CTIME(3) Linux Programmer's Manual CTIME(3) NAME asctime, ctime, gmtime, localtime, mktime - transform binary date and time to ASCII SYNOPSIS #include char *asctime(const struct tm *timeptr); char *ctime(const time_t *timep); struct tm *gmtime(const time_t *timep); struct tm *localtime(const time_t *timep); time_t mktime(struct tm *timeptr); extern char *tzname[2]; long int timezone; extern int daylight; DESCRIPTION The ctime(), gmtime() and localtime() functions all take an argument of data type time_t which represents calendar time. When interpreted as an absolute time value, it rep- resents the number of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal Time (UTC). The asctime() and mktime() functions both take an argument representing broken-down time which is a binary represen- tation separated into year, month, day, etc. Broken-down time is stored in the structure tm which is defined in as follows: struct tm { int tm_sec; /* seconds */ int tm_min; /* minutes */ int tm_hour; /* hours */ int tm_mday; /* day of the month */ int tm_mon; /* month */ int tm_year; /* year */ int tm_wday; /* day of the week */ int tm_yday; /* day in the year */ int tm_isdst; /* daylight saving time */ }; The members of the tm structure are: tm_sec The number of seconds after the minute, normally in the range 0 to 59, but can be up to 61 to allow for leap seconds. tm_min The number of minutes after the hour, in the range 0 to 59. tm_hour The number of hours past midnight, in the range 0 to 23. tm_mday The day of the month, in the range 1 to 31. tm_mon The number of months since January, in the range 0 to 11. tm_year The number of years since 1900. tm_wday The number of days since Sunday, in the range 0 to 6. tm_yday The number of days since January 1, in the range 0 to 365. tm_isdst A flag that indicates whether daylight saving time is in effect at the time described. The value is positive if daylight saving time is in effect, zero if it is not, and negative if the information is not available. The ctime() function converts the calendar time timep into a string of the form "Wed Jun 30 21:49:08 1993\n" The abbreviations for the days of the week are `Sun', `Mon', `Tue', `Wed', `Thu', `Fri', and `Sat'. The abbre- viations for the months are `Jan', `Feb', `Mar', `Apr', `May', `Jun', `Jul', `Aug', `Sep', `Oct', `Nov', and `Dec'. The return value points to a statically allocated string which might be overwritten by subsequent calls to any of the date and time functions. The function also sets the external variable tzname with information about the current time zone. The gmtime() function converts the calendar time timep to broken-down time representation, expressed in Coordinated Universal Time (UTC). The localtime() function converts the calendar time timep to broken-time representation, expressed relative to the user's specified time zone. The function sets the external variables tzname with information about the cur- rent time zone, timezone with the difference between Coor- dinated Universal Time (UTC) and local standard time in seconds, and daylight to a non-zero value if standard US daylight savings time rules apply. The asctime() function converts the broken-down time value timeptr into a string with the same format as ctime(). The return value points to a statically allocated string which might be overwritten by subsequent calls to any of the date and time functions. The mktime() function converts a broken-down time struc- ture, expressed as local time, to calendar time represen- tation. The function ignores the specified contents of the structure members tm_wday and tm_yday and recomputes them from the other information in the broken-down time structure. If structure members are outside their legal interval, they will be normalized (so that, e.g., 40 Octo- ber is changed into 9 November). Calling mktime() also sets the external variable tzname with information about the current time zone. If the specified broken-down time cannot be represented as calendar time (seconds since the epoch), mktime() returns a value of (time_t)(-1) and does not alter the tm_wday and tm_yday members of the broken- down time structure. CONFORMING TO SVID 3, POSIX, BSD 4.3, ISO 9899 SEE ALSO date(1), gettimeofday(2), time(2), tzset(3), difftime(3), strftime(3), newctime(3) BSD April 26, 1996 CTIME(3)