DTDayOfWeek

Returns an integer indicating the day of the week from a date & time string.

DTDayOfWeek PROTO lpszDateTimeString:DWORD, DateFormat:DWORD

Parameters

lpszDateTimeString - Pointer to a buffer containing the date & time string to check the day of the week for. The format of the date & time string is determined by the DateFormat parameter.
DateFormat - Value indicating the date & time format used in the buffer pointed to by lpszDateTimeString parameter. The parameter can contain one of the following constants as listed in the DateTime Formats page and as defined in the DateTime.inc include file.

Returns

On return EAX will contain a value to indicate the following day:

0 = Monday
1 = Tuesday
2 = Wednesday
3 = Thursday
4 = Friday
5 = Saturday
6 = Sunday

Example

; The following example calculates the first day of the week from a date using the DTDayOfWeek function
.data
szDateTime db DATETIME_STRING dup (0)
.data?
dwDate1 dd ?
dwDayWeek dd ?
dwStartWeek dd ?

.code
Invoke DTDateTimeStringToJulianMillisec, CTEXT("04/06/2009"), DDMMCCYY ; Convert date to julian date
mov dwDate1, eax ; only save date info returned in eax, ignore time info returned in edx

Invoke DTDayOfWeek, CTEXT("04/06/2009"), DDMMCCYY ; Get day of week for date
mov dwDayWeek, eax ; Save the returned integer representing day 0-6

mov ebx, eax
mov eax, dwDate1
sub eax, ebx ; subtract julian date value from day of week integer
mov dwStartWeek, eax ; we have new julian date which is start of the week

Invoke DTJulianToDwordDate, dwStartWeek ; convert new julian date start of week number to a date in dword format
Invoke DTDwordDateTimeToDate, eax, NULL, Addr szDateTime, DDMMCCYY ; convert dword date format to a string value
; szDateTime now contains '01/06/2009'