Returns the serial number of the date represented by date_text
[C++]
static int DateValue(
   double& ddt,
   const char* date_text
);
static int DateValue(
   long& ldt,
   const char* date_text
);
A reference to a value that will contain a serial date if the function succeeds.
A string containing a date.
A reference to a value that will contain a serial date if the function succeeds.
Zero if the function has been called successfully; non-zero
            if the function could not be called.
            See Error codes for a list
            of return values.
See the Microsoft Excel on-line Help for full details about
            this function.
Header: xlfuncs.h