ref: ea588fa8a7848ccd7a048251823d72559574f6a8
dir: /doc/man3/ctime.3/
.TH CTIME 3 .SH NAME asctime, ctime, gmtime, localtime, mktime - transform date and time to broken-down time .SH SYNOPSIS #include <time.h> .nf char *asctime(const struct tm *tm); 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 *tm); .fi .SH DESCRIPTION The .BR ctime , .B gmtime and .B localtime functions all take an argument of data type .BR time_t , which represents calendar time. The .B asctime and .B mktime functions both takes an argument representing broken-down time, which is a representation separated into year, month, day and so on. Broken-down time is stored in the struct tm. The call .B ctime(t) is equivalent to .BR asctime(localtime(t)) . It converts the calendar time .I t into a null-terminated string of the form: "Wed Jun 30 21:49:08 1993\\n\\0" In C locale, the abbreviations for the days of the week are "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", and "Sat"; the abbreviations for the months are "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", and "Dec". The .B gmtime function converts the calendar time .I timep into broken-down time representation, expressed as Coordinated Universal Time (UTC). It may return NULL if the specified time cannot be converted to UTC. The .B localtime function converts the calendar time .I timep to broken-down time representation, expressed relative to the user's specified timezone. The .B asctime function converts the broken-down time value .I tm into a null-terminated string with the same format as .B ctime function. The .B mktime function converts a broken-down time structure, expressed as local time, to calendar time representation. The function ignores the values supplied by the caller in the .B tm_wday and .B tm_yday fields and the original values of other fields are not restricted to the ranges indicated above. On successful completion, the values of .B tm_wday and .B tm_yday are set appropriately and the other components are set to represent the specified calendar time within their respective ranges. The final value of .B tm_mday is not set until .B tm_mon and .B tm_year are determined. .SH RETURN VALUE On success, .B gmtime and .B localtime functions return a pointer to a struct tm. On success, .B asctime and .B ctime functions return a pointer to a string. On success, .B mktime function returns the calendar time, expressed as a value of type .BR time_t . On error, .B mktime function returns the value .BR (time_t)-1 . The remaining functions return NULL on error. On error, .B errno is set to indicate the cause of the error. .SH STANDARDS .nf ISO/IEC 9899:1999 7.23.2.3 Paragraph 1,2,3 ISO/IEC 9899:1999 7.23.3.1 Paragraph 1,2,3 ISO/IEC 9899:1999 7.23.3.2 Paragraph 1,2,3 ISO/IEC 9899:1999 7.23.3.3 Paragraph 1,2,3 ISO/IEC 9899:1999 7.23.3.4 Paragraph 1,2,3 .fi .SH SEE ALSO .BR time.h (3)