DTDayOfWeek

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

DTDayOfWeek PROTO lpszDateTimeString:QWORD, DateFormat:QWORD

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 RAX 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?
qwDate1 dq ?
qwDayWeek dq ?
qwStartWeek dq ?

.code
Invoke DTDateTimeStringToJulianMillisec, CTEXT("04/06/2009"), DDMMCCYY ; Convert date to julian date
mov qwDate1, rax ; 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 qwDayWeek, rax ; Save the returned integer representing day 0-6

mov rbx, rax
mov rax, qwDate1
sub rax, rbx ; subtract julian date value from day of week integer
mov qwStartWeek, rax ; we have new julian date which is start of the week

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