如何从C＃中的日期字符串获取本月的最后一天？

Question

How would I find the last day of current month stated in the String?

Eg if the string was "January 2018" how would I record 31/01/2018 as the date

Currently it defaults to the first of the month:

string nextEventDateString = "January 2018"
DateTime tempDate;

if (DateTime.TryParse(nextEventDateString, out tempDate))
{
    cRecord.ComplianceDate = tempDate.ToString("dd/MM/yyyy");
    cRecord.NotifyDate = tempDate.AddMonths(-1).ToString("dd/MM/yyyy");
    cRecord.WarningDate = tempDate.AddMonths(1).ToString("dd/MM/yyyy");
}

Answer 1

First parse the string to DateTime , later add one month and subtract one day from the date, it will give you the last day for the month like:

string dateString = "January 2018";
DateTime dt = DateTime.ParseExact(dateString, "MMMM yyyy", CultureInfo.InvariantCulture);

DateTime lastDateForMonth = dt.AddMonths(1).AddDays(-1);

As a side note, It appears you are keeping a string representation of DateTime in your object properties. It would be better to keep DateTime instead of string . Use string representation in formatting/presentation. IMO. Also continue using DateTime.TryParse or DateTime.TryParseExact with a format, as it will save you from the exception in case of failed parsing.

Answer 2

Using this:

var days = DateTime.DaysInMonth(2018, 01);

You will get the number of days for the January of 2018. Then you could build your datetime like below:

DateTime lastDayForMonth = new DateTime(year, month, days-1);

where in place of year and month you will place the year and the month you are interested in.

In any case, you have to parse your string first and create a valid DateTime , in order you get the year, dt.Year and the month dt.Month ( dt is the parsed date time string).

Answer 3

Try this:

DateTime today = DateTime.Today;
DateTime endOfMonth = new DateTime(today.Year, today.Month, 1).AddMonths(1).AddDays(-1);