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.

C time.h library function

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


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.