioned members in either order. The implementations usually add more data-members to this structure.

Example

Run this code

#include <stdio.h>
#include <time.h>
 
int main(void)
{
    struct tm start = {.tm_year = 2022 - 1900, .tm_mday = 1};
    mktime(&start);
    printf("%s", asctime(&start)); // note implicit trailing '\n'
}

Output:

Sat Jan  1 00:00:00 2022

References

• C23 standard (ISO/IEC 9899:2024):

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

• 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

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 tm