Renormalizes local calendar time expressed as astruct tm object and also converts it to time since epoch as atime_t object.arg->tm_wday andarg->tm_yday are ignored. The values inarg are not checked for being out of range.

A negative value ofarg->tm_isdst causesmktime to attempt to determine if Daylight Saving Time was in effect in the specified time.

If the conversion totime_t is successful, thearg object is modified. All fields ofarg are updated to fit their proper ranges.arg->tm_wday andarg->tm_yday are recalculated using information available in other fields.

[edit]Parameters

[edit]Return value

The time since epoch as atime_t object on success, or-1 ifarg cannot be represented as atime_t object (POSIX also requiresEOVERFLOW to be stored inerrno in this case).

[edit]Notes

If thestructtm object was obtained from POSIXstrptime or equivalent function, the value oftm_isdst is indeterminate, and needs to be set explicitly before callingmktime.

[edit]Example

#define _POSIX_C_SOURCE 200112L // for setenv on gcc#include <stdio.h>#include <stdlib.h>#include <time.h> int main(void){    setenv("TZ","/usr/share/zoneinfo/America/New_York",1);// POSIX-specific structtmtm=*localtime(&(time_t){time(NULL)});printf("Today is           %s",asctime(&tm));printf("(DST is %s)\n",tm.tm_isdst?"in effect":"not in effect");tm.tm_mon-=100;// tm_mon is now outside its normal range    mktime(&tm);// tm_isdst is not set to -1; today's DST status is usedprintf("100 months ago was %s",asctime(&tm));printf("(DST was %s)\n",tm.tm_isdst?"in effect":"not in effect");}

Today is           Fri Apr 22 11:53:36 2016(DST is in effect)100 months ago was Sat Dec 22 10:53:36 2007(DST was not in effect)

[edit]References

[edit]See also

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