C time.h Library Function

C time.h library functions: The C time.h library function defines four variable types, two macro and various functions for manipulating date and time.

Library Variables

Variables	Description
size_t	It is the unsigned integral type and is the result of the size of the keyword
clock_t( )	This is a type suitable for storing the processor time
time_t	This is a type suitable for storing the calendar time.
struct tm	This is a structure used to hold the time and date

Example

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

Macro	Description
NULL	macro is the value of a null pointer constant
CLOCLKS_PER_SEC	Macro represents the number of processor clocks per second

Library Functions

Function	Description
char asctime(const struct tm timeptr)	Returns a pointer to a string which represents the day and time of the structure timeptr
clock_t clock(void)	Returns the processor clock time used since the beginning of an implementation-defined era
char ctime(const time_t timer	Returns a string representing the localtime based on the argument timer
double difftime(time_t time1, time_t time2)	Returns the difference of seconds between time1 and time2 (time1-time2)
struct tm gmtime(const time_t timer)	The value of the timer is broken up into the structure tm and expressed in Coordinated Universal Time (UTC) also known as Greenwich Mean Time (GMT)
struct tm local time(const time_t timer)	The value of the timer is broken up into the structure tm and expressed in the local time zone
time_t mktime(struct tm *timeptr)	It converts the structure pointed to by timeptr into a time_t value according to the local time zone
size_t strftime(char str, size_t max size, 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
time_t time(time_t *timer)	It calculates the current calendar time and encodes it into time_t format.