How to set datetime with HH:mm:ss = 00:00:00 instead of 12:00:00?

DateTime a1 = new DateTime(Convert.ToDateTime(txtStartDate.Text).Year, Convert.ToDateTime(txtStartDate.Text).Month, Convert.ToDateTime(txtStartDate.Text).Da开发者_运维技巧y, 0, 0, 0);

I have tried to change system time from 12 hrs hh to 24 hours HH and restart web site insert still is 12:00:00

I want 00:00:00

What you're seeing is a formatting issue rather than a data issue. It really is 00:00:00, but however you're converting it to a string is showing it as 12:00:00, presumably with an implicit "am". Don't forget that a DateTime doesn't actually have a format in it - it's just the date/time. You can format it appropriately yourself, e.g.

Console.WriteLine(a1.ToString("yyyy-MM-dd HH:mm:ss"));

All this aside, I would strongly recommend that you don't create the DateTime this way. Personally I prefer to use DateTime.TryParseExact or DateTime.ParseExact anyway, rather than using "whatever patterns the current culture happens to prefer", but even if you do want to parse with Convert.ToDateTime, it would be clearer to do it once, and then use the Date property to get a DateTime with the time set to 0:

DateTime a1 = Convert.ToDateTime(txtStartDate.Text).Date;

Well, technically there is no time as 00:00:00. After 11:59:59 it becomes 12:00:00. Maybe I'm just not understanding what you're trying to do :)

You could have special logic in your code that modifies it such that if it is 12:00:00, then display it as 00:00:00 or something. But out of the box there is no magic or format string that will do this.

You could simplify that a bit by specifying a format:

DateTime a1 = DateTime.Parse(string.Format("{0} 00:00:00", "01/27/2011"),
                                         CultureInfo.GetCultureInfo("en-US"));

I don't know what format your textbox is, but assuming it is 01/27/2011 (US format) you can change the above snippet to work easily:

DateTime a1 = DateTime.Parse(string.Format("{0} 00:00:00", txtStartDate.Text),
                                         CultureInfo.GetCultureInfo("en-US"));

Change your CultureInfo.GetCultureInfo (it implements IFormatProvider) to the one you're using. Ideally you should parse the date into a UTC date but that's a different discussion.

When you want to add a DateTime Object to a string or want to display it in some form of text, the ToString()-Method is used automatically. The ToString() uses "en-US" as default culture. Ofcourse you can manually call ToString() and parametrise it with any CultureInfo you wish but sometimes that is not possible.

When you access DateTime-objects via Databinding for example, you can't pass any CultureInfo and end up with a date string localised in "en-US". In this case you need to set the CultureInfo for the current thread like:

Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture("de-DE");

After this line is called all dates will be localised in "de-DE" as long as you don't manually call ToString() with a different CultureInfo.

Have a read on this link: https://msdn.microsoft.com/en-us/library/k494fzbf(v=vs.110).aspx

You could simplify that

if (!string.IsNullOrEmpty(txtStartDate.Text))
            {
                string startDate = Convert.ToDateTime(txtStartDate.Text).ToString("yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture);
            }