Getting error “String was not recognized as a valid DateTime.”

Question

I am getting error String was not recognized as a valid DateTime while converting string to datetime format. I am trying to convert "25-11-2013 06:25:33 PM" to date format. Do any one can help me to solve this issue.

 protected void text_changed(object sender, EventArgs e)
    {
        if (frm.Text == "")
        {
            Label1.Visible = true;
            Label1.Text = "You can leave from textbox blank";
            return;
        }
        string dt = TextBox1.Text;
        string amt = dt.ToString();
        string ams = amt.ToString() + " " + frm.Text;
        DateTime dts = DateTime.ParseExact(ams, "MM/dd/yyyy hh:mm:ss tt", System.Globalization.CultureInfo.InvariantCulture);
        string ams1 = amt.ToString() + "" + TextBox2.Text;
        DateTime dts1 = DateTime.ParseExact(ams1, "MM/dd/yyyy hh:mm:ss tt", System.Globalization.CultureInfo.InvariantCulture);
        TimeSpan dur = DateTime.Parse(dts1.ToString()).Subtract(DateTime.Parse(dts.ToString()));
        double res = 0.0;
        res = dur.TotalHours * 20;
        TextBox3.Text = res.ToString();

    }

Answer 1

If what the user enters is "25-11-2013 06:25:33 PM" then your format string has to be:

string dateFormat = "dd-MM-yyyy hh:mm:ss tt";

The format string you have in your code "MM/dd/yyyy hh:mm:ss tt" requires the user to enter the date as "11/25/2013 06:25:33 PM". All the custom DateTime format string options are described here: http://msdn.microsoft.com/en-us/library/8kb3ddd4(v=vs.110).aspx

Use a calendar control

You are going to have issues with parsing the dates if you allow users to just enter a free form string. Your best option is to add a calendar control or some other way of structuring the user input so that you don't have to parse a free-form string.

Use the generic converter

Using Convert.ToDateTime will save you a bunch of hassle in setting up the expected formats as it tries it's best to find a date format that will fit. On the other hand you may not get what you expected if the date the user enters can be parsed in multiple ways...

 string dts = "09/10/11 06:25";
 DateTime dt = System.Convert.ToDateTime(dts);

On my Swedish system it gets converted to 2009-10-11, yy/mm/dd but using a US context the expected date is 2011-09-10, mm/dd/yy.

Use CultureInfo if you can

If you can get the user to indicate or select their culture then parsing date/times from free-form will be much easier - since the user is more likely to enter a culturally correct string.

 //this is parsing the datetime using Swedish format
 string theCulture = "sv-SE";
 string localDts = "2013-11-25 06:25";
 DateTime localDt = DateTime.Parse(localDts, System.Globalization.CultureInfo.CreateSpecificCulture(theCulture));

Use an array of format strings

If that isn't possible you should think about the different ways that a user may enter dates and times in your system and add them to an array of supported strings. You may need to add a load of different strings since each format string parses one exact format and the user may enter months,days,hours etc as single digits or omit the seconds part. Here is an example which parses a bunch of different formats, this is in no way complete coverage of all the alternatives...

 //A few different strings to test
 string dts1 = "25-11-2013 6:25:33";
 string dts2 = "11/25/2013 6:25:33";
 string dts3 = "25-11-2013 06:25:33";
 string dts4 = "11/25/2013 06:25:33";
 string dts5 = "25-11-2013 6:25:33 PM";
 string dts6 = "11/25/2013 6:25:33 PM";
 string dts7 = "25-11-2013 06:25:33 PM";
 string dts8 = "11/25/2013 06:25:33 PM";
 string dts9 = "25-11-2013 6:5:33 PM";
 string dts10 = "11/25/2013 6:5:33 PM";

 //The supported datetime formats as an array
 string[] dateFormats = { 
                               "dd-MM-yyyy hh:mm:ss tt",
                               "dd-MM-yyyy h:mm:ss tt",
                               "dd-MM-yyyy h:m:ss tt",
                               "dd-MM-yyyy HH:mm:ss",
                               "dd-MM-yyyy H:mm:ss",
                               "dd-MM-yyyy H:m:ss",
                               "MM/dd/yyyy hh:mm:ss tt",
                               "MM/dd/yyyy h:mm:ss tt",
                               "MM/dd/yyyy h:m:ss tt",
                               "MM/dd/yyyy HH:mm:ss",
                               "MM/dd/yyyy H:mm:ss",
                               "MM/dd/yyyy H:m:ss"
                     };

 //Parse all the sample strings
 DateTime dt1 = DateTime.ParseExact(dts1, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt2 = DateTime.ParseExact(dts2, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt3 = DateTime.ParseExact(dts3, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt4 = DateTime.ParseExact(dts4, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt5 = DateTime.ParseExact(dts5, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt6 = DateTime.ParseExact(dts6, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt7 = DateTime.ParseExact(dts7, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt8 = DateTime.ParseExact(dts8, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt9 = DateTime.ParseExact(dts9, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);
 DateTime dt10 = DateTime.ParseExact(dts10, dateFormats, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None);