Calculate the number of weekdays between two dates in C#

Question

How can I get the number of weekdays between two given dates without just iterating through the dates between and counting the weekdays?

Seems fairly straightforward

Answer 1

This should do better than the solution by dcp:

    /// 

    /// Count Weekdays between two dates
    /// 
    /// first date
    /// second date
    /// weekdays between the two dates, including the start and end day
    internal static int getWeekdaysBetween(DateTime dtmStart, DateTime dtmEnd)
    {
        if (dtmStart > dtmEnd)
        {
            DateTime temp = dtmStart;
            dtmStart = dtmEnd;
            dtmEnd = temp;
        }

        /* Move border dates to the monday of the first full week and sunday of the last week */
        DateTime startMonday = dtmStart;
        int startDays = 1;
        while (startMonday.DayOfWeek != DayOfWeek.Monday)
        {
            if (startMonday.DayOfWeek != DayOfWeek.Saturday && startMonday.DayOfWeek != DayOfWeek.Sunday)
            {
                startDays++;
            }
            startMonday = startMonday.AddDays(1);
        }

        DateTime endSunday = dtmEnd;
        int endDays = 0;
        while (endSunday.DayOfWeek != DayOfWeek.Sunday)
        {
            if (endSunday.DayOfWeek != DayOfWeek.Saturday && endSunday.DayOfWeek != DayOfWeek.Sunday)
            {
                endDays++;
            }
            endSunday = endSunday.AddDays(1);
        }

        int weekDays;

        /* calculate weeks between full week border dates and fix the offset created by moving the border dates */
        weekDays = (Math.Max(0, (int)Math.Ceiling((endSunday - startMonday).TotalDays + 1)) / 7 * 5) + startDays - endDays;

        return weekDays;
    }