C Library - <time.h>

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The time.h header defines four variable types, two macro and various functions for manipulating date and time.

Library Variables

Following are the variable types defined in the header time.h −

Sr.No. Variable & Description
1

size_t

This is the unsigned integral type and is the result of the sizeof keyword.
2

clock_t

This is a type suitable for storing the processor time.
3

time_t is

This is a type suitable for storing the calendar time.
4

struct tm

This is a structure used to hold the time and date.

The tm structure has the following definition −

struct tm {
   int tm_sec;         /* seconds,  range 0 to 59          */
   int tm_min;         /* minutes, range 0 to 59           */
   int tm_hour;        /* hours, range 0 to 23             */
   int tm_mday;        /* day of the month, range 1 to 31  */
   int tm_mon;         /* month, range 0 to 11             */
   int tm_year;        /* The number of years since 1900   */
   int tm_wday;        /* day of the week, range 0 to 6    */
   int tm_yday;        /* day in the year, range 0 to 365  */
   int tm_isdst;       /* daylight saving time             */
};

Library Macros

Following are the macros defined in the header time.h −

Sr.No. Macro & Description
1

NULL

This macro is the value of a null pointer constant.
2

CLOCKS_PER_SEC

This macro represents the number of processor clocks per second.

Library Functions

Following are the functions defined in the header time.h −

Sr.No. Function & Description
1 char *asctime(const struct tm *timeptr)

Returns a pointer to a string which represents the day and time of the structure timeptr.
2 clock_t clock(void)

Returns the processor clock time used since the beginning of an implementation defined era (normally the beginning of the program).
3 char *ctime(const time_t *timer)

Returns a string representing the localtime based on the argument timer.
4 double difftime(time_t time1, time_t time2)

Returns the difference of seconds between time1 and time2 (time1-time2).
5 struct tm *gmtime(const time_t *timer)

The value of timer is broken up into the structure tm and expressed in Coordinated Universal Time (UTC) also known as Greenwich Mean Time (GMT).
6 struct tm *localtime(const time_t *timer)

The value of timer is broken up into the structure tm and expressed in the local time zone.
7 time_t mktime(struct tm *timeptr)

Converts the structure pointed to by timeptr into a time_t value according to the local time zone.
8 size_t strftime(char *str, size_t maxsize, const char *format, const struct tm *timeptr)

Formats the time represented in the structure timeptr according to the formatting rules defined in format and stored into str.
9 time_t time(time_t *timer)

Calculates the current calender time and encodes it into time_t format.
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