Given Date, Get Day of Week - SYSTEMTIME

Question

Is it possible to determine the day of the week, using SYSTEMTIME, if a date (month-day-year) is provided or is this structure one-way only?

What is the most lightweight way to accomplish what I am asking if SYSTEMTIME cannot do it (using Win32)?

Answer 1

According to the msdn, the wDayOfWeek member is ignored when converting SYSTEMTIME to FILETIME. When converting back, it's filled in.

SYSTEMTIME t = { 2010, 6, -1 /*ignored*/, 11 };
FILETIME ft;
HRESULT hrto   = SystemTimeToFileTime( &t, &ft );
HRESULT hrback = FileTimeToSystemTime( &ft, &t );

WORD dayofweek = t.wDayOfWeek;

Answer 2

Use SystemTimeToFileTime to covert the SYSTEMTIME to a FILETIME. Then use FileTimeToSystemTimeto convert it to a SYSTEMTIME with day of week.

Answer 3

Another way of doing it that might be a bit more platform independent would be to use localtime or gmtime.

For example, print current day of week:

struct tm *timeval;
time_t tt;
tt = time( NULL );
timeval = localtime( &tt );
// print zero based day of week
printf( "day of week = %d\n", timeval->tm_wday );