如果SYSTEMTIME无法做到这一点，根据 msdn ，当将 SYSTEMTIME 转换为 FILETIME 时，将忽略wDayOfWeek 成员。

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

 WORD dayofweek = t.wDayOfWeek; 
 

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)?

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;