mktime

mktime

Determines the time represented by a struct tm value

 #include <time.h> time_t mktime ( struct tm *timeptr  );

The mktime( ) function calculates the local calendar time represented by the member values in the object referenced by the pointer argument.

The type struct tm is defined in time.h as follows:

 struct tm {   int tm_sec;         /* Seconds (0-60; 1 leap second) */   int tm_min;         /* Minutes (0-59) */   int tm_hour;        /* Hours   (0-23) */   int tm_mday;        /* Day     (1-31) */   int tm_mon;         /* Month   (0-11) */   int tm_year;        /* Year    (difference from 1900) */   int tm_wday;        /* Day of week (0-6)   */   int tm_yday;        /* Day of year (0-365) */   int tm_isdst;       /* Daylight saving time (-1, 0, 1) */ };

The member tm_isdst is equal to 0 if daylight saving time is not in effect, or 1 if it is. A negative value indicates that the information is not available, in which case mktime( ) attempts to calculate whether daylight saving time is applicable at the time represented by the other members.

The mktime( ) function ignores the tm_wday and tm_yday members in determining the time, but does use tm_isdst. The other members may contain values outside their normal ranges. Once it has calculated the time represented, mktime( ) adjusts the struct tm members so that each one is within its normal range, and also sets tm_wday and tm_yday accordingly. The return value is the number of seconds from the epoch (usually midnight on January 1, 1970, UTC) to the time represented in the structure, or -1 to indicate an error.

Example

   time_t seconds;   struct tm sometime;   sometime.tm_sec   = 10;   sometime.tm_min   = 80;   sometime.tm_hour  = 40;   sometime.tm_mday  = 23;   sometime.tm_mon   = 1;   sometime.tm_year  = 105;   sometime.tm_wday  = 11;   sometime.tm_yday  = 111;   sometime.tm_isdst = -1;   seconds = mktime( &sometime );   if ( seconds == -1 )   {     printf( "mktime( ) couldn't make sense of its input.\n" );     return -1;   }   printf( "The return value, %ld, represents %s",           (long)seconds, ctime(&seconds) );   printf( "The structure has been adjusted as follows:\n"           "tm_sec   == %d\n"           "tm_min   == %d\n"           "tm_hour  == %d\n"           "tm_mday  == %d\n"           "tm_mon   == %d\n"           "tm_year  == %d\n"           "tm_wday  == %d\n"           "tm_yday  == %d\n"           "tm_isdst == %d\n",           sometime.tm_sec,           sometime.tm_min,           sometime.tm_hour,           sometime.tm_mday,           sometime.tm_mon,           sometime.tm_year,           sometime.tm_wday,           sometime.tm_yday,           sometime.tm_isdst );   printf( "The structure now represents %s", asctime( &sometime )); }

This program produces the following output:

 The return value, 1109262010, represents Thu Feb 24 17:20:10 2005 The structure has been adjusted as follows: tm_sec   == 10 tm_min   == 20 tm_hour  == 17 tm_mday  == 24 tm_mon   == 1 tm_year  == 105 tm_wday  == 4 tm_yday  == 54 tm_isdst == 0 The structure now represents Thu Feb 24 17:20:10 2005

Example

See Also